Full report

Original page 1

NASA/TM-2000-206892, Vol. 11 SeaWiFS Postlaunch Technical Report Series Stanford B. Hooker and Elaine R. Firestone, Editors Volume 11, SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3 John E. 0 'Reilly, St_phane Maritorena, Margaret C. O'Brien, David A. Siegel, Dierdre Toole, David Menzies, Raymond C. Smith, James L. Mueller, B. Greg Mitchell, Mati Kahru, Francisco P. Chavez, P. Strutton, Glenn E Cota, Stanford B. Hooker, Charles R. McClain, Kendall L. Carder, Frank M_ller-Karger, Larry Harding, Andrea Magnuson, David Phinney, Gerald E Moore, James Aiken, Kevin R. Arrigo, Ricardo Letelier, and Mao' Culver National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 October 2000

Original page 2

The NASA STI Program Office ... in Profile Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role. The NASA STI Program Office is operated by Langley Research Center, the lead center for NASA's scientific and technical information. The NASA STI Program Office provides access to the NASA STI Database, the largest collection of aeronautical and space science STI in the world. The Program Office is also NASA's institutional mechanism for disseminating the results of its research and development activities. These results are published by NASA in the NASA STI Report Series, which includes the following report types: • TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA's counterpart of peer-reviewed formal professional papers but has less stringent limitations on manuscript length and extent of graphic presentations. • TECHNICAL MEMORANDUM. Scientific and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis. • CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored contractors and grantees. • CONFERENCE PUBLICATION. Collected papers from scientific and technical conferences, symposia, seminars, or other meetings sponsored or cosponsored by NASA. • SPECIAL PUBLICATION. Scientific, technical, or historical information from NASA programs, projects, and mission, often concerned with subjects having substantial public interest. TECHNICAL TRANSLATION. English-language translations of foreign scientific and technical material pertinent to NASA's mission. Specialized services that complement the STI Program Office's diverse offerings include creating custom thesauri, building customized databases, organizing and publishing research results... even providing videos. For more information about the NASA STI Program Office, see the following: ° Access the NASA STI Program Home Page at http://www.sti.nasa.gov/STI-homepage.html • E-mail your question via the Internet to help@sti.nasa.gov • Fax your question to the NASA Access Help Desk at (301) 621-0134 • Telephone the NASA Access Help Desk at (301) 621-0390 Write to: NASA Access Help Desk NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076-1320

Original page 3

NASA/TM-2000-206892, Vol. 11 SeaWiFS Postlaunch Technical Report Series Stanford B. Hooker, Editor NASA Goddard Space Flight Center, Greenbelt, Maryland Elaine R. Firestone, Senior Technical Editor SAIC General Sciences Corporation, BeltsviIIe, Maryland Volume 11, SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3 John E. O'Reilly NOAA, National Marine Fisheries Service, Narragansett, Rhode Island St6phane Maritorena, Margaret C. O'Brien, David A. Siegel, Dierdre Toole, David Menzies, and Raymond C. Smith University of California at Santa Barbara, Santa Barbara, California James L. Mueller CHORS/San Diego State University, San Diego, California B. Greg Mitchell and Mati Kahru Scripps Institution of Oceanography, San Diego, California Francisco P. Chavez and P. Strutton Monterey Bay Aquarium Research Institute, Moss Landing, California Glenn F. Cota Old Dominion University, Norfolk, Virginia Stanford B. Hooker and Charles R. McClain NASA Goddard Space Flight Center, Greenbelt, Maryland Kendall L. Carder and Frank Mtiller-Karger University of South Florida, St. Petersburg, Florida Larry Harding and Andrea Magnuson Horn Point Laboratory, Cambridge, Maryland David Phinney Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, Maine Gerald F. Moore and James Aiken Plymouth Marine Laboratory, Plymouth, United Kingdom Kevin R. Arrigo Stanford University, Stanford, California Ricardo Letelier Oregon State University, Corvallis, Oregon Mary Culver NOAA, Coastal Services Center, Charleston, South Carolina October 2000

Original page 4

ISSN 1522-8789 Available from: NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076-1320 Price Code: A17 National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Price Code: A10

Original page 5

O'Reilly et al. Table of Contents Prologue .................................................................................................1 1. OC2v2: Update on the Initial Operational SeaWiFS Chlorophyll a Algorithm .......................... 3 1.1 Introduction ......................................................................................... 3 3 1.2 The SeaBAM Data Set .............................................................................. 1.3 OC2v2 Algorithm .................................................................................... 7 1.4 Conclusions .......................................................................................... 8 2. Ocean Color Chlorophyll a Algorithms for SeaWiFS, OC2, and OC4: Version 4 ........................ 9 2.1 Introduction ........................................................................................ 10 2.2 The In Situ Data Set ............................................................................... 10 2.3 OC2 and OC4 ...................................................................................... 15 2.4 Conclusions ........................................................................................ 19 3. SeaWiFS Algorithm for the Diffuse Attenuation Coefficient, K(490), Using Water-Leaving ........... 24 Ra_iiances at 490 and 555 nm 3.1 Introduction ........................................................................................ 24 3.2 Data and Methods ................................................................................. 25 3.3 Results ............................................................................................. 25 3.4 Discussion .......................................................................................... 25 4. Long-Term Calibration History of Several Marine Environmental Radiometers (MERs) .............. 28 4.1 Introduction ........................................................................................ 28 4.2 ICESS Facility and Methods ........................................................................ 28 4.3 Results ............................................................................................. 33 4.4 Long-Term Averages ............................................................................... 41 4.5 Other Issues ........................................................................................ 43 4.6 Conclusions ........................................................................................ 45 GLOSSARY ...............................................................................................46 SYMBOLS ................................................................................................46 REFERENCES ............................................................................................ 47 THE SEAWIFS POSTLAUNCH TECHNICAL REPORT SERIES .............................................. 48

Original page 6

"2_

Original page 7

O'Reilly ABSTRACT et al. Volume II continuesthe sequentialpresentationof postlaunch data analysisand algorithm descriptionsbegun in Volume 9. Chapters I and 2 presentthe OC2 (version2) and OC4 (version4) chlorophylla algorithmsused in the SeaWiFS data second and thirdreprocessings,August 1998 and May 2000, respectively.Chapter 3 describes a revisionofthe K(490) algorithmdesignedto use water-leavingradiancesat 490 nm which was implemented for the third reprocessing.Finally,Chapter 4 isan analysisof in htu radiometer calibrationdata over severalyears at the Universityof California,Santa Barbara (UCSB) to establishthe temporal consistencyof theirin-water opticalmeasurements. PROLOGUE The SeaWiFS ProjectCalibrationand ValidationTeam SeaWiFS Bio-optical Algorithm Mini-workshop (SeaBAM) data set (the number of data sets, N = 919) which contains coincident in situ remote sensing reflectance, ]_, (CVT) is responsiblefor the overallquality of the data and in situ chlorophyll a, Ca, measurements from a variproducts and forverifyingthe processing code. The pre- ety of oceanic provinces. Following the SeaWiFS launch, launch quality control strategy was outlined in Volume 38 of the SeaWiFS Technical Report Series (Prelaunch). Since SeaWiFS began routine data processing in September 1997, the CVT has constantly worked to resolve data quality issues and improve on the initial data evaluation methodologies. These evaluations resulted in three major reprocessings of the entire data set (February 1998, August 1998, and May 2000). Each reprocessing addressed the data quality issues that could be identified up to the time of each reprocessing. The number of chapters (21) needed to document this extensive work in the SeaWiFS Postlaunch Technical Report Series requires three volumes: Volumes 9, 10, and 11. Volume tl continues the sequential presentation of postlaunch data analysis and algorithm descriptions, begun in Volume 9, by describing the algorithm improvements to two versions of the chlorophyll a algorithm and the revised diffuse attenuation coefficient algorithm at 490nm, K(490), developed for the third reprocessing. In addition, an analysis of radiometer calibration data at the University the accuracy of SeaWiFS chlorophyll a estimates using the OC2 algorithm was evaluated against new in situ measurements. These new data indicated that OC2 was performing generally well in Case-1 waters with Ca concentration, between 0.03-1 mgm -3, but tended to overestimate Ca at higher concentrations. To strengthen the SeaBAM data set at C'a > 1 mgm -3, 255 new stations were added to the original data set. These new data _enerally showed lower Rrs(490)/Rrs(555) band ratios at Ca > 4mgm -3 than in the original SeaBAM data set, which would explain some of the overestimations observed with OC2. The new SeaBAM data set was used to refine the coefficients for the OC2 modified cubic polynomial (MCP) function. The updated algorithm (OC2v2) is presented along with its statistical performance and a comparison with the original version of the algorithm. 2. Ocean Color Chlorophyll a Algorithms for SeaWiFS, 0C2, and 0C4: Version 4 This chapter describes the revisions (version 4) to the of California Santa Barbara (UCSB) is described, which es- ocean chlorophyll two- and four-band algorithms as well as tablishes the temporal consistency of their in-water optical measurements. It is expected that other improvements, including new geophysical data products, and updated algorithms will be developed in the future which will require additional reprocessings. The SeaWiFS Project Office will remain dedicated to providing better products and to the documentation of future analysis and algorithm improvement studies. A short synopsis of each chapter in this volume is given below. 1. 0C2v2: Update on the Initial Operational SeaWiFS Chlorophyll a Algorithm The original at-launch SeaWiFS algorithm (OC2 for Ocean Chlorophyll 2-band algorithm) was derived from the the very large in situ data set used to update these algorithms for use in the third reprocessing of SeaWiFS data. The in situ data set is substantially larger (N = 2,853) than was used to develop earlier versions of OC2 and OC4. The data set includes samples from a greater variety of biooptical provinces, and better represents oligotrophic and eutrophic waters. The correlation between chlorophyll a concentration, Ca, estimated using OC4 and in situ Ca (Ca) estimated from fluorometric and high performance liquid chromatography (HPLC) analyses was slightly higher than that for OC2. OC4 would be expected to perform better than OC2, when applied to satellite-derived, waterleaving radiances retrieved from oligotrophic and eutrophic areas. Variations of the OC4 algorithm are provided for other ocean color sensors to facilitate comparisons with SeaWiFS.

Original page 8

SeaWiFSPostlaunchCalibration 3. SeaWiFS Algorithm for the Diffuse Attenuation Coefficient, K(490), Using Water-Leaving Radiances at 490 and 555nm A new algorithm has been developed using the ratio of water-leaving radiances at 490 and 555 nm to estimate K(490), the diffuse attenuation coefficient of seawater at 490nm. The standard uncertainty of prediction for the new algorithm is statistically identical to that of the Sea- WiFS prelaunch K(490) algorithm, which uses the ratio of water-leaving radiances at 443 and 490nm. The new algorithm should be used whenever the uncertainty of the 443 Barbara (UCSB) during the Bermuda Bio-Optics Project SeaWiFS determination of water-leaving radiance at is larger than that at 490 nm. 4. Long-Term Calibration History of Several Marine Environmental Radiometers (MERs) The accuracy of upper ocean apparent optical properties (AOPs) for the vicarious calibration of ocean color in methods used here to examine stability accommodate the satellites ultimately depends on accurate and consistent situ radiometric data. The Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) project is charged with providing estimates in- bration coefficients accordingly. This analysis may serve as of normalized water-leaving radiance for the SeaWiFS and Validation Analyses, Part 3 an absolute accuracy of 3%. This chapter is a report on the analysis and reconciliation of the laboratory calibration history for several Biospherical Instruments (BSI) marine environmental radiometers (MERs), models MER-2040 and -2041, three of which participate in the SeaWiFS Calibration and Validation Program. This analysis includes data using four different FEL calibration lamps, as well as calibrations performed at three SeaWiFS Intercalibration Round-Robin Experiments (SIRREXs). Barring a few spectral detectors with known deteriorating responses, the radiometers used by the University of California, Santa (BBOP) have been remarkably stable during more than five years of intense data collection. Coefficients of variation for long-term averages of calibration slopes, for most detectors in the profiling instrument, were less than 1%. Long-term averages can be applied to most channels, with deviations only after major instrument upgrades. The addition of new calibration data as they become available. This enables researchers to closely track any changes in the performance of these instruments and to adjust the calistrument to within 5%. This, in turn, demands that the ra- a template for radiometer histories which will be cataloged diometric stability of in situ instruments be within 1% with by the SIMBIOS Project.

Original page 9

O'Reillyet al. Chapter 1 OC2v2: Update on the Initial Operational SeaWiFS Chlorophyll a Algorithm STEPHANE MARITORENA ICESS/University of California at Santa Barbara Santa Barbara, California JOHN E. O'REILLY NOAA National Marine Fisheries Service Narragansett, ABSTRACT Rhode Island The original at-launch SeaWiFS algorithm (OC2 for Ocean Chlorophyll 2-band algorithm) was derived from the SeaBAM data set (N = 919) which contains coincident remote sensing reflectance, /}rs, and in situ chlorophyll a, Ca, measurements from a variety of oceanic provinces. Following the SeaWiFS launch, the accuracy of SeaWiFS chlorophyll a estimates using the OC2 algorithm was evaluated against new in situ measurements. These new data indicated that OC2 was performing generally well in Case-1 waters with Ca concentration, between 0.03-1 mgm -a, but tended to overestimate (a at higher concentrations. To strengthen the SeaBAM data set at Ca > 1 mgm -3, 255 new stations were added to the original data set. These new data generally showed lower Rrs(490)/R,s(555) band ratios at C'a > 4mgm -3 than in the original SeaBAM data set, which would explain some of the overestimations observed with OC2. The new SeaBAM data set was used to refine the coefficients for the OC2 MCP function. The updated algorithm (OC2v2) is presented along with its statistical performance and a Comparison with the original version of the algorithm. 1.1 INTRODUCTION The at-launch SeaWiFS chlorophyll a algorithm, named OC2 for Ocean Chlorophyll 2-band algorithm, is an empirical equation relating remote sensing reflectances, Rrs, in the 490 and 555nm bands to chlorophyll a concentration, Ca (O'Reilly et al. 1998). OC2 was derived from a large data set (N = 919) of coincident in situ remote sensing reflectance and chlorophyll a concentration measurements,/)rs(A) and Ca, respectively. This large data set covered a Ca range of 0.02-32 mg m -3 from a variety of oceanic provinces, and was assembled during SeaBAM. The main SeaBAM objective was to evaluate a variety of biooptical algorithms and produce an at-launch operational algorithm suitable for producing chlorophyll a images at global scales from SeaWiFS data (Firestone and Hooker 1998). The OC2 algorithm was chosen by the SeaBAM participants, because it represented a good compromise between simplicity and performance over a wide range of ca. The formulation of the OC2 algorithm is an MCP: Ca = 10 (a° + a,R2 + a2R + a3 R3) + a4, (1) 490 where R2 = log10(Rs55) and R_; is a compact notation for the Rrs(A_)/Rrs(Aj) band ratio. 1.2 The SeaBAM DATA SET While the SeaBAM data set (Fig. I) is a large, qualitycontrolled data set, it has several known limitations: 1. It is mostly representative of Case-l, nonpolar waters; 2. Data from very oligotrophic (Ca < 0-05mg m-3) and eutrophic (Ca > 3 mg m -3) areas are underrepresented; 3. The chlorophyll a concentration data are determined from both fluorometric and HPLC techniques; and 4. Because some of the/_rs(A) measurements were not exactly centered on the SeaWiFS wavelengths, radiometric adjustments were necessary (O'Reilly et al. 1998). Additionally, even though the SeaBAM data were quality controlled, there was still significant variability in the radiometric data (i.e., variations perpendicular to the xaxis in Fig. 1). This variability is partly natural, caused 3

Original page 10

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 10 I I I l 1111 I I I iOIli I I I Illll I I I I IIII " % ...... ,-- 0C2-" ÷ .i ÷ -*-----.;"...... i............... *.':"... 0.1 I I I IIIIh I I I I lllll I• I I 1 IIII1 I I I Illl 0.0 0.1 Ca (mg m -3) 1 10 100 • 555 versus the original SeaBAM data set (N = 919). The curve Fig. 1. A scatterplot of 5490 Ca for represents the OC2 algorithm 10.0 ,.jL'.'.' '''",..d, 9' ' ' '''" ' ' ''''" o'NewSeaBAM''dato'.... .:' __ "+_ , ............. o.,I.....,,,, i .... 0C2 - ".:. i_ oc_2 - -__- ........ ...................... --o%--..; .......:,,,....1 I I I I'::: l 0.01 O. 10 _ (rag m-3) 1.00 10.00 100.00 Fig. 2. A scatterplot of 549o"'sss versus Ca for the original SeaBAM (crosses) and the new data (circles). The dotted curve represents the original OC2 algorithm; the solid curve represents OC2v2, the new algorithm. 4

Original page 11

O'Reflly et al. 1oo__pE:, REDUCEb'M'OR:AXIS'..... F N:, 1174 .'_ / : r- INT: -0,0000 .-'" + 7 " i" S=I2OPE; !.0000 ..'" +# v" ,: lOk-r_i._ .......... :,.----.,-,,:+-d-----.,.-.-::- •. ....,]it L . o.,:J: 0.01 ..... "..... , ..................... , , ,,,,,o , . ,,,,,, , , ,,,,,, ,: ,,,,. 1°°I ,--, 10 °m 4.* t- (0 O 0.1 0.01 i i iiiiii i i iiiiii i i IIIIH i i iiiii 0.01 0.1 1 10 100 0.01 0.1 1 10 100 ca (g rl) 170 N: 1174 153 MIN: -0.753 MAX: 0.872 136 MED: -0.003 MEAN: -0.000 STD: 0.196 119 SKEW: 0°034 KURT: 1.511 ., 102 85 ¢. 51 34 17 0 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 I°g(Ca Ca ) 100 10 I • .t ¸¸ :.. o) 1 0.1 +÷ e) ++- 0.01 0.1 1.0 10.0 Fig. 3. Comparisons between OC2v2 (modeled) Ca Quantiles (_g 1-1) I ,11 _11 _11111 i i willn _ r r_TTVln N= 1174 --% d) 1.00 0.01 0.1 1 10 100 ca (_g,-1) Ca values and (in situ) Ca data: a) scatterplot of Ca versus Ca; b) quantile-quantile plot of Ca versus Ca; c) frequency distribution of log(Ca/Ca); d) relative frequency of Ca (thin solid curve) and Ca (thick gray curve); e) Rsss49°versus Ca. Also shown is the OC2v2 model (solid curve).

Original page 12

SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3 Table 1. Data sources and characteristics of the combined SeaBAM data set. The BBOP data sets were taken monthly, and the California Cooperative Fisheries Institute (CalCOFI) data sets were taken quarterly. NF is the number fluorometric chlorophyll a sets, and NH is the number of HPLC chlorophyll a sets. The last six subsets are the new data that were added to the original SeaBAM data. Data Set Provider Location Date(s) N NF NH Wavelengths BBOP92-93 D. Siegel 1992-1993 72 72 72 :4i'() 441 488 520 565 665 Sargasso Sea BBOP94-95 D. Siegel Sargasso Sea 1994-1995 67 61 67 410 441 488 510 555 665 WOCE 50°S-13°N, Mar93 70 70 410 441 488 520 565 665 J. Marra 88 91°W 10°S-30°N, Apr94 18-37°W EqPac Mar92, Sept92 t26 126 410 441 488 520 550 683 :C. Davis 0 °, 140°W May89 72 72 412 441 488 521 550 NABE C. Trees 46-59°N, 17-200W Apt89 40 40 410 441 488 520 550 683 NABE IC. Davis 46°N, 19°W Aug91 87 87 412 443 490 510 555 670 Carder K. Carder N. Atlantic Pacific Ju192 Gulf of Mexico Apr93 Arabian Sea Nov94, Jun95 Aug93-Sept96 303 303 412 443 490 510 555 665 CalCOFI G. Mitchell Calif. Current Sept92 8 8 8 412 443 490 510 555 MOCE-1 D. Clark Monterey Bay Apt93 5 5 5 !412 443 490 510 555 MOCE-2 D. Clark Gulf of Calif. i i North Sea R. Doerffer 55-52°N, 0-8°E Jul94 10 10 ]412 443 490 510 555 670 Chesapeake Bay Apr95 and 9 9 412 443 490 510 555 671 L. Harding 37°N, 75°W Aug96 8 8 412 443 490 509 555 665 Canadian Arctic G. Cota 74.38°N, 95°W Sept95 and 42 42 33 412 443 490 510 555 AMT-1 S. Hooker 50°N-50°S, AMT-2 G. Moore 0-60°W Ju195 Apt96 MBARI F. Chavez 9°N-9°S, Oct97-Dec97 34 34 412 443 490 510 555 670 120-180°W Sept97-Jan98 35 35 412 443 490 510 555 670 COASTS G. Zibordi 45.3°N, 12.5°E May96-Aug97 14 14 5 412 443 490 510 555 670 CARIACO F. Miiller- 10.3°N, Karger 64.4°W Sept97-Jun98 82 82 412 443 490 510 555 670 AMT-5 S. Hooker 50°N-50°S, AMT-6 S. Hooker 20°E-60°W ROAVERRS 96-97 K. Arrigo Ross Sea Dec97-Jan98 67 67 412 443 490 510 555 670 May97-Nov97 23 22 15 412 443 490 510 555 CSC M. Culver 30-35°N, 76-82°W 1. BBOP: Bermuda Bio-Optical Prfiler 2. WOCE: World Ocean Circulation Experiment 3. EqPac: Equatorial Pacific (Process Study) 4. NABE: North Atlantic Bloom Experiment 5. CaICOFI: California Cooperative Fisheries Institute 6. MOCE: Marine Optical Characterization Experiment 7. AMT: Atlantic Meridional Transect 8. MBARI: Monterey Bay Aquarium Research Institute 9. COASTS: Coastal Atmosphere and Sea Time Series .... Total 1174 759 613 10. ROAVERRS: Research on Ocean-Atmosphere Variability and Ecosystem Response in the Ross Sea 11. CSC: Coastal Services Center (NOAA)

Original page 13

O'Reillyet al. _00 ,' i I I lllll i I I B III I I I i IIII I / I I I Ill " 0 ........................................... 2 g I 0.01 , , ,LA ,,' , , '''_H' , _ ,,,,,,; i , _i,,' 0.01 0.1 I 10 100 initial Algorithm Ca (rag m -3) Fig. 4. Statistical and graphical comparisons of the OC2 and OC2v2 algorithms. The thick solid curve illustrates how both algorithms compare in the 0.01-100 mg m -3 Ca concentration range (when the same R490555 ratios are used for both equations). The 1:1 (center), 1:5 (bottom), and 5:1 (top) lines are also plotted. by the bio-optical variability among the different oceanic provinces sampled (e.g., variation in phytoplankton species, relative concentration, and the influence of accessory pigments or the physiological state of phytoplanktonic cells, etc.), but some of this radiometric variability results from differences in methodologies, instrument designs, calibrations, data processing, and environmental conditions (sea and sky state). 1.3 OC2v2 ALGORITHM Since the SeaBAM workshop, new in situ measurements have become available and were used to test the accuracy of the OC2 algorithm. These new data indicated that OC2 was performing generally well (within the +35% accuracy) in Case-1 waters with Ca between 0.03- 1 mgm -3, but at chlorophyll a concentrations exceeding 2- 3mgm -3, OC2 tended to overestimate (a. This tendency was also apparent in SeaWiFS chlorophyll retrievals from some offshore, chlorophyll-rich waters, where ample historical sea-truth data suggest that the frequency of these high SeaWiFS chlorophyll retrievals are improbable. As indicated above, the SeaBAM data set contains relatively few chlorophyll a measurements above 2mgm -3. Moreover, those above 2 mg m -3 are from a limited number of regions and may not adequately represent the full range of bio-optical variability expected in chlorophyll-rich waters. To strengthen the SeaBAM data set at Ca > are illustrated in Table 1 and Fig. 2. Note that not all new data are from chlorophyll-rich waters. Nevertheless, all available new data were used to form the combined set, because these new sources increase the bio-optical diversity of the data set. Among these new data, the highest chlorophyll concentrations come from the ROAVERRS 96-97 and AMT-6 surveys. It is important to note the R'490 band ratios measured during these two surveys, at 555 Ca > 4mgm -3, are substantially lower than the lowest band ratios present in the original SeaBAM data (Fig. 2). The dispersion of the combined data is greater than in the original SeaBAM data set, particularly at chlorophyll values exceeding 2 mgm -3. This increased dispersion is expected at high Ca values, because some of these data come from near-shore coastal locations and may be influenced by various optically active components other than phytoplankton [colored dissolved organic matter (CDOM), sediments, nonbiogenous detrital substances, etc]. It is clear from Fig. 2 that the original SeaBAM data set did not adequately encompass the range of variability in h 9° band ratios present in chlorophyll-rich waters, and that OC2 derived from SeaBAM would overestimate chlorophyll a for many of the new observations with Ca > 2mgm -3. Assuming the combined data shown in Fig. 2 are an improved representation of the natural variability present in productive oceanic and coastal zones, the combined data set was used to refine the OC2 functional coeffil mgm -3, 255 new measurements of flag0 and Ca were cients. Because the underlying assumptions and appropri- "_555 added to the original SeaBAM data set. Characteristics of ateness for using the MCP function remain valid (O'Reilly the combined data (original SeaBAM data and new data) et al. 1998), other formulations were not explored. The

Original page 14

SeaWiFS Postlaunch Calibrationand Validation Analyses,Part 3 updated algorithm (OC2v2) isas follows: U. = 10 (0.2974 - 2.2429R2 + 0.8358P_ - 0.0077/_) _ 0.0929 (2) where R2 is defined as in (1). Statistical and graphical comparisons between chlorophyll a concentrations derived from OC2v2 versus Ca are presented in Fig. 3. A comparison of the output from OC2 and OC2v2 is illustrated in Fig. 4. OC2 and OC2v2 yield very similar results for Co ranging between 0.03- 1.5mgm -3. At chlorophyll a values exceeding 3mgm -s, OC2v2 estimates are substantially lower than OC2. At very low chlorophyll a concentrations, 0.01-0.02 mg m -3, OC2v2 produces slightly higher concentrations than 0C2. 1.4 CONCLUSIONS While, on average,OC2v2, should resultin an improvement over OC2 in chlorophyll-richareas,the uncertainties remain largeforC',> 3-4 mg m -3. It must be emphasized limitationsof the originalSeaBAM data set remain valid for the new combined data. More good quality ]_rs(A) and U, data are needed from regions with chlorophylla concentrationsabove 3.0 and below 0.04mg m -3 to better characterizethe bio-opticalvariabilityof these waters and, thus, to identifypotentialstrategiesto achievereasonable satellitechlorophylla retrievals. ACKNOWLEDGMENTS The authorswish to thank allthe participantsofthe SeaBAM workshop fortheirhelpand contributionto thedata set:K.L. Carder, S.A. Garver, S.K. Hawes, M. Kahru, C.R. McClain, B.G. Mitchell,G.F. Moore, J.L.Mue!ler,B.D. Schi'eber,and D.A. Siegel.We alsowould liketo acknowledgeJ.Aiken,K.R. Arrigo,F.P.Chavez,D.K. Clark,G.F. Cot°,M.E. Culver,C.O. that because the variabilityof the data increasesat high Davis,R. Doerffer,L.W. Harding,S.B.Hooker,J.Marra, F.E. concentrations,the precisionof the SeaWiFS retrievalsis Mfiller-Karger,A. Subramaniam, C.C. Trees,and G. Zibordi that the who kindlyprovidedsome oftheirdata. inevitablydegraded. It must alsobe kept in mind 8

Original page 15

O'Reilly et al. Chapter 2 Ocean Color Chlorophyll a Algorithms for SeaWiFS, OC2, and OC4: Version 4 JOHN E. O'REILLY NOAA, National Marine Fisheries Service, Narragansett, Rhode Island STEPHANE MARITORENA, DAVID A. SIEGEL, MARGARET C. O'BRIEN, AND DIERDRE TOOLE ICESS/University of California Santa Barbara, Santa Barbara, California B. GREG MITCHELL AND MATI KAHRU Scripps Institution of Oceanography, University of California, San Diego, California FRANCISCO P. CHAVEZ AND P. STRUTTON Monterey Bay Aquarium Research Institute, Moss Landing, California GLENN F. COTA Old Dominion University, Norfolk, Virginia STANFORD B. HOOKER AND CHARLES R. MCCLAIN NASA Goddard Space Flight Center, Greenbelt, Maryland KENDALL L. CARDER AND FRANK MOLLER-KARGER University of South Florida, St. Petersburg, Florida LARRY HARDING AND ANDREA MAGNUSON Horn Point Laboratory, University of Maryland, Cambridge, Maryland DAVID PHINNEY Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, Maine GERALD F. MOORE AND JAMES AIKEN Plymouth Marine Laboratory, Plymouth, United Kingdom KEVIN R. ARRIGO Department of Geophysics, Stanford University, Stanford, California RICARDO LETELIER College of Oceanic and Atmospheric MARY Sciences, Oregon State University CULVER NOAA, Coastal Services Center, Charleston, South Carolina ABSTRACT This chapter describesthe revisions(version4) to the ocean chlorophylltwo- and four-band algorithms,as well as the very large in situdata setused to update these algorithms foruse in the third reprocessingof SeaWiFS data. The in situdata set issubstantiallylarger(N = 2,853) than was used to develop earlierversionsof OC2 and OC4. The data set includessamples from a greatervarietyof bio-opticalprovinces,and better represents oligotrophicand eutrophic waters. The correlationbetween chlorophylla concentration,Ca, estimated using OC4 and in situCa (Ca) estimated from fluorometricand HPLC analyses was slightlyhigher than that for OC2. OC4 would be expected to perform better than OC2, when applied to satellite-derived,water-leavlng radiances retrievedfrom oligotrophicand eutrophic areas. Variationsof the OC4 algorithm are provided for other ocean colorsensorsto facilitatecomparisons with SeaWiFS.

Original page 16

SeaWiFS Postlaunch Calibration 2.1 INTRODUCTION The accuracy, precision, and utility of an empirical ocean color algorithm for estimating global chlorophyll and Validation Analyses, Part 3 2.2 THE IN SITU DATA SET A very large data set of/rs() and Ca measurements a were assembled for the purpose of updating ocean color distributions depends on the characteristics of the algo- chlorophyll algorithms for SeaWiFS calibration and valirithm and the in situ observations used to develop it. The empirical pigment and chlorophyll algorithm widely used in the processing of the global Coastal Zone Color Scandation activities. The data sets and the principal investigators responsible for collecting the data are provided in Table 2. Table 3 gives the location and acquisition time pener (CZCS) data set was developed using fewer than 60 riods of the data, along with an indication of the number in situ radiance and chlorophyll a pigment observations (Evans and Gordon 1994). Since the CZCS period, a number of investigators have measured in situ remote sensing reflectance, Rrs(,k), and in situ chlorophyll a concentraof observations, how the chlorophyll a concentration was determined (fluorometry or HPLC), and how the radiometric observations were made (above- or in-water). The wavelengths of the latter are presented in Table 4. tion, Ca, from a variety of oceanic provinces. In 1997, the The data set has a total of 2,853 in situ observations. It SeaBAM group (Firestone and Hooker 1998) assembled large Rrs(A) and Ca data set containing 919 observations. This data set was used to evaluate the statistical performance of chlorophyll a algorithms and to develop the ocean chlorophyll 2-band (OC2) and ocean chlorophyll 4-band (OC4) algorithms (O'Reilly et al. 1998). OC2 predicts Ca from the Rrs(490)/Rrs(555) band ratio a is the largest ever assembled for algorithm refinement, and represents a large diversity of bio-optical provinces. The Ca data are derived from a mixture of HPLC and fluorometric measurements from surface samples: 28% and 72% of the data, respectively (Table 3). The Ca values range from 0.008-90 mg m -3. The relative frequency distribution of Ca has a primary and secondary peak at 0.2mgm -3 using an MCP formulation. Hereafter, the Rr_ ratio con- and approximately l mgm -3, respectively (Fig. 5). Ocestructed from band A divided by band B is indicated by R_, i.e., the Rrs(490)/Rrs(555) band ratio is represented by 490• 555" OC4 also relates band ratios to chlorophyll a with a single polynomial function, but it uses the maximum band ratio (MBR) determined as the greater of the 443_555, R49o555, Or 51o_555 values. OC2 was employed as the standard chlorophyll a algorithm by the SeaWiFS Project following the launch of SeaWiFS in September 1997. Although the statistical characteristics of OC4 were superior to those of OC2, the SeaBAM group recommended using the simpler 2-band OC2 at launch. With the goal of improving estimates in chlorophyllrich waters, OC2 was revised (version 2) based on an expanded data set of 1,174 in situ observations (Maritorena and O'Reilly 2000) and applied by the SeaWiFS Project in the second data reprocessing (McClain 2000). Additional in situ data have become available as the result of new programs (e.g., SIMBIOS) and the continuation and expansion of ongoing field campaigns. These new data increase the variety of bio-optical provinces represented in the original data set and fill in regions of the Rr(A) and Ca domain which were not previously well represented. Also, results from over 2.5 years of SeaWiFS data are now available to assess the overall performance of the SeaWiFS instrument and identify areas where improvements are needed in the processing of satellite ocean color data (McClain 2000). An update to the OC2 and OC4 chlorophyll algorithms a measurements of /rs(555) and /rs(565) from 1994-1995 for SeaWiFS are presented in this chapter, along with situ BBOP surveys (equation 2 from O'Reilly et al. 1998). The description of the major features of the very large in of Rr(555) value for the CB-MAB subset was computed by data set used to refine these models, and a comparison the updated algorithms with earlier versions MBR chlorosen- value was estimated from the Rrs(520) values for the Eqphyll algorithms for several other satellite ocean color sors are also provided to facilitate intercomparisons with SeaWiFS. 10 anic regions with Ca between 0.08-3 mg m -3 are relatively well represented. There are 238 observations of Ca exceeding 5mgm -3 and 116 observations with Ca less than 0.05mgm -3. A comparison of the Ca frequency distribution with those from previous versions (O'Reilly et al. 1998 and Maritorena and O'Reilly 2000) shows that. oligotrophic and eutrophic waters are relatively better represented in the current data set. The present data set also has a more equitable distribution over a broader range of Ca (i.e., 0.08-3mgm-3). Measurements of RCs(),) were made using both aboveand in-water radiometers: 88% and 12% of the data, respectively (Table 3). In several subsets, multiple R_s measurements were taken at stations where only a single Ca measurement was made. For these subsets (BBOP9293, WOCE, EqPac, NABE, GoA97, Ber96, Bet95, Lab97, Lab96, Res96, Res95-2, Res94), the median Rrs value was paired with the solitary Ca observation and added to the data set. Except in a limited number of circumstances, band ratios determined from the median Rrs values agreed well with the individual band ratios. Several subsets, however, required adjustments to the/()) values to conform with the SeaWiFS band set. The R(555) value was estimated from the /_rs(565) measurement for the BBOP9293 and WOCE data using an equation derived from concurrent averaging the/_rs(550) and/_rs(560) values. The/_rs(510) Pac, WOCE, NABE, and BBOP9293 data sets using the following conversion equation based on Morel and Maritor-

Original page 17

O'Reillyet al. Table 2. Thedatasetsandthe investigatorsresponsibleforthe datacollectionactivity. No. Data Set Investigators 1 ROAVERRS 96-97 Arrigo, K. 2 CARDER Carder, K. 3 CARDER Carder, K. 4 CARDER Carder, K. 5 CARDER Carder, K. 6 MF0796 Carder, K. 7 TOTO Carder, K. 8 CoBOP Carder, K., J. Patch 9 EcoHAB Carder, K., J. Patch 10 Global Chavez, F. 11 MBARI EqPac Chavez, F., P. Strutton 12 MOCE-1 Clark, D. 13 MOCE-2 Clark, D. 14 MOCE-4 Clark, D., C. Trees 15 GoA97 Cota, G. 16 Ber95 Cota, G., S. Saitoh 17 Bet96 Cota, G., S. Saitoh 18 Lab96 Cota, G., G. Harrison 19 Lab97 Cota, G., G. Harrison 20 Res94 Cota, G. 21 Res95-2 Cota, G. 22 Res96 Cota, G. 23 Res98 Cota, G. 24 CSC Culver, M., A. Subramaniam 25 CSC Culver, M., A. Subramaniam 26 CSC Culver, M., A. Subramaniam 27 EqPac Davis, C. 28 NABE Davis, C. 29 CB-MAB Harding, L., A. Magnuson 3O AMT-1 Hooker, S., G. Moore 31 AMT-2 Moore, G., S. Hooker 32 AMT-3 Hooker, S., J. Aiken, S. Maritorena 33 AMT-4 Hooker, S., S. Maritorena 34 AMT-5 Hooker, S., S. Maritorena 35 AMT-6B Moore, G., S. Hooker, S. Maritorena 36 AMT-6 Hooker, S., S. Maritorena 37 AMT-7 Hooker, S., S. Maritorena 38 AMT-8 Hooker, S., S. Maritorena 39 HOT Letelier, R., R. Bidigare, D. Karl 40 WOCE Marra, J. 41 WOCE Marra, J. 42 CalCOFI Mitchell, G., M. Kahru 43 CalCOFI Mitchell, G., M. Kahru 44 RED9503 Mitchell, G., M. Kahru 45 AI9901 Mitchell, G., M. Kahru 46 JES9906 Mitchell, G., M. Kahru 47 CARIACO M/iller-Karger, F., R. Varela, J. Akl, A. Rondon, G. Arias 48 NEGOM M/iller-Karger, F., C. Hu, D. Biggs, B. Nababan, D. Nadeau, J. Vanderbloemen 49 ORINOCO M/iller-Karger, F., R. Varela, J. Akl, A. Rondon, G. Arias 50 GOIvI Phinney, D., C. Yentch 51 Arabian Sea Phinney, D., C. Yentch 52 FL-Cuba Phinney, D., C. Yentch 11

Original page 18

SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3 Table 2. (cont.) The data sets and the investigators responsible for the data collection activity. No. Data Set Investigators 53 BBOP 9293 Siegel, D., M. O'Brien, N. Nelson, T. Michaels 54 BBOP 9499 Siegel, D., M. O'Brien, N. Nelson, T. Michaels 55 Plumes & Blooms Siegel, D., D. Toole, L. Mertes, R. Smith, L. Washburn, M. Brzezinski 56 NABE Trees, C. 57 COASTS Zibordi, G. Table 3. Data sources, locations, and acquisition dates (summarized by the three-letter month abbreviation and the two-digit year) of the global data set. N is the number of samples, the Ca column indicates the method(s) used for chlorophyll a determination (F for fluorometry and H for HPLC), and the R¢8 column indicates the type of radiometric used for measuring remote sensing reflectance (A for above water and B for below water). No. Data Set Location 1 ROAVERRS 96--97 Ross Sea 2 CARDER North Atlantic 3 CARDER. Pacific 4 CARDER Gulf of Mexico 5 CARDER Arabian Sea 6 MF0796 Bering Sea 7 TOTO Bahamas 8 CoBOP Bahamas 9 EcoHAB W. Florida Shelf 10 Global Global 11 MBARI EqPac Equatorial Pacific 12 MOCE-1 Monterey Bay 13 MOCE-2 Gulf of California 14 MOCE-4 Hawaii 15 GoA97 Gulf of Alaska 16 Ber95 Bering Sea 17 Ber96 Bering Sea 18 Lab96 Labrador Sea 19 Lab97 Labrador Sea 20 Res94 Resolute 21 Res95-2 Resolute 22 Res96 Resolute 23 Res98 Resolute 24 CSC Onslow Bay and S. MAB 25 CSC S. Mid-Atlantic Bight 26 CSC Gulf of Mexico 27 EqPac 0°N,140°W 28 NABE 46°N,19°W 29 CB-MAB Chesapeake Bay and MAB South Atlantic Sep-Oct95 23 F B 30 AMT-I E. North Atlantic and W. South Atlantic Apt-May96 19 F B 31 AMT-2 E. North Atlantic and W. South Atlantic Sep-Oct96 20 H B 32 AMT-3 E. North Atlantic and W. South Atlantic Apt-May97 21 H B 33 AMT-4 E. North Atlantic and W. South Atlantic Sep-Oct97 45 H B 34 AMT-5 E. North Atlantic and W. South Atlantic Apr-May98 62 H B 35 AMT-6B E. North Atlantic and W. South Atlantic May-Jun98 35 H B 36 AMT-6 E. North Atlantic and E. South Atlantic Sep-Oct98 52 H B 37 AMT-7 E. North Atlantic and W. South Atlantic May-Jun99 46 H B 38 AMT-8 E. North Atlantic and W. 39 HOT N. Pacific Subtropical Gyre 40 WOCE 50°S-13°N,88-91°W 12 Dates N Ca Rrs Dec97-Jan98 73 H B Aug91 87 F A Jul92 F A Apr93 F A Nov94, Jun95 F A Apr96 22 F A Apr98, Apr99 26 F A May98, May-Jun99 43 F A Mar99-Mar00 (6 Surveys) 57 F A Nov93-Ju198 (18 Surveys) 284 F B Oct97-Nov99 (6 Surveys) 89 F B Sep92 8 H B Apr93 5 H B Jan-Feb98 20 F B Oct97 I0 F B Ju195 17 F B Ju196 16 F B Oct-Nov96 68 F B May-Jun97 71 F B Aug94 9 F B Aug95 14 F B Aug96 11 F B Aug98 91 F B May97 12 F B Sep97, Nov97, Apr98, Feb99 45 F B Apr99 6 F B Mar92, Sep92 36 H B Apt89 6 H B Apr96--Oct98 (9 Surveys) 197 H B (ALOHA) Feb98-May99 5O H,F B Mar-Apr93 15 F B

Original page 19

O'Reillyet al. Table 3. (cont.) The data sources, locations, and acquisition dates of the global data set. No. Data Set Location 41 WOCE 10°S-30°N,18-37°W 42 CaICOFI California Coast 43 CaICOFI California Coast 44 RED9503 California Coast (Red Tide) 45 AI9901 Subtrop. Atlantic, Indian Ocean 46 JES9906 E. Japan Sea 47 CARIACO Cariaco Basin 48 NEGOM NE Gulf of Mexico Orinoco Plume Jun98, Oct98, Feb99, Oct99 48 F A 49 ORINOCO Orinoco Delta, Paria Gulf, 50 GOM Gulf of Maine 51 Arabian Sea Arabian Sea 52 FL-Cuba Florida-Cuba 53 BBOP 9293 Sargasso Sea (BATS) 54 BBOP 9499 Sargasso Sea (BATS) 55 Plumes & Blooms Santa Barbara Channel 56 NABE 46-59°N,17-20°W 57 COASTS N. Adriatic Sea Table 4. The wavelengths of the radiometer data. Dates N Ca Rrs Apt-May94 27 F B 93-97 (16 Surveys) 299 F B 97-99 (6 Surveys) 100 F B Mar95 9 F B Jan-Mar99 36 F B Jun-Ju199 37 F B May96-Aug99 35 F A Jul-Aug98 13 F A Mar95-Apr99 (11 Surveys) 92 F C Ju195, Sep95, Oct95 15 F C Mar99 13 F C 92-93 30 H B Jan94-Aug99 83 H B Aug96-June99 251 F B May89 19 H B Sep97-Jan98 35 H B No. Data Set Nominal Center Wavelengths [nm] 1 ROAVERRS 96-97 412 443 490 510 555 655 2 CARDER 412 443 490 510 555 670 3 CARDER 412 443 490 510 555 670 4 CARDER 412 443 490510 555 670 5 CARDER 412 443 490510 555 670 6 MF0796 412 443 490 510 555 670 7 TOTO 412 443 490510 555 670 8 CoBOP 412 443 490 510 555 670 9 EcoHAB 412 443 490 510 555 670 10 Global 412 443 490 510 555 656 665 11 MBARI EqPac 412 443 490 510 555 670 12 MOCE-1 412 443 490 510 555 13 MOCE-2 412 443 490 510 555 14 MOCE-4 412 443 490 510 555 670 15 GoA97 405 412 443 490 16 Ber95 412 443 490 17 Ber96 405 412 443 490 18 Lab96 405 412 443 490 19 Lab97 405 412 443 490 20 Res94 412 443 490 510 520 532 555 565 619 665 683 700 510 555 665 683 510 520 532 555 565 619 665 683 700 510 520 532 555 565 619 665 683 700 510 520 532 555 565 619 665 683 700 510 555 665 683 21 Res95-2 412 443 490 510 555 665 683 22 Res96 405 412 443 490 510 520 532 555 565 619 665 683 700 23 Res98 405 412 443 490 510 520 532 555 565 619 665 683 700 24 CSC 380 412 443 490 25 CSC 380 412 443 490 26 CSC 380 412 443 490 27 EqPac 410 441 488 28 NABE 410 441 488 29 CB-MAB 412 443 455 490 30 AMT-1 412 443 490 31 AMT-2 412 443 490 510 555 683 510 555 683 510 555 683 520 550 683 520 550 683 510 532 550 560 589 625 671 683 700 510 555 665 510 555 665 13

Original page 20

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 Table4. (cont.) The wavelengths of the radiometer data. No. Data Set Nominal Center Wavelengths [nm] 32 AMT-3 412 443 490 510 555 665 33 AMT-4 412 443 490 510 555 665 34 AMT-5 412 443 490 510 555 665 35 AMT-6B 412 443 490 510 555 665 36 AMT-6 412 443 490 510 555 665 37 AMT-7 412 443 490 510 555 665 38 AMT-8 412 443 490 510 555 665 39 HOT 412 443 490 510 555 670 40 WOCE 410 441 488 41 WOCE 410 441 488 520 565 665 520 565 665 42 CalCOFI 340 380 395 412 443 455 490 510 532 555 570 665 43 CalCOFI 412 443 490 510 555 665 44 RED9503 340 380 395 412 443 455 490 45 AI9901 412 443 490 46 JES9906 412 443 490 47 CARIACO 412 443 490 48 NEGOM 412 443 490 49 ORINOCO 410 443 490 50 GOM 412 443 490 51 Arabian Sea 412 443 490 510 532 555 570 665 510 555 665 510 555 665 510 555 656 510 555 670 510 555 670 510 555 665 510 555 665 52 FL-Cuba 412 443 490 510 555 665 53 BBOP 9293 410 441 488 520 565 665 54 BBOP 9499 410 441 465 488 510 520 555 565 589 625 665 683 55 Plumes & 412 443 490 510 555 656 Blooms 56 NABE 412 441 488 57 COASTS 412 443 490 521 550 510 555 655 683 Global Data Set 0.90 .................... _ I o.8o .....................................i............_ :-:::::::::Tv_;i;,:ii_;;............- 0.8 ! ;:7 i 0.60 i .= 1; _ o0o ti; n- 0.30 0.20 ..................i.......... /: , J o ,'i I ........ - -.!v4;mu,.,. 0.6 E $ \ , iO. 2 :IV'. :\ - 0.10 .........._ ..-7-- i.............................................i ................................''':"!::_ ....................: 0.00 .,, ..-- ," ..... _ , , ,l[l,_ ......... ";=';";" ,',, 0.0 0.01 0.10 C a (mg m "3) 1.00 10.00 100.00 Fig. 5. The relative frequency distribution of Ca concentration in the in situ data used to develop versions 4 and earlier versions of the ocean chlorophyll algorithms (V1 is version 1, V2 is version 2, and V4 is version 4). The version 3 data set, an intermediate test set, is not described here). Relative frequency is the observed frequency normalized to the maximum frequency. 14

Original page 21

O'Reilly et al. ena (2000): Rrs(510) = Rrs(520)[1.0605321 - 0.1721619% + 0.0295192% 2 + 0.015062273 - 0.004133924"r_] (3) where % = log(Ca). association and a simple linear model is generally not the The Chesapeake Bay and Mid-Atlantic Bight (CB- best model to describe the band ratio Ca relationships over MAB) /_rs(),) measurements were corrected for the influ- the entire range of the data. ence of radiometer self-shading (Gordon and Ding 1992, and Zibordi and Ferrari 1995) using equations provided 2.3 OC2 AND OC4 by G. Zibordi. Corrections for radiometer shading by the Acqua Alta Oceanographic Tower were also applied to the the OC2 and OC4 Ca algorithms. Four observations, with COASTS/_rs(A) data (Zibordi et al. 1999). The CalCOFI, Ca greater than 64 mg m -z, were widely scattered in plots RED9503, and AI9901 data sets were also corrected for of band ratios versus Ca and were not used. A test verradiometer self-shading (Kahru and Mitchell 1998a and sion of the OC4 MBR model revealed 45 observations had 1998b.) log(Ca)/log(Ca) values exceeding three standard devia- Interpolated estimates of Rrs were also generated for tions, so these data were also discarded. The final model non-SeaWiFS wavelengths, which were not consistently coefficients were derived using the remaining 2,804 R_s and present in the global data set, to develop chlorophyll al- (a combinations. Algorithm refinement involved the degorithms similar to OC4 for use by other ocean color sentermination of model coefficients using iterative minimizasors. The interpolation-extrapolation method consisted of tion routines (using IDL) to achieve a slope of 1.000, an two steps. A cubic spline interpolation method [using the intercept of 0.000, minimum root mean square (RMS) er- Interactive Data Language (IDL)t, version 5.3] and four ror, and maximum R 2 between model and measured Ca measured adjacent R values were used to derive the interconcentration. The first version of OC4 (O'Reilly et al. polated R_s estimate (/rs). The interpolated values were 1998) was formulated as a modified cubic polynomial (i.e., then regressed against those measured Rr values present a third order polynomial plus an extra coefficient), howin the global data set; the resulting regresssion equation ever, the current version of 0C4 uses a fourth order poly- (Table 5) was applied in the second step to remove bias nomial (five coefficients), because this yielded better statisin the interpolated values. This scheme resulted in good tical agreement between model (Ca) and Ca than an MCP agreement between interpolated and measured Rrs over a formulation. An MCP equation was used to refine OC2 to wide range of chlorophyll concentration (Fig. 6). the same set of values (N=2,804) used to update OC4. The characteristics of the Rrs data most relevant to bio-optical algorithms are illustrated in Fig. 7. An impor- 4 (OC4v4), is: tant feature revealed by these plots is the dispersion of the data (variability is orthogonal to the major axis of the data). A pattern common to these plots is the progressive increase in dispersion with increasing chlorophyll concentration and decreasing band ratio. This is most evident The Rrs and Ca data (N=2,853) were used to revise The fourth order polynomial equation for OC4 version Ca = 10.0 (0.366 - 3.067R4s + 1.930R]s (4) + 0.649R3s - 1.532R_s) • _5_5 "s55 versus Ca. In addition to where R4s = lOgl0 [D443,_555 > 19490-555 > D510,_5551, where the arguin the plots of 19412 and _443 bio-optical variability, some of the scatter is caused by a ment of the logarithm is a shorthand representation for the variety of methodological errors (for example, surface ef- maximum of the three values. Hereafter, in an expression fects, ship shadow, and lower radiometric precision and such a R4s, the numerical part of the subscript refers to the extrapolation errors associated with measurements made number of bands used, and the letter denotes a code for the in turbid waters). specific satellite sensors IS is SeaWiFS, M is the Moderate Considering only the degree of scatter evident in these Resolution Imaging Spectroradiometer (MODIS), O is the plots, the z_443 provide the most precise (lowest disper- Ocean Color and Temperature Scanner (OCTS), E is the "_555 sion) Ca estimates at concentrations approximately less Medium Resolution Imaging Spectrometer (MERIS), and than 0.4mgm -3, whereas, the _51o and 1949o band ra- C is CZCS]. The modified cubic polynomial equation for "_555 "_555 OC2 version 4, hereafter referred to as OC2v4, is: tios would provide relatively more precise estimates of Ca in chlorophyll-rich waters. Over the entire data domain, R49055s yields the highest correlation with Ca, R 2 = 0.862 (Fig. 7), followed by 19443_555, R 2 = 0.847. It must be kept in mind, however, that R 2 is an index of the degree of linear where R2s = logm V 555]t IDL is a software product of Research Systems, Inc., Boulder, Ca = 10.0 (0"319 - 2.336R2s + 0.879R2_s (5) - 0.135R3s) - 0.071 t'D490 The statistical and graphical characteristics of these Colorado. two algorithms are illustrated in Figs. 8 and 9. The R 2 15

Original page 22

SeaWiFSPostlaunchCalibration 1.20 1.10 1.00 0.90 0.80 + and Validation Analyses, Part 3 " i+ _ +_ b 1.10 + + - 12o 1 0.80| N=350 t 0.01 0.10 1.00 10.00 IO0.O0 0.01 0.10 1.00 10.00 100.00 Ca(mg m"a) 1 20! r l ' C) 0.00 1.00 0,80 Ca (mg m3) ' '" i;, tN\ 258 j 0.01 0.10 1,00 10.00 100.00 0.01 0,10 1.00 10.00 100.00 C a (rag m_ 1,20 1.10 1.00 0.90 + 0.80 Ca (mg m_) 1.20j . 11o_ . 'q °:;I,,.,o,. U 0.01 0.10 1.00 10.00 100.00 0.01 0.10 1.00 10.00 100.00 C a (rag m) 1.201 + Q_ 1.101" Ca (rag m") , -,l=k,',...4z- °1 .... i+ ,F,EBIr -,-' '0C 0.90 ' .... " t 0.80iN=350 . 0.01 0.10 , . 1.00 10.00 100.00 Ca (rag m"s) Fig. 6. The ratio of Rrs based on interpolated Rrs (/) to measured R _(R) versus chlorophyll concentration (Ca): a)/_510:Rslo; b)/520:R520; c)/t531:R531; d)/550:R550; e) R555:R55s; f)/5_o:Rs60; and g) /6:R_85 E .-.:. :. -- __'" • ":!4.,1. . _ 1..- -. °:ii"R20,79 0 0.1 1.0 10,0 R412 555 .-, 10 ¢?, E o) E 1 v 0.1 0.01 1 400 R 555 •,-., lO ¢?, E E 1 0.1 R 2:0.847 0.01 1 10 R443 555 0.01 1 R51O sss Fig. 7. The relationship between -_sss,°4t;-=_ss,°a43,=5_5,40°and ,sssl°51°band ratios and chlorophyll concentrations less than 64mgm -3 (N --- 2,849, except for 4 _555 where N = 2,813). 16

Original page 23

O'Remyetal. 100 :/.2804 " .-" .'.,I- "INT:O.O00 " ." :* L,,('." "SLOPE: 1.000 ,..'; .,,,,,," , . R z" 0 883 ." ..'PL[._ " ".'" 10 ............ ,_ : v °. .... R :0.2 1 ",4. " ." "" ..-.;:£..- :" / ÷t/" .................................... ....-:,. :.,, 0.1 ..... :-,',', ;: ........ ............... 0.01 0.01 0.1 1 10 Ca (mg m-3) 64 32 0 -1.00 -0.75 -0.50 -0.25 O.OO 0.25 0.50 0.75 log(Ca ICa ) IO0 -,. . ;. ............ e) 10 E 1 o) %, ." E v t_ 0.1 0.01 O.OOl 0.1 1.0 10.0 4_ R5_ Fig. 8. Comparisons between OC2v4 modeled 100 i , ,),,), ) . .,,H,_ i i 1,1,,, . . ,i,, / . ¢o., // ........................t oo,/ .b)...t 100 0.01 0.1 1 10 100 Ca Quantiles (rag m-3) 1,0 ' ' ) i :;k ;::,,:....... '0.8 ._ o.6 LL _. o., i 0.2 c) 'd)d) 0.0 ] ]111 [ I I I I III _ I I IK_II ] _ 1.00 0.01 0,1 1 10 100 Ca (mg m-3) values (Ca) and in situ data (C=): a) Scatterplot of Ca versus Ca; b) Quantile-quantile plot of Ca versus Ca; c) Frequency distribution of log(Ca/Ca); d) Relative frequency of C (thin solid curve) and C=; e) Rss549° versus Ca. Also shown is the OC2v4 model (solid curve). 17

Original page 24

SeaWiFS Postlaunch Calibration 100 INT: 0.000 ': .-:.Et<.*'" SLOPE: 1.000 . ....: .- 10 RZ: 0.892 ,[.!,* .t',2"_ ,- .MS: 0.222 .: E • "" , t .+ 0.1 0.01 1 i iiiiii I I I #Ill and Validation Analyses, Part 3 ,,-, 1°° I ........................ OOl / ........ b) 0.01 • 0.1 1 10 100 o.ol Ol 1 lo lOO Ca(ragm-3) 340 N: 2804 306 MIN:-0.749 MAX: 0.742 MED: -0.010 272 MEAN: 0.000 STD: 0.222 238 SKEW: 0.295 KURT: 0.666 C ) 170 g138 ii 102 68 134 0 Ca Quantiles (mg m -3) ,o, ........ ,=^....................... f\h _ ,=..o. - o>"0.8 I %''= _ Ca LI. 0.6 i . 0.4 ID 0.2 O.OL /,, .,,..,td)d) ii1[ l I I Illl} I I I I LL_L -1.00 -o.75 -OiSO -0.25 0.00 0,25 0.50 0.75 1.00 0.01 0.1 1 10 lOO Iog(Ca/C a ) 100 10 E 1 E v 1(.3m 0,1 ++ 0.01 0.001 0.1 1.0 10.0 R544_ > R49°555>R_5 Ca (mg m-3) Fig. 9. Comparisons between OC4v4 modeled values (Ca) and in situ data (Ca): a) Scatterplot of Ca versus Ca; b) Quantile-quantile plot of Ca versus Ca; c) Frequency distribution of log(Ca/Ca); d) Relative frequency of Ca (thin solid curve) and Ca; e) =_49°=sssversus Ca. Also shown is the OC4v4 model (solid curve). 18

Original page 25

O'Reilly et al. value between Ca and (model) Ca is slightly higher with OC4 (0.892) than OC2 (0.883). Both models yield a relative frequency distribution that is approximately congruent with the Ca distribution. The OC2 and OC4 models are extrapolated to a Ca value of 0.001, well below the lowest concentration (0.008 mgm -_) present in the in situ data (Figs. 8e and 9e). If clear (clearest) water is operationally defined as Ca = 0.001mgm -3, then the clear water reflectance ratio /_443_k _ _555 ) predicted by OC4 is within the theoretical range given in Table 6, whereas the extrapolated clear water _490•_555 reflectance ratio for OC2 is greater than the theoretical clear water estimates. Because the OC2v4 and OC4v4 algorithms were tuned to the same data set, their Ca estimates should be very highly correlated and internally consistent, with a slope of 1 and an intercept of 0. This is illustrated in Fig. 10. The reduced scatter (orthogonal to the 1:1 line), centered at about 1 mgm -3, indicates the region where both algorithms use the 490 nm band. Additional noteworthy characteristics of OC4 are illustrated in Figs. 11 and 12. The .D443¢555ratio dominates (50%) at MBRs above approximately 2.2, D490• _555 between 2.2 and 1.1, and _510"_555 at MBRs below 1.1 (Fig. 11). With respect to chlorophyll concentration, the ,_443_555ratio dominates (50%) when Ca is below approximately 0.33 mg m -3, _49o"_555 for Ca between 0.33-1.4 mgm -3, and _51o_555 when Ca exceeds approximately 1.4 mg m -3 (Fig. 12). Relative to OC2v2, OC2v4 predicts slightly higher Ca above concentrations of 3 mgm -3 (Fig. 13), while OC4v4 generates slightly lower Ca estimates at very high concentrations (Fig. 14). At Ca below 0.03 mg m -a, OC2v4 estimates are very similar to OC2v2, while OC4v4 estimates the Rrs(A) data to compensate for wavelength differences among the sensors (Table 4). 2.4 CONCLUSIONS A large data set of/_rs and (_a measurements was compiled and used to update the OC2 and OC4 bio-optical chlorophyll a algorithms. The present data set, which is substantially larger (N=2,853) than that used to develop the version 2 algorithms (N=1,174), includes samples from a greater variety of bio-optical provinces, and better represents oligotrophic and eutrophic waters. Over the four-decade range in chlorophyll a concentration encompassed in the data set (0.008-90 mg m-3), the R490555 band ratio is the best overall single band ratio index of chlorophyll a concentration. In oligotrophic waters, however, the _443_555 ratio yields the best correlation with Ca and lowest RMS error, while in waters with chlorophyll concentrations exceeding approximately 3 mg m -3, the ps10"_555 ratio is the best-correlated index. OC4 takes advantage of this band-related shift in precision, and the well-known shift of the maximum of Rrs(A) spectra towards higher wavelengths with increasing Ca. Dispersion between the OC2 model and Ca tended to increase with increasing chlorophyll concentrations above 1 mgm -3, whereas dispersion using OC4 remained relatively low and uniform throughout the range of in situ data. Consequently, OC4 yields a slightly higher R 2 and lower RMS error than OC2. Statistical comparisons of algorithm performance with respect to in situ data, however, provide only partial information about their performance when applied to satellitederived water-leaving radiances. Operationally, OC4 would be expected to generate more accurate Ca estimates than are slightly higher than those from OC4v2, particularly so OC2 for several reasons. In oligotrophic water, OC4 would when Ca is below 0.01 mg m -3. (Version 3 equations were preliminary and provided to the SeaWiFS Project for testing and evaluation and are not described here.) There is considerable interest and benefit from comparing and merging data from various ocean color sensors (Gregg and Woodward 1998). This is one of the major objectives of SIMBIOS (McClain and Fargion 1999). In the particular case of ocean color data merging, one methodological issue to be resolved is how data from satellite sensors having different center band wavelengths can be merged to generate seamless maps of chlorophyll a distribution. Among several possible approaches, one is to develop internally consistent, sensor-specific variations of empirical chlorophyll a algorithms tuned to the same data set. This implies a comprehensive suite of in situ measurements at wavelengths matching the various satellite spectrometers or perhaps hyperspectral in situ data. To facilitate comparisons with SeaWiFS chlorophyll a, MBR algorithms for several ocean color sensors are presented in Table 7. These algorithms must be considered as an approximation, because the in situ data set is biased to SeaWiFS channels be expected to provide more accurate Ca estimates than OC2, because the signal-to-noise ratio (SNR) is greater in the 443 nm band than the 490 nm band. In eutrophic waters, strong absorption in the blue region of the spectrum results in lower SNR for water-leaving radiances retrieved in the 412nm and 443nm bands relative to the 490rim and 510nm bands. Furthermore, the influence of the atmospheric correction scheme on the accuracy of derived water-leaving radiances used in band-ratio algorithms must be considered. The SeaWiFS atmospheric correction algorithm (Gordon and Wang 1994 and Wang 2000) uses the near infrared bands (765 and 865nm) to characterize aerosol optical properties and estimates aerosol contribution to total radiance in the visible spectrum by extrapolation. The 510 nm band, being closer to the near infrared bands, is less prone to extrapolation errors than the 490 nm and 443 nm bands. In chlorophyll-rich water, therefore, OC4 would be expected to provide more accurate estimates of Ca than OC2. The present version of the/_rs(A) and Ca data set represents a significant improvement in size, quality, and bioand a number of radiometric adjustments were made to optical diversity when compared with earlier versions, but 19

Original page 26

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 Table 5. Regressionstatistics(reducedmajoraxis)for the linearrelationshipbetweenlog(measuredRrs) and log interpolated Rrs), where m is the slope and b is the intercept. Rr8 N R 2 510 853 0.995 520 350 0.990 531 770 0.995 550 258 0.999 555 914 0.998 560 197 0.998 565 350 0.989 m b 0.9948 0.00299 1.0328 0.06280 0.9614 -0.1005 0.9827 -0.0425 1.0032 0.01141 1.0178 0.02361 1.0487 0.11512 Table 6. Comparison between theoretical and extrapolated clear water reflectance ratios using OC2 and OC4 algorithms, where a is the absorption per meter, bb is the backward scattering coefficient per meter, and f is the function (unspecified). The theoretical reflectance ratios are based on the absorption and backscattering values from Pope and Fry (1997) and Morel (1974). R,s Band Ratio Rrs = fa+b_bh-- 443:555 16.53 490:555 6.13 Rr_ = ] _ Algorithm 21.78 18.21 (OC4) 6.66 7.502 (OC2) Table 7. The maximum band ratio algorithms for the SeaWiFS, CZCS, OCTS, MODIS, and MERIS sensors. As with the OC4, OC40, and OC4E algorithms, the argument of the logarithms for OC3M and OC3C is a shorthand representation-for-t-he maximum of the indica_e(l values. Sensor Name Equation SeaWiFS OC4 Ca -- 10.0 (0.366 - 3.067R4s + 1.930R_s + 0.649R3s - 1.532R_s) [D443 D490 D510_ where R4s = logl0 _,L555 > -_555 > -5551 MODIS OC3M Ca = 10.0 (0.2830 - 2.753R3M + 1.457R_M + 0.659RIM -- 1.403R_M) [D443 D490 where R3M ---- lOgl0 V_55o. > "5501 OCTS OC40 Ca = 10.0 (0.405 - 2.900R4o + 1.690R20 + 0.530R30 - 1-144R4o) [D443 490 D520 where R4o : log10 _-_565 > R565 > -_5651 CZCS OC3C Ca = 10.0 (0.362 - 4.066R3c + 5.125R2c - 2.645R33c - 0.597R_c) [D443 ]520 where R3c : log10 vL550 > -550! MERIS OC4E Ca = 10.0 (0.368 - 2.814R4E + 1.456R_E + 0.768R_s - 1.292R_E ) [D443 D490 DS10 where R4E = lOglo _-_56o > ,_560 > -_s60! 2O

Original page 27

O'ReiUyet al. : 0.992 000R BIAS:0.000 RMS: 0.058 10.00 1.00 0.10 +. + + -1.,-I- 0.01 • J t llLl 0+01 0.10 OC2v4 (mg m "3) , 1 , i le,,, + + +=" . , i = ixll J = , i,, 1.00 10.00 100.00 Fig. 10. Comparisons of Ca from OC2 and OC4 when using ]r8 from the in situ data set. 100 90 80 o-e 70 O 60 o" 50 40 I1) 30 , ! 20 J i/ i : 10 0 1 443 > 490 ,,..510 R555 ......i - ........i ..................... ........--:;,, J, _3 .......... !! s55 , : .... R490 E 555 ! i i -..,R510 i s55 i i i i ......... T'"--, ?: 10 R555 r.. 555 Fig. 11. The relative frequency of band ratios used in the OC4 model versus the maximum band ratio. 21

Original page 28

SeaWiFS Postlaunch Calibrationand Validation Analyses,Part 3 100 .......:;=';". 0 ....... {....4 0.10 Ca (mg m -3) t l]i LLL , r: Jii I':I 1 ] lil Ii1 ,! -!.......-4,,J-+_ 4_ ..... 10.00 100.O0 Fig. 12. The relative frequency of band ratios used in the OC4 model versus chlorophyll concentration. 100 ..................................."_ii-__--__oc2v2: 10 E 1 E rO 0.1 0.01 ...................................................... | | 0.001 | r I I I i I I I J _ _ _ _ _ _|' 0.1 1.0 10.0 490 R555 Fig. 13. The comparison of Ca estimates from OC2v4 with OC2v2. 22

Original page 29

O'Reillyet al. IO0 i...... -, 0C4v2 ...... I0 i ........... ::::, =.0C_v4 cO ! E 1 E V 0.1 0.01 0.001 1 : , ] • ...... "'" "" " ""-: _ ""T ................................ 10 R443 >R4_90 >R510 555 Fig. 14. The comparison of Ca estimates 555 555 from OC4v4 and OC4v2 models. it still lacks observations from the clearest oceanic waters. tion of the global ocean, these and highly eutrophic areas These observations are required to resolve the asymptotic represent bio-optical and ecological extremes and changes relationship expected between Rrs()) and Ca as chloro- in their magnitude or areal distribution may provide very phyll a concentration diminishes below 0.01 mgm -3, and sensitive indicators of global change. reflectance band ratios approach the theoretical values for pure sea water. They are also needed to determine if the OC2 and OC4 extrapolations beyond the lowest C'_ are accurate. Given the spatially and temporally comprehensive The authors would like to acknowledge the following individuals time series achieved by the SeaWiFS mission, these clearfor their significant contribution of in situ data and ideas: J. ACKNOWLEDGMENTS est water regions and optimal sampling times may now be Marra, C Davis, D. Clark, G. Zibordi, C. Trees, R. Bidigare, easily identified and targeted for special shipboard surveys. D. Karl, J. Patch, R. Varela, J. Akl, C. Hu, A. Subramaniam, Although clearest waters encompass a relatively small frac- N. Nelson, T. Michaels, R. Smith, and A. Morel. 23

Original page 30

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 Chapter 3 SeaWiFS Algorithm for the Diffuse Attenuation Coetticient, K(490), Radiances at Using Water-Leaving 490 and 555 nm JAMES L. MUELLER CHORS/San Diego State University San Diego, California ABSTRACT A new algorithm has been developed using the ratio of water-leaving radiances at 490 and 555 nm to estimate K(490), the diffuse attenuation coefficient of seawater at 490 nm. The standard uncertainty of prediction for the new algorithm is statistically identical to that of the SeaWiFS prelaunch K(490) algorithm, which uses the ratio of water-leaving radiances at 443 and 490 nm. The new algorithm should be used whenever the uncertainty of the SeaWiFS determination of water-leaving radiance 3.1 INTRODUCTION The attenuation over depth z (in meters), of the spectral downwelling irradiance, Ed(A, z) (in units of mW cm -2 nm -1 at wavelength A), is governed by the Beer-Lambert Law: at 443 is larger than that at 490 nm. A and B are coefficients derived from linear regression analysis of the data expressed as In[K(490) - K_(490)] and ln[Lw(Al)/Lw(A2)]. In Austin and Petzold (1981), Kw(490) = 0.022m -1 was taken from Smith and Baker (1981), and because the algorithm was derived for CZCS, A1 = 443nm and X2 = 550nm. Ed(A, z) = Ea(A,0-) e -K('z)z, (6) The SeaWiFS ocean color instrument has channels at per 443 and 555 nm. Mueller and Trees (1997) found a difwhere K(A, z) is the diffuse attenuation coefficient in be- ferent set of coefficients for (8) using wavelengths )h = unit meters, averaged over the depth range from just Gor- 443 nm and )2 - 555 nm, and also used the ratio of norneath the sea surface (z = 0-) to depth z in meters. remotely malized water-leaving radiances. The substitution of nordon and McCluney (1975) showed that 90% of the upper malized water-leaving radiances in (8) had no significant sensed ocean color radiance is reflected from the layer, of depth Z9o, corresponding to the first irradiance attenuation length, thus satisfying the condition (7) assumed K(490) = 0.022m -1 (Smith and Baker 1981). Ed( ,zgo) = e_l. Ed( ), O-) The depth zg0 is found from an irradiance profile, by inspection, as the depth where condition (7) is satisfied. effect, but the change in )_2 yielded small, but statistically significant different coefficients A and B. Following Austin and Petzold (1981), Mueller and Trees (1997) also The Mueller and Trees (1997) result was adopted for the SeaWiFS prelaunch K(490) algorithm. SeaWiFS determinations of Lw(443) are persistently lower than water-leaving radiances that are determined From (6), the remote sensing diffuse attenuation coefficient from matched in situ validation measurements. The seriat wavelength A can be found as K(A) = Zgo1 m -1. ous underestimates of SeaWiFS Lw (443) yield correspond- Austin and Petzold (1981) applied simple linear regres- ingly poor agreement between SeaWiFS and in situ K(490) sion to a sample of spectral irradiance and radiance profiles determinations. On the other hand, SeaWiFS determinato derive a K(490) algorithm of the form (8) (8) using 490 and 555nm, which should yield improved K(490) = Kw(490) + A[L---W-_2)] , for also adopts a reduced value of K_o(490) based on recently where Kw(490) is the diffuse attenuation coefficient tions of Lw(490) and Lw(555) agree much more closely with validation measurements. This chapter is the report of an algorithm based on uncertainty in SeaWiFS K(490) estimates. The algorithm pure water, Lw()u) and Lw(A2) are "water-leaving radi- published values of pure water absorption (Pope and Fry ances at the respective wavelengths of _1 and t2, and 1997). 24

Original page 31

O'Reillyet al. 3.2 DATA AND METHODS Two samples of K(490) and normalized water-leaving radiances are used in the present analysis. Sample 1 is used for a regression analysis to derive coefficients A and B for (8) with )1 = 490nm and ),2 = 555nm. The data in Sample 2 are entirely independent from Sample 1 and are used to determine standard uncertainties of prediction in K(490) calculated using the algorithm derived here from Sample 1, and using the prelaunch K(490) algorithm (Mueller and Trees 1997). The data comprising Sample 1 were drawn from spectral irradiance and radiance profiles locally archived at the San Diego State University (SDSU) Center for Hydro- Optics and Remote Sensing (CHORS). Each Sample 1 profile was analyzed to determine K(490) and water-leaving radiance using the integral method of Mueller (1995a). Sample 1 includes the data analyzed by Mueller and Trees (1997), but excludes two cruises for which reliable upwelled spectral radiance profile [L_(490, z)] measurements were not available. Data from two additional cruises in the Gulf of California were added to Sample 1, bringing the total sample size to 319 data pairs. Sample 2 was provided from the SeaBASS archives by the SIMBIOS Project Office at GSFC, and consists of 293 sets of K(490), water-leaving radiances and incident surface irradiances (443, 490, and 555 nm) which are indepen- 1 this subsample of 31 pairs). The mean biases in predicdent of Sample 1. Water-leaving radiances in Sample were determined by the SIMBIOS Project using the standard methods employed at GSFC for SeaWiFS match-up validation analysis. K(490) and normalized water-leaving radiance ratio pairs were determined for each sample using the methods described in Mueller and Trees (1997). A linear regression analysis was performed on the Sample 1 data pairs to determine the values of coefficients A and B in (8), with ),1 = 490nm and )2 = 555nm. Based on Pope and Fry's (1997) recent determination of absorption for pure water aw(490) = 0.015 m -1, and the pure water backscattering coefficient bw(490) = 0.008m -1 reported by Smith and Baker (1981), the backscattering fraction is heuristically assumed to be less than 0.5 and performed three regressions assuming values of 0.018, 0.017, and 0.016 m -1 for K_ (490). Finally, standard uncertainties of prediction were calculated, both for the present (490 and 555 nm) and the prelaunch (443 and 555nm) algorithms, as the RMS in much lower than those for LWN (443). It is recommended, differences between the measured and predicted K(490) Sample 2. 3.3 RESULTS Three regression analyses were performed on Sample 1 using successive values of 0.018, 0.017, and 0.016m -1 for Kw(490). The scatter between In[K(490) - 0.016] and in lating a regression equation beyond the range of the data ln[Lw(a90)/Lw(555)], in per unit meters is illustrated Fig. 15a, together with the logarithmic regression line corresponding to the algorithm r LwN (490) 1 - 1.5401 (49o) = 0.016+ 01 645[ ] (9) In log space, the squared correlation coefficient R 2 increased monotonically from 0.931-0.937, and the standard error decreased from 0.186-0.167, as Kw(490) decreased from 0.018-0.(}16m -1. On this basis, the appropriate algorithm selected for use with SeaWiFS was the Kw(490) = 0.016m -l case. In linear space, the standard uncertainty of the estimate, calculated as the RMS discrepancy between predicted and measured K(490) for Sample 1, is 0.012 m -1. The scatter between predicted and measured K(490), relative to the one-to-one line, is illustrated in Fig. 15b. Figures 16a and 16b illustrate the scatter about the one-to-one line when K(490) predictions using (9) are compared to measurements from Sample 2. The standard uncertainty of prediction in K(490) using (9) is estimated from these data to be 0.018m -l in the range of K(490) < 0.25m -1 (which is the range fit with Sample 1) and corresponds to 26% of the mean for this subsample of 249 pairs. When the algorithm of (9) is extrapolated into the range K(490) > 0.25 m -1, the standard uncertainty of prediction increases to 0.193 m -1 (48% of the mean for tions are -0.002m -1 for measured K(490) <0.25m -1, and -0.130m -1 for measured K(490) > 0.25m -1. The standard uncertainties and mean biases of prediction for K(490) calculated with the SeaWiFS prelaunch algorithm (Mueller and Trees 1997) are 0.020 and 0.000 m -1, respectively, for the subsample of Sample 2 with measured K(490) <0.25 -1, and 0.196 and -0.085m -1 for the subsample with measured K(490) > 0.25 m -1. 3.4 DISCUSSION There is little to choose between the in situ performances and uncertainties of the (9) K(490) algorithm, using the ratio of water-leaving radiances at 490 and 555 nm, and the SeaWiFS prelaunch algorithm (Mueller and Trees 1997), using the ratio of water-leaving radiances at 443 and 555 nm. When used with SeaWiFS data, however, (9) may be expected to yield more accurate K(490) estimates as long as the uncertainties in estimated LWN(490) are therefore, that (9) be substituted for the Mueller and Trees (1997) K(490) algorithm for processing SeaWiFS data, at least until future improvements in atmospheric corrections may produce equivalent uncertainties in water-leaving radiances at 490 and 443 nm. Neither algorithm performs well in water masses where K(490) >0.25m -1. In part, this may be due to extrapo- 25

Original page 32

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 0"5"• a J _D -0.5 _ ® _'-1.5- '-2.5' " -3,5, t-. -4.5- -5.5- 0.30- 0.25- ! ' 0.20- _" 0.15- 0.10- Q- 0.05- 0.00- -0.5 0.0 0.5 1.0 1.5 2.0 2.5 0.00 0.05 0.10 0.15 0.20 0.25 0.30 In[LwN(490)ILwN(555)] Measured K(490) [m -1] Fig. 15. Scatter comparisons of K(490). a) Logarithmic scatter comparison of K(490) versus the ratio of water-leaving radiances at 490 and 555 nm. The solid line is the least squares regression fit to the data (excluding the GoCa198A red tide data) given by (9). b) Linear scatter in measured K(490) compared with predictions using (9) with the ratio of water-leaving a). The key for these panels are: 1. Siegel: Sargasso radiances at 490 and 555 nm. The data are from panel Sea 1994; 2. Mitchell: CalCOFI 1994; 3. GoCal 1995; 4. GoCal 1997; 5. CoCal !998A (with Red Tide Station); 6. GoCal 1998A Red Tide Data; 7. Trees, Arabian Sea, JGOFS Proc. 2; 8. Trees, Arabian Sea, JGOFS 1.0al .e. o O.6o) ® "o _® ® m 0.4- 8D .-_o "o 2 i(® ® 0..- 0.2- " oo i Proc. 6; 9. Trees, Arabian Sea, JGOFS Proc. 7. 0.30bl 0.25v & ...... 0.20o o') ® ® " 0.15 _ ® "a m 5 " 0.10- Q- 0.05. 0.00olo 0.2 0.4 0.6 0.8 i.0 0.oo 0.05 0.10 0.15 020 0.25 0.30 MeasuredK(490)[m -1] MeasuredK(490) [m "1] Fig. 16. Scatter comparisons of K(490). a) Same as Fig. 15b, but for an independent sample of K(490) and water-leaving radiances at 490 and 555 nm. The solid line corresponds to a one-to-one agreement, b) A subset of panel a), where the area of greatest concentration of data points is enlarged for better viewing. The key for these panels are: 1. BATS 1998; 2-5. CalCOFI-9802, -9804, -9807, and -9809, respectively; 6. April 1998 SMAB; 7. November 1998 SMAB; 8. Feb 1999 SMAB; 9. CARIACO 1998; 10. GoA97; and C) HOTS 1998. 26

Original page 33

O'Reillyet al. usedto fit its coefficients.In the presentcircumstances,termination, and uncertainty in extrapolating L_(£, z) to however,it is at leastequallylikelythat the poorpre- the sea surface (especially when the linear slope estimadictionsresultfromextremelylargeuncertaintiesin both tion method of analysis is employed) contribute large and K(490) and water-leaving radiances derived from radio- poorly understood uncertainties to measured K(490) and metric measurements near the sea surface in extremely water-leaving radiances alike. For the near term, the best turbid water masses. In such cases, instrument self shad- policy is to regard SeaWiFS K(490) data with values of ing, wave focusing, uncertainty in instrument depth de- greater than0.25 m -1 with caution and skepticism. 27

Original page 34

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 Chapter 4 Long-Term Calibration History of Several Marine Environmental Radiometers (MERs) MARGARET C. O'BRIEN, DAVID W. MENZIES, DAVID A. SIEGEL, AND RAYMOND C. SMITH ICESS, University of California, Santa Barbara Santa Barbara, California ABSTRACT The accuracy of upper ocean AOPs for the vicarious accurate and consistent in situ radi0metric data. calibration of ocean color satellites ultimately depends on The SIMBIOS Project is charged with providing estimates of normalized water-leaving radiance for the SeaWiFS instrument to within 5%. This, in turn, demands that the radiometric stability of in situ instruments be within 1% with an absolute accuracy of 3%. This chapter reports on the analysis and reconciliation of the laboratory calibration history for several BSI MERs, models MER-2040 and -2041, three of which participate in the SeaWiFS Calibration and Validation Program. This analysis includes data using four different FEL calibration lamps, as well as calibrations performed at three SIRREXs. Barring a few spectral detectors with known deteriorating responses, the radiometers used by UCSB during the BBOP have been remarkably stable during more than five years of intense data collection. Coefficients of variation for long-term averages of calibration slopes, for most detectors in the profiling instrument, were less than 1%. Long-term averages can be applied to most channels, with deviations only after major instrument upgrades. The methods used here to examine stability accommodate the addition of new calibration data as they become available; this enables researchers to closely track any changes in the performance of these instruments and to adjust the calibration coefficients accordingly. This analysis may serve as a template for radiometer histories which will be cataloged by the SIMBIOS Project. 4.1 INTRODUCTION in the Santa Barbara Channel, and the Palmer Area Long Term Ecological Research (LTER) site on the Antarctic The accuracy of upper ocean AOPs, which are needed Peninsula. The ICESS Calibration Laboratory and BBOP - for the vicarious calibration of ocean color satellites, ultihave participated in all of the workshops held by the Calmately depends on accurate and consistent in situ radio- ibration and Validation Program. metric datal Accurate validation of SeaWiFS demands in-water radiometric stability within 1%, with an accuracy an This report presents an analysis of the multiyear laboratory calibration history for several BSI MERs, models - of 3% (Mueller and Austin 1995). Considerable energy MER-2040 and -2041. This analysis includes data using : has been spent refining calibration protocols for profiling four different FEL calibration lamps, as well as calibra- - radiometers. The SeaWiFS Project Office has sponsored tions performed at three SIRREX exercises. This report several workshops through its Calibration and Validation will show that, barring a few sensors with known deteri- --- Program, which have yielded significant improvements in orating responses, the radiometers used by UCSB during the research community's ability to provide accurate AOP BBOP have been remarkably stable during six years of estimates. These include the SIRREXs, conducted annu- intense data collection. ally since 1992 (Mueller 1993, Mueller et al. 1994, Mueiler et al. 1996, and Johnson et al. 1996), as well as the Data 4.2 ICESS FACILITY AND METHODS Analysis Round-Robin (DARR) workshop in 1994 (Siegel et al. 1995). Sci- climate-controlled room. A 1.2 x 1.8 m (4x 6 ft) optical ta- At the Institute for Computational Earth System provide ble, with threaded holes arranged in a 2.5 cm (1 in) grid, ence (ICESS) at UCSB, several research projects The ICESS optical calibration facility is housed in a validation data for ocean color satellites. These include supports one end of a 2.4 m (8 ft)|ong Optical rail. h black, Project wooden baffle with a 25.4cm (10 in) diameter hole strad- BBOP in the Sargasso Sea, the Plumes and Blooms 28

Original page 35

O'Reillyet al. dlestherail61.0cm(2ft) fromtheilluminationendofthe lamp holder's vernier stage is used to make the final disof tance adjustment. benchandextendsthefull 1.2m(4ft) widthby aheight 1.5m (5ft). A 30.5cm(12in) squareplatecanbebolted Beginning in July 1992, radiance calibrations were periris formed using a 50.8cm (20in) diameter Labsphere, Inc., overthe baffleholeto holda 7.6cm(3in) adjustable of a helium- integrating sphere with a variable (2.54-10cm, 1-4in diif necessary.An alignmentbeam,consisting neon(He:Ne)laserwithtwoadjustablemirrors,iscenteredameter) entrance aperture and 15.2 cm (6 in) diameter exit ona plat- aperture located 90 ° from the entrance. It is illuminated onthe hole,parallelto the rail,andis mounted format the distalendof the opticalrail. Thetableand externally by the same FEL lamp used for irradiance calcurtain ibrations. The sphere is positioned on the bench at the rail assemblyaresurroundedby a black,pleated ontheceiling.Whenthe end of the optical rail and the lamp is positioned 50 cm suspendedfroma trackmounted roomlightsareoffandthecurtainsdrawn,nodetectablefrom the sphere's 5 cm (2 in) diameter entrance aperture. in the The raised platform with the scissor jack is positioned to lightreachestheinstrumentexceptthroughthehole baffle.Shadowformscanbeinsertedbetweenthelamp and instrument to block direct light during the measurement of stray light. The lamp holder array consists of a sliding platform on the optical rail supporting two horizontal vernier stages at right angles, a rotary stage, a vertically adjustable post, and an FEL lamp holder. An alignment jig replaces the lamp in the holder to properly position the lamp holder to the alignment laser beam. The lamp holder array can be easily slid along the rail to provide calibration distances from 50 cm to over 2 m. The standard lamps are purchased from, and calibrated by, Optronic Laboratories, Inc3 (Orlando, Florida) and calibrations are traceable to the National Institute of Standards and Technology (NIST). An 83-DS power supply with a 0.02 f_ shunt provides power for the FEL lamp. A 4.5 digit voltmeter is used to monitor the current and voltage during calibrations. The lamp is allowed to warm up for 10 min before each calibration. The current is maintained at 8A (=i=l mA) and is reproducible to 0.03%. hold the test instrument a few centimeters from the exit aperture and the wooden baffle; black felt is used to block all stray light. Beginning in August 1994, radiance calibrations were also performed using a 60.1cm (24in) Spectralon(_ reflectance plaque. At the extreme end of the optical bench, a vertical bracket at the plaque's center supports it at a position normal to the laser alignment beam. The lamp holder is positioned at a distance of 200 cm from the plaque, and a baffle with a 25.4 cm (10 in) diameter hole between the lamp and the plaque allows the lamp to illuminate only the plaque. The scissor jack and its platform are moved to align the radiance collector at 45 ° to, and 33 cm (13 in) from, the plaque. From 1994-1996, radiance calibrations were performed routinely using both the sphere and the plaque. 4.2.1 Calibration Lamp History Three NIST-traceable FEL lamps were used for calibrating the ICESS radiometers--F219, F303, and F304-- The mounting platform for radiometers consists of a all of which were purchased from Optronic Laboratories. large scissor jack, which can support instruments up to 22.7kg (501bs.) and 20.3cm (8in) in diameter. The jack has independent height and crossbeam adjustments to cen- There are manufacturer's calibrations for all three lamps. At UCSB, lamp F219 was used for all calibrations from 1989-1991 (Fig. 17). Since that time, it has been used only ter the instrument on the optical axis. It is attached to a during lamp intercalibration experiments, so there should 45.7 cm (18 in), square platform which in turn, can be fastened to the optical bench at any location with 15.2cm (6 in) tall aluminum posts which are 43.2cm (17 in) apart. Because the hypotenuse of a 30.5 cm (12 in) right triangle is 43.1cm (17in), the platform can be easily positioned have been no further significant aging of this lamp. Lamp F303 was purchased in June 1992 and was used for all routine calibrations at UCSB from July 1992-July 1995. Lamp F303 was recalibrated by Optronic Laboratories in July 1995 after approximately 50 h of service. Lamp F304 at the 45 ° angle desired for radiance calibrations with a was a seasoned, uncalibrated FEL lamp, purchased in June reflective plaque. 1992, and used only a few hours until July 1995 when it was During irradiance calibrations, the test instrument is calibrated by Optronic Laboratories and put into use for positioned so that its cosine collector is centered on the alignment beam and normal to it. Calibrations are usually performed at a distance of 50 cm, which is measured through the baffle iris using a 50 cm measuring rod. The [ Certain commercial equipment, instruments, or materials are identified in this technical memorandum to foster understanding. Such identification does not imply recommendation or endorsement by NASA, NIST, or ICESS, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. routine calibrations at UCSB. A fourth lamp, F305, was not calibrated by the manufacturer, but has been used for comparisons between other lamps. All four lamps were intercalibrated during at least two of the three SIRREX calibration workshops in July 1992, June 1993, and September 1994. F219 was examined at SIRREX-1 and again at SIRREX-2 in June 1993. Lamp :_ Spectralon is a registered trademark of Labsphere, Inc., in North Sutton, New Hampshire. 29

Original page 36

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 ,°°°°.°°.°°°° ..... ®F219 1989 °,.°°°°°°,° 1990 1991 ®F303 1992 ,..,°.,° 0 SIRREX ® Lamp Calibrations at Optronics 41, xfer cals vs day of exp O F219, F303 ....... ° ............ ° ° , _ F219, F303, F304, F305 O 1993 1994 oF303, F304 1995 ® O 1996 1997 F304, F305 ,I, F304 to F219, F303, F305 F303, F304 F304to F303, F305 Fig. 17. A timeline of FEL lamp calibrations at Optronic Laboratories, transfer calibrations at UCSB, and SIRREX experiments. 30

Original page 37

O'Reillyet al. Table 8. Wavelengthcentersandbandwidthsmeasuredat full-widthat half-maximum(FWHM)power(in parentheses).All valuesarein nanometersandthe upwelledspectralradianceis denotedas E_,(z,£). The channels marked with [_ were added in 1994. If a detector has been replaced, the wavelength given is the one most recently measured. The column headings denote type. 2040 S/N 8728 2041 S/N 8729 Ed(O+, Ed(0+, X) FWHM Center FWHM Center FWHM Center FWHM [nm] Center FWHM Center FWHM Center 340 380 410 410.2 9.6 411.2 9.4 410.4 441 441.6 10.8 441.7 10.7 441.7 465 465.4 10.0 465.8 9.7 488 488.0 9.9 486.7 9.6 487.8 510 510.2 [-_ 9.3 511.9 I-_ 8.2 520 518.6 11.5 519.4 11.4 519.5 540 555 555.2 I-_ 9.8 555.7 _ 9.8 565 564.8 11.1 565.5 10.9 564.6 587 587.1 10.4 586.0 9.9 625 623.4 [_] 10.7 624.8 [J 10.7 665 664.4 9.5 664.8 9.4 662.9 683 680.3 [ 9.0 681.1 10.0 F303, which has been used extensively for calibrations at UCSB, was examined at all three SIRREXs; F304 and F305 were both tested at SIRREX-2 and -3. In addition, a BSI Profiling Reflectance Radiometer (PRR) with the same type of photodiodes as the MERs, which was calibrated with lamp F303, was used for one of the training sessions at SIRREX-4 at NIST in May 1995. In addition to the SIRREX comparisons, one other comparison between lamps was performed at UCSB. Before F304 replaced F303 as the lamp used for routine calthe MER model and serial number, and the collector 2041 SIN 8734 2040 S/N 8714 340.3 8.4 378.4 10.0 9.5 410.4 10.4 410.3 11.4 410.8 11.4 10.9 442.2 10.4 441.5 11.1 442.0 12.1 464.0 9.5 10.1 488.5 11.4 483.6 10.7 487.9 10.8 507.4 11.1 507.5 11.4 10.3 518.5 10.0 520.1 8.5 518.0 8.3 537.8 9.5 11.7 563.4 10.8 563.4 10.8 563.3 9.5 585.4 10.2 587.0 9.6 586.5 10.5 622.6 10.6 624.0 12.1 624.2 12.0 11.2 663.0 9.7 662.4 9.3 680.8 13.9 mounted in a Gershun tube array. The half-angle field of view is 10.2 ° in air and 13.7 ° in water. Instrument 8714 is known as the Bio-Optical Profiling System II (BOPSII) and was described in Smith et al. (1997). Radiometers 8728 (MER-2040) and 8729/8734 (MER- 2041) are used routinely in the BBOP at the Bermuda Atlantic Time Series (BATS) station and have been calibrated three or four times per year since July 1992 (Table 8 and Fig. i8). The BBOP profiling instrument (S/N 8728) was designed originally with eight downwelling iribrations, the 1995 Optronic Laboratories calibration for radiance channels (410-665 nm) and nine upwelling radilamp F304 was transferred onto F303, F219, and F305 ance channels (410-683 nm). In January 1994, it was modusing a third MER-2040 instrument (S/N 8733) with 13 ified to meet the SeaWiFS protocols (Mueller and Austin irradiance channels between 340-683nm. As mentioned above, F219, F304, and F305 were used only during the SIRREXs and had not aged between 1992 and 1995. The transfer from F304 to F303 and F305 was repeated in May 1996. 4.2.2 Radiometers At the UCSB optical calibration facility, there are calibration histories for five BSI spectroradiometers [serial numbers (S/N) 8728, 8729, 8733, 8734, and 8714] spanning up to seven years (Fig. 18). The MER-2040 series of spectroradiometers is composed of discrete, sealed photoa ally on BBOP. It has been calibrated approximately once diodes, each with triple cavity interference filters giving nominal full-width at halbmaximum bandwidth of 10 nm. The wavelength centers range throughout the visible and ultraviolet-A (UVA) spectrum from 340-683 nm. The radiance detectors are identical 3-cavity filtered photodiodes 1995) and the number of channels was increased to 12 each of downwelling and upwelling channels (410-683 nm), plus upwelling natural fluorescence. The gains of all channels were also adjusted at this time. The original deck sensor (S/N 8729) has six downwelled channels (410-665 nm) and the optics have not been modified. In August 1994, it was replaced by S/N 8734, which has 13 downwelled channels (340-683 nm). Radiometer 8733 (MER-2040) was used intensively in the field from 199.2-1993 during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE) and is now used occasionper year. Instrument 8733 has 13 each of downwelled and upwelled irradiance channels between 340-683 nm. Radiometer 8714, the BOPSII (MER-2040), has been used for profiling on all of the Palmer Area LTER and Ice Colors 31

Original page 38

SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3 i ol,,,ololt g.lo.,o.o..,o, ............................................... ............................................... 1989 . "fi .......... I_tmment Calibrations I ......O BOPS: S/N8714 1990 OP: S/N8728 1991 o • i° ,.°°°°°o°°o,°°°o..°°° 1992 ° o _ _ _ .................0 _ O 1993 ° ............. i 0 _ Add detectors to 8728, 0 .................0 increase gain 1994 O O 1995 ....t ....................<> 1996 i 4_ ....!.............................O First Plaque Calibration Add detectors to 8714 o _ 8728: Ed(665), Lu(665) i, oo............%, t .............................O ..................O 8728: Ed(510), Lu(510) 1997 + O 8734: Ed(340) Fig. 18. A timeline of calibrations and upgrades for BBOP (S/N 8728, 8729, and 8734) and BOPSII (S/N 8714) radiometers. 32

Original page 39

O'Reilly et al. Table 9. Comparison of lamp irradiances between 400 and 700 nm obtained from SIRREX experiments, Optronics, and the transfer of lamp F304 to F305. The data values are the ratios of lamp output measured during the SIRREX experiments to those provided by Optronics is indicated by a. SIRREX- 1 Lamp Mean a F303-92 1.0087 0.0083 F303-95 0.9710 0.0104 F304-95 F305t F219-89 1.0332 0.0079 F219t 0.9854 0.0096 t Transfer calibration from F304. cruises in Antarctic waters, as well as many open ocean projects, and has been calibrated once or twice yearly since February 1989 (Fig. 18). This instrument had 8 channels of downwelled irradiance (increased to 13 for 410-665 nm in November 1994), and 8 channels of upwelled irradiance (410-624 nm, Table 9). Both 8728 and 8714 had individual detectors replaced. This report is primarily concerned with the BBOP instruments, because they contribute data to the SeaWiFS Calibration and Validation Program. Data from the BOP- SII and TOGA-COARE instruments (S/N 8714 and 8733) are used primarily to corroborate the conclusions, because their calibration histories are at least as long as that of the BBOP instrument and their calibrations involve the same lamps. The wavelength properties of each detector were measured using a double-grating monochrometer. An uncalibrated FEL lamp and condensing lens were used as the illumination source for the entrance slit, and the output spot was centered on the radiometer's cosine collector or on an individual radiance detector. The wavelength producing the maximum signal was determined, followed by or to the transfer calibration. The standard deviation SIRREX- 2 SIRREX- 3 Mean (7 Mean a 1.0178 0.0087 1.0332 0.0084 0.9788 0.0037 0.9932 0.0028 0.9916 0.0045 0.9919 0.0029 0.9895 0.0041 0.9905 0.0027 1.0414 0.0107 0.9937 0.0038 3) Long-term averages of calibration coefficients should be calculated whenever possible. 4.3.1 Lamps FEL lamp F303 was used continuously for all calibrations from 1992-1995 for a total of approximately 50 h. Optronic Laboratories specifies that lamp irradiances are accurate and stable to within approximately 1% for 50h or 1 year of use when the supplied current is maintained to within 0.1%. The two manufacturers' calibrations in 1992 and 1995 for F303 indicated that its output had changed by up to 5% and that it should not be used for further radiometer calibrations. The most extreme changes were noticed at wavelengths less than 500 nmt. Currently, F303 is used only for monitoring the performance of its replacement, F304. Given the possible change in the performance of the primary lamp, the response histories o_[ two radiometers were examined with both lamp calibrations for evidence supporting the validity of one or both calibrations. Because there is no long interruption between the calibrations of BBOP instruments (S/N 8728 and 8729/8734 the wavelengths on each side of the peak producing 50% of are calibrated every 3-4 months), the slopes of radiomethe maximum signal. The reported wavelength for a detector is the average of the two half-maximum wavelengths; its bandwidth is the difference between these two wavelengths (Table 8). The wavelength response of the monochrometer was calibrated by observing the visible spectral lines of a mercury pen lamp. Repeat determinations for any detector have agreed to within 0.5 nm. 4.3 RESULTS Because this report is concerned with accuracy, as well as radiometer stability, significant attention has been given to the calibrations of the lamps. The following discussion will illustrate: a) Calibration lamp output must be examined closely; 2) The two profiling instruments (BBOP S/N 8728, and BOPSII S/N 8714) appear to be stable over several years; and ter 8728, calibrated with lamp F303 between January 1994 and August 1995, were calculated using both the 1992 and 1995 Optronic Laboratories irradiance calibrations for this lamp. To compare the relative changes over time, each slope was normalized to that determined on 9 August 1995, the date on which lamp F304 replaced F303. The normalized slopes calculated with both lamp calibrations were examined for drift or step changes, which might indicate when the calibration lamp's output had changed. While using a single FEL lamp and calibration, most channels on the BBOP profiling radiometer (S/N 8728) showed a constant calibration response over time (Fig. 19). When a different FEL lamp or a different calibration of the same lamp was used, however, there were significant changes of t The raw data are available at the following universal resource locator (URL) address http://w_n_, icess, ucsb. edu/bbop. 33

Original page 40

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 F303 F304 1992 1995 1995 Ea(410) @ O • 1.08 Ed(488) IZl [] • Ed(565) • ix • o .,,4 o 1.06 Ea(683) ® 0 • o (.9 1.04 ® . 1.02 ® ® i 0.981.00 0 Z 0.96 ' ' J ' ' I , 1992 1993 1994 Fig. 19. The normalized calibration coefficients ® ® • [] ® [] • _) • ® o norm i I i i I , i l i 1995 1996 1997 1998 Year for four downwelling irradiance channels (radiometer 8728) using Optronic Laboratories calibrations of lamp F303 in 1992 and 1995. Data were normalized to the F304 values measured on 9 August 1995, the first date for which lamp F304 was used 2-6% in the coefficients for most of the channels. Agreement was best between lamps or calibrations employing the July 1995 Optronic Laboratories calibration for lamps when ratories apparently was not possible. It was implausible F303 and F304. In fact, the agreement was excellent for that the responses of two different radiometers had drifted the 1995 Optronic Laboratories calibration was used 1992 with the same rate and magnitude as did the output of all radiometer calibrations with lamp F303 back to (below). The response of the BOPSII radiometer (S/N 8714) to new lamps, or different calibrations of a lamp, was similar ferent lamp irradiances led to a more in-depth analysis of the lamp calibrations. Simply computing coefficients using the current lamp irradiances provided by Optronic Labolamp F303. 4.3.2 SIRREX Data to that of radiometer 8728. There were marked steps in The data from the three SIRREX activities were examthe slopes for each irradiance channel when lamps were ined to determine whether or not they supported the two replaced and their original calibrations were applied (data differing Optronic Laboratories calibrations for lamp F303. not shown). The calibration coefficients obtained for the There are caveats accompanying each SIRREX data set, BOPSII instrument using F219 with the manufacturer's which must be taken into account when interpreting SIRlamp calibration compared poorly to later data. When the REX data. During SIRREX-1 (July 1992), the required coefficients for instrument 8714 were recalculated using the uncertainty of 1% was not achieved when transferring the 1995 transfer calibration from lamp F304 to F219, there NIST scale of spectral irradiance from the Goddard Space was better agreement between early (pre-1992) and later '-Flight _center (GSFC) stan_arcl:iamp (F267) to the other calibrations. Similar to the BBOP instruments, when the lamps (Johnson et al. 1996). The data are, however, in- July 1995 Optronic Laboratories calibration of F303 was cluded here for completeness, and this goal was achieved used for all radiometer calibrations from 1992-1995, the during SIRREX-2 and -3. During SIRREX-3, a recent agreement was much better (see below); in fact, 19 out of NIST calibration of the standard lamps (GSFC lamps F268 21 channels varied less than 1%. and F269) became available and indicated that the output The requirement that radiometer calibrations be accu- of lamp F269 had drifted by approximately 1.5% somerate, as well as stable, and the problems of reconciling dif- time during the previous year, likely as early as SIRREX-2 34

Original page 41

O'Reillyet al. (Muelleret al. 1996).Thisnecessitateda recalculationof un- the original Optronic Laboratories F219 calibration and theSIRREX-2datasets,andincreasedtheircombined Lamp F219: There was very poor agreement between bethe mostreli- the earliest SIRREX data (SIRREX-1), but these dates certainty.The SIRREX-3resultsshould experiencedwere three years apart. The agreement was better between ablebecausemanyoftheproceduralproblems wererectifiedandthe the derived F219 calibrations and SIRREX-2 in the visible duringthe first two experiments by NISTonlyonemonth region (Table 9). standardlampswerecalibrated previously. In general, the SIRREX data supported the same conduringthe clusions as the radiometer comparisons: namely, that F303 Eachlamp'sirradiance,atwavelengthsused Lagran- (1995 calibration ) and F304 agree and that the 1995 trans- SIRREXs,wascomputedusingtherecommended and fer calibration of F304 to F305 and F219 was reliable (data gianinterpolationproceduret.Whenthe SIRREX-2 -3 datafor lampsF304andF305werefirst compared,shown below). The SIRREX data do not support well the of 1.6% 1992 Optronic Laboratories calibration of lamp F303. it appearedthe SIRREX-2datawereanaverage 400-1,000nm, Because the 1995 Optronic Laboratories F304 calibralowerthanthosefromSIRREX-3between standardtion seems to be the touchstone for the other lamp caliwhichsupportsthedriftobservedin theSIRREX for brations, one additional comparison was examined to conlampsdescribedby Muelleret al. (1996).Tocorrect to SIRREX-3firm its absolute values. A BSI PRR (S/N 9626) with this drift, the averageratiosof SIRREX-2 for bothlampsF304andF305be- the same type of photodiodes as the MERs was used for datawerecomputed tween400 and 1,000nm and this factor applied to the SIRREX-2 data for all lamps and all wavelengths. The ratio between SIRREX-2 and -3 can be computed only for lamps F304 and F305 because they had not been used between these two experiments. Each calibrated lamp's output was compared to the irradiance measured at each SIRREX experiment (Fig. 20 and Table 9). To examine the performance of lamps for which there was no current manufacturer's calibration, lamp irradiances were computed from the transfer calibrations (performed at UCSB) from F304 to F219 and F305. These were confined to wavelengths between 380 and 665 nm. Lamp F303: In general, there was best agreement between each SIRREX experiment and the closest Optronic Laboratories calibration for lamp F303 (Fig. 20a). The color shift between 1992 and 1995 suggested by the Optronic Laboratories calibrations, however, was not confirmed at either SIRREX-2 or SIRREX-3. The SIRREX-2 (1993) data for F303 between 400 and 700 nm did not agree well with either the original 1992 data or the 1995 data (1.6 versus 2.1%, Table 9). There is good agreement above 400nm between the SIRREX-3 (1994) and the 1995 Optronic Laboratories calibration of lamp F303 (0.7%, Table 9). It should be noted that during SIRREX-3, F303 was calibrated against the standard lamp F268, which was recently calibrated by NIST, rather than F269 which was observed to shift in irradiance during the experiment (Mueller et al. 1996). A change in the output of F303 could not be inferred from the SIRREX results. Lamps F304 and F305: The Optronic Laboratories calibration of lamp F304 (1995) and the derived calibration of F305 compared well with both the SIRREX-2 and the SIRREX-3 data for these lamps, 0.8 and 1.0%, respectively (Fig. 20b and Table 9). t This was from an internal Optronic Laboratories report titled "Report of Calibration of One Standard of Spectral Irradiance OL FEL-C, S/N: F-304," Project No. 903-479, 28 July 1995. one of the training sessions at SIRREX-4 (May 1995) at NIST. Although the setup was not optimal, readings were taken with two FEL lamps, F423 and F422 (owned and calibrated by NIST). Using the F304 Optronic Laboratories calibrations to compute irradiances for the two NIST lamps, the agreement was within 1% for all but one value at 665 nm, where the disagreement was most likely due to reflected stray light from the dark color of the baffling on the calibration bench (Table 10). This instrument had been calibrated in March, May, and August 1995 at UCSB, and in May 1995 at BSI, and these calibrations also agreed within 1% at all wavelengths (data not shown). The Optronic Laboratories F304 and F303 calibrations in July 1995 were in good agreement with the data from two SIRREX experiments in 1993 and 1994, as well as with data from two NIST calibrated lamps in 1995. Based on the radiometer responses, it appears that the irradiance of F303 had not changed since 1992. The excellent consistency between the early radiometer calibrations calculated with the 1995 Optronic Laboratories calibration of lamp F303 and those done with F304, since July 1995, support the hypothesis that the 1992 Optronic Laboratories calibration for lamp F303 was not accurate and should not be used. Rather, it appeared that the 1995 Optronic Laboratories F303 calibration should be used for all radiometer calibrations with this lamp. For all subsequent discussions, the 1995 Optronic Laboratories irradiances for lamps F303 and F304 will be used for the BBOP radiometers' calibrations from 1992 to mid-1995 (F303) and from mid-1995 to the present (F304). 4.3.3 Irradiance History Once it was established which lamps and calibrations were most reliable, all of the calibrations of two UCSB profiling radiometers (S/N 8728 and 8714) could be examined in detail. Because of their different use and calibration timelines, the irradiance histories of these two radiometers will be discussed separately. 35

Original page 42

SeaWiFS Postlaunch Calibrationand ValidationAnalyses, Part 3 a) • 1.05 "mPI,e_pefj_ll'eeeeeeee• • • SIRREX 1: Optronics92 • SIRREX2:Optronics92 • SIRREX3:Optronics92 " SIRREX 1: Optronics95 o SIRREX2:Optronics95 o SIRREX3:Optronics95 4•'b, A-"4,4,6,.... nimlggmlllm_llll_e:[nmn•nnauuu•nUnnamUnmnuUUg ! ...a .......... m3 _ ................... 10(!)0 00000000000000 O0 1.00 oUOOOOOooOOe_oOOOon OOr, noOOoon^_ _ 0 _ ',.'u 001: O00_l_ 0 000_ a _ °(I_I°°°_ O00000000oOOA °°°°°°°°OC 0.95 t I n I n I b) • ,,,i "1 O 1.05 "0 _ 1.00 0.95 I l I u I _ 1.02 c) "3 1.01 , 1.00 n I i I i I I [] SIRREX2:Optronics95 o SIRREX3:Optronics95 J i 1 I I i L,,. u e SIRREX2:Transfer e SIRREX3:Transfer oO oooo°ooooo:° , v _:_NNN_N_NN_N N m N _ 0.99 N 0.98 ® I , I I 400 500 600 Wavelength [rim] I t I L I u 700 800 900 1000 Fig. 20. Ratios of SIRREX results to Optronic Laboratories irradiances for three lamps used at the ICESS Calibration Facility: a) Lamp F303, ratios of three SIRREX irradiances to Optronic Laboratories calibrations from two dates, in 1992 and 1995; b) Lamp F304, ratios of two SIRREX irradiances to Optronic Laboratories calibration from 1995; c) Results from SIRREX-2 and -3 compared to the transfer calibration of F304 to F305, note scale change. 36 z m

Original page 43

O'Reilly et al. Table 10. Comparison of computed irradiances for lamps F422 and F423 measured during SIRREX-4 [/(X)] using PRR S/N 9626 [E'(A)] as the transfer radiometer. are also given. F422 Irradiance The percent differences (PD) from the actual irradiances F423 Irradiance X [nm] /(X) /'(),) PD [%] E(X) /'(),) PD [%] 412 2.6004 2.5827 -0.69 2.7239 2.7132 -0.40 443 3.9873 3.9513 -0.91 4.1652 4.1490 -0.39 490 6.5817 6.5255 -0.86 6.8502 6.8224 -0.41 -0.94 8.1107 8.0559 -0.68 510 7.8034 7.7309 555 10.6600 10.5983 -0.58 11.0500 11.0274 -0.21 665 17.0185 16.7927 -1.34 4.3.3.1 BBOP Radiometers To compare the differences among irradiance calibrations over the entire project, each detector's coefficient was normalized to that from the first calibration in July 1992. 17.5592 17.4974 -0.35 4.3.3.2 BOPSII Radiometer The calibration history of the BOPSII profiling radiometer (S/N 8714) began in February 1989 using lamp F219 (Fig. 17). In October 1992, lamp F303 replaced F219, The gains of underwater instrument 8728 were adjusted in which was in turn replaced by F304 in October 1995. For early 1994 and so later data were renormalized to the first calibration after this date. b-Yom 1992-1996, most of the channels of the profiling radiometer (S/N 8728) were very stable with no appreciable trends (Fig. 21a). The scatter of all channels, however, increased from January 1994 to December 1996, up to about 2%. The differences between slopes calculated on any two consecutive dates were calculations with lamp F219, the transfer calibration from F304 to F219 was used. The 1995 Optronic Laboratories calibration for lamp F303 was used for all calibrations performed with that lamp. The data were treated similarly to that for the BBOP radiometer. Slopes were normalized to the January 1994 value. Most downwelling irradiance detectors showed similar variations to those in instrument small, about 0.2%. On two dates (9 August 1994 and 19 8728 (Fig. 23). During seven years, most calibration slopes December 1996), calibrations were performed using both lamps F303 and F304 and the calibration coefficients were nearly identical. Those detectors, which did not remain stable to within 2% during four years, had shown marked deterioration (up to 5% in three months) and have been replaced (Fig. 22 and Sect. 4.4). There was a slight drift downwards in some of the blue channels, indicating that these detectors may have begun to deteriorate. The original BBOP surface sensor (S/N 8729) was very stable from 1992-1994, but drifted towards increasing sensitivity during 1994-1995 (Fig. 21b). The last calibration before instrument 8729 was taken out of service agreed well with the calibration performed in early 1997, about two years later. Except for the most recent calibration (1997), lamp F303 was used for all cMibrations of instrument 8729. There were no repairs or physical events that would explain the drift. Its replacement (S/N 8734) also showed a similar drift upward during 1995-1996, but has been stable since mid-1996 (Fig. 21c). In May 1996, a smudge of O-ring grease was cleaned from under the Teflon(_t cosine collector, which was likely to have been the cause of the drift. Calibrations after this event were renormalized to the May 1996 values; since then, the instrument 8734 calibrations have been very stable (Fig. 21c). The two UV channels, Ea(340) and Ea(380), have shown marked deterioration and have been replaced (data not shown). Teflon is a registered trademark of E.I. du Pont de Nemours, Wilmington, Delaware. for each channel were within 2%; in fact, 19 out of 21 channels varied less than 1%. Two detectors, Ed(510) and Ed(520), however, still showed large, unexplained drifts from 1989-1992. 4.3.4 Radiance History The radiance calibration history is longer for the integrating sphere than for the plaque, however, the reflectance of this sphere has never been satisfactorily characterized and an arbitrary reflectance value was used in the slope calculations. From mid-1994 through 1996, the radiance channels of instrument 8728 were calibrated with both the sphere and the plaque, so the plaque calibrations could be transferred onto the earlier sphere calibrations. Plaque radiance values were computed from the lamp irradiance corrected for the inverse square law, the manufacturer's determination of the plaque's reflectivity (provided at the time of purchase), and the assumed Lambertian distribution. Calibration coefficients for instrument 8728 were normalized to those from August 1994, the first date on which plaque calibrations were performed (Fig. 24a). As with the irradiance history, most of the ra. diance channels showed very little change. On instrument 8728, 10 out of 12 channels varied less than 1% from the normalized value during 10 calibrations (the range for all channels was 0.26-1.55%). Figure 24a also shows a slight decrease in the blue channels during 1995 and 1996, although the overall decrease is still less than 2%. 37

Original page 44

SeaWiFS Postlaunch Calibration 1.03 a) 1.02 1.01 [] [] o 1.00 0.99 norm / 7 0.98 i 1.03 b) © °,,_ ca 1.02 8 _9 O 1.01 v A and Validation Analyses, Part 3 0 8 _ O 8 o_8 [] 8 o [] e A A O V O V & V 8o v v _7 v v • I i 1 ! I I I I I 8 _7 _7 O O A o Ed(410) 1.00 .... _ -- -- -0 .... 9 N 0.99 °1,, norm 0 0.98 O O Z • i I i i | i. 1.04 c) 1.03 1.02 1.01 l.O0 El- 0.99 i • L L l I i 1992 1993 1994 : : 77 v Ea(441) O [] Ea(488) 0 Ea(520) a Ea(565 ) | | t i | i 0 Ed(683) [] 0 O [] [3 A O O .... norm i I I i I _ i l l ] 1995 1996 1997 1998 Year Fig. 21. The normalized calibration Coefficients for selected downweliing irradiance channels on three BSI MER-2040 and -2041 radiometers used during BBOP computed using the 1995 Optronic Laboratories calibrations of F303 and F304: a) underwater instrument (S/N 8728), b) surface sensor (S/N 8729), and c) surface sensor (S/N 8734). 38

Original page 45

O'Reilly 665 i.0 et al. -e-.--- *----lg---$-A _ _ | _ [] ® ® [] & & [] [] 0.9 [E ® E,(510) © 0.8 & Ed(555) IE Ed(665) 0.7 a) O i I I I I .... L 1.0 -- 9 N 0.9 [] [] O [] Z 0.8 0.7 b) 0.6 t |, I i i I 1992 1993 1994 ® [] ® [] [] I i I I .a i i i t -- I----- - B ® ® m B ® t_(510) L_(555) IE I_(665) i i _J J . 1 I i i I 1995 1996 1997 1998 Year Fig. 22. Deteriorating detectors on the BBOP radiometers (S/N 8728 and 8734) from 1992-1997. The arrows indicate when detectors were replaced. 1.15 % O 1.10 9 O <> 1.05 ¢} 1.00 v$ O oO Z 0.95 , , , O Ed(410) X7 Ed(441) rn E(488) O Ea(520) /x Ea(565) O Ed(665) (> norm I I t t z 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 Fig. 23. The normalized calibration coefficients BOPSII profiling radiometer (S/N 8714) calculated Year for selected downwelling irradiance channels on the with the transfer calibration of F304 to F219 and the 1995 Optronic Laboratories calibrations of lamps F303 and F304. 39

Original page 46

SeaWiFS Postlaunch Calibrationand ValidationAnalyses, Part 3 1.02 1.01 1.00 0 no / O- § 0.99 °¢=q o 0.98 L_ 0 Lu(410) a) O v v v v v v O O O 0 0 0 0 O 0.97 V t.(44]) "z_ 0 | o L,(488) t , I • ! 1.10 0 h(520) V L) 0 1.08 A L,(565) 0 I_(683) .plw 1._ r3 1._ 0 O 7 norm Z 1.02 1. .... 0.98 0.96 0._ b) 0._ I , • I _ 1992 1993 i994 for selected radiance channels on the BBOP radiometer Fig. 24. The normalized calibration coefficients (S/N 8728) from 1992-1997: a) reflectance plaque, .... [] v n v v v n B v 0 v 0 0 0 80 ° o o , 1 I I I i n I I 1995 1996 1997 1998 Year and b) integrating sphere. Sphere coefficients were normalized twice, because of September 1996, it was assumed that the nominal plaque the gain change in January 1994. Coefficients from calibrations before the gain change were normalized to the to units of V roW- l cm nm sr) for the measured sphere volt- December 1992 calibration, and those from later dates the August 1994 data--the same date as plaque normalizations (Fig. 24b). Over the long term, calibrations with the sphere were more variable than those with the plaque. From August 1994 to September 1996, the same 10 channels discussed above had an average coefficient of variation (CV) of 1.4% when calibrated with the sphere. The plaque and sphere were illuminated by the same lamp, so the greater variation in the sphere calibrations may have been due to changes in the back loading of the sphere when the instrument was positioned close to the exit aperture, or to changes in the reflectivity of the sphere coating. These possibilities were examined before the plaque calibrations were transferred onto the earlier sphere calibrations. Because the lattei plaque data are very stable, two plaque calibrations were used to examine possible shifts reflectances were correct. These were used to compute the sphere reflectances that would yield the same slopes (in ages as were measured with the plaque (Fig. 25). The difference between the nominal and calculated sphere refiectances was clearly spectral and ranged from 0.-0.83% in May 1995, and from 0.24-0.68% in September 1996. The differences between the 1995 and 1996 calculations were generally less than 0.2%. Although the differences between the two computed reflectances were greatest in the blue region, the changes were not large enough to suggest that the reflectivity of the sphere had changed during this time. When the two estimated sphere reflectances were used to calculate calibration slopes, their differenc were magnified to approximately 2% (Table 1i). Because the differences between the two computed sphere reflectances were small and within the reproducibility of the sphere calibrations, and any differences would be magnified ff a single estimate of sphere reflectance was used, the averin sphere reflectance. For two dates, 17 May 1995 and 18 age ratio of plaque-to-sphere coefficients was computed for 4O

Original page 47

O'Reilly 0.9850 0.9825 0.9800 • A 0.9"/75 0.9750 I I 400 450 500 Wavelength [nm] et al. 00 • A A Measured May 95 • Measured Sep 96 i I I 550 600 650 700 Fig. 25. Computed reflectance of the ICESS integrating sphere on two dates, 17 May 1995 and 18 September 1996. The dashed line shows the manufacturer's nominal reflectance. each channel. These factors were applied to the average calibration slopes measured with the sphere in 1992 and 1993. Table 11. Radiance calibration slopes for radiometer 8728 measured on'18 September 1996 computed from sphere reflectances estimated on two dates, May 1995 and September 1996. The units are in V pW- l cm 2 nm sr. A [nm] May 95 Sept. 96 PD [%] 410 0.90070 0.87252 3.13 441 0.93630 0.90027 3.85 465 0.86910 0.84426 2.86 490 0.88819 0.86418 2.70 510 0.85202 0.83449 2.06 520 0.87318 0.85510 2.07 555 1.03165 1.01033 2.07 565 0.90756 0.88888 2.06 589 0.86213 0.84250 2.28 625 0.90776 0.89353 1.57 665 1.08689 1.08205 0.45 683 0.99982 0.98244 1.74 This examination of the calibration histories of these radiometers demonstrated that most of the detectors were stable over the course of these instruments' 6-8 year histories. Furthermore, the stability of the calibration coefficients also implies stability of the amplifiers, analogto-digital converters and optical windows of the MER instruments, as well as, reproducibility of calibration lamp geometry and the lamp power supply. A change in any of these components would have been evident in the calibration coefficients. Their absolute calibrations, however, are tied to just one lamp calibration by Optronic Laboratories (F304 in May 1995), which itself, is guaranteed to about 1%. The variety and number of comparisons of lamp F304's irradiance to other lamps lend confidence to these values. 4.4 LONG-TERM AVERAGES Long-term averages of calibration slopes can be computed with confidence, because the radiometers used with BBOP appear to be very stable. These long-term averages should be used whenever possible and recomputed after major upgrades. Calibration coefficients for deteriorating channels should be interpolated. For these purposes, stability has been defined by a CV less than 1%. When the CV exceeded these limits, the calibration data were examined closely for trends or shifts and, in most cases, a physical reason for the change was evident which justified computing a new long-term average. Tables 12-14 summarize the slopes that will be used for most channels on the three BBOP radiometers. For the profiling radiometer (Table 12), there are two main time periods: 1992-1993 during which there were a total of 15 channels, and 1994-1996 after the upgrade to 12 downand 13 upwelling channels. In most cases, one slope can be used for each channel for each time period. At the end of 1994, both 555 nm detectors were replaced and the slopes of several other channels were affected as well: Ed(488), 41

Original page 48

SeaWiFSPostlaunchCalibrationandValidationAnalyses,Part3 Table 12. Theaveragecalibrationslope(ACS)valuesusedfor MER-2040(S/N8728)from1992-1996.The CV andthenumberofobservations(n) arealsogiven.Formostchannels,onlytwoslopesarenecessary:before andafterthegainchangein January1994.Thetophalfofthetablegivestheaveragecalibrationslopesforthe downwelledirradiancechannels,Ed(A), in units of VpW -1 cm 2 nm. For the channels affected by the repairs in January 1995 [Ed(410), Ed(488) and Ed(520)], it was necessary to compute separate averages for 1994 and 1995-1996. Before plaque calibrations were available, the average slopes for the upwelled radiance channels, Lu(A) (in units of VpW -1 cm2nmsr) were determined using the mean slope from the sphere calibrations and the plaque-to-sphere ratios (given in the bottom half of the table). Their CVs were calculated from the uncorrected sphere calibrations. Measurement 1992-1993 1994-1996 1994 1995-1996 Channel A CS CV n A CS Ed(410) 0.04796 0.21 5 E.(441) 0.04568 0.23 5 0.03517 Ed(465) 0.04855 0.14 5 0.03248 Ed(488) 0.05436 0.42 5 Ed(510) [] Ed(520) 0.04894 0.27 5 E.(555) [] Ed(565) 0.05456 0.20 5 0.03409 E_(587) 0.05556 0.16 5 0.03548 E_(625) [] Ed(665) [] Ed(683) [] CV n A CS CV n A CS CV n 0.03256 0.70 7 0.03211 0.90 3 0.94 15 0.68 15 0.03395 0.51 4 0.03450 0.46 11 0.03411 0.37 6 [] 0.03314 0.47 4 0.03370 0.56 11 [] 0.03633 0.97 11 0.67 15 0.80 15 0.03626 O.52 4 0.03684 0.48 11 0.03449 0.59 4 [] 0.03498 0.48 4 0.03563 0.56 11 Lu(410) 0.3482 0.38 3 0:8917 -=°==1.47 °° 11 L_(441) 0.2800 0.69 3 0.9111 L_(465) 0.3071 0.42 3 0.8301 L_(488) 0.2804 0.52 3 0.8561 L_(510) [] L_(520) 0.2523 0.59 3 0.8560 L_(555) [] L_(565) 0.2476 0.59 3 0.8898 L_(587) 0.2440 1.04 3 0.8505 L_(625) [] 0.8967 L_(665) [] Lu(683) 0.2379 0.83 3 0.9819 [] Not applicable. [] Indicates that a detector was deteriorating, e.g., Ed(665), 0.65 11 0.38 11 0.43 11 0.8843 0.41 4 [] 0.30 11 0.8921 0.01 2 1.0198 0.96 8 0.26 11 0.40 11 0.29 11 0.8814 0.87 4 [] 0.28 11 and no average could be computed for that time period. Table 13. The ACS values used for MER-2041 (S/N 8729) from 1992 to August 1995, in units of VpW -1 cm 2 nm. l_Ieasurement Sept. 1992-Aug. Channel ACS CV Ed(410) 0.02564 .91 Ed(441) 0.02587 .28 Ed(488) 0.02934 .22 Ee(520) 0.03037 .28 Ed(565) 0.03163 .42 Ed(665) 0.03492 .55 42 1994 Aug. 1994-1995 n ACS CV n 7 0.02566 .68 3 7 0.02635 .42 3 7 0.03002 .45 3 7 0.03094 .44 3 7 0.03213 .55 3 7 0.03539 .49 3

Original page 49

O'Reillyet al. Ed(520), Ed(625), and Ed(683). For these channels, new long-term averages were computed for 1995-1996. Several detectors--Ed(510), E_(555), Ed(665), L_(510), and L_ (665)--deteriorated (Fig. 22), and it was not possible to calculate their average slopes for many months. For these channels, the deterioration was assumed to be linear and a slope was calculated for each cruise using a least-squares regression. During 1996 and 1997, all of these aging detectors were replaced and new long-term averages must be determined. Table 14. The ACS values used for MER-2041 (S/N 8734) from August 1995-1997 (in units of V #W-1 cm 2 nm). No average could be computed for the time period of May 1995-1996 because of the drift of the instrument's response. For the Ed(340) channel, the mean is for the time period of Decem- )er 1996-August 1997. May 1996-Aug. 1997 Channel A CS CV n Ed(340) 0.01496 2.12 3 Ed(380) 0.00538 0.31 6 Ed(410) 0.02477 0.40 6 Ed(441) 0.02888 0.41 6 Ed(465) 0.02049 0.38 6 Ed(488) 0.01534 0.51 6 Ed(520) 0.01617 0.40 6 Ed(540) 0.01278 0.41 6 Ed(565) 0.01108 0.47 6 Ed(587) 0.01257 0.36 6 Ed(625) 0.01411 0.36 6 Ed(665) 0.01581 0.36 6 Ed(683) 0.01499 0.32 6 The calibration coefficients of the two surface sensors (S/N 8729 and S/N 8734) appear to have drifted since 1992 (Figs. 21b-c, Sect. 4.3.2.1). For these, long-term averages will be used only for time periods when the responses for these instruments were stable. For instrument 8729, the overall drift (1992-1995) was about 2% (Fig. 21b), but the CV of the average slopes can be reduced to less than 1% by dividing the data into two time periods and calculating means for each (Table 13). There was no obvious physical reason for this drift. Radiometer 8734 drifted about 3-4% from May 1995 to May 1996, because of the grease accumulating under the cosine collector (Fig. 21c). Because the CVs during its first year of use were well over 1%, it was assumed that the drift was linear and the calibration slopes were interpolated as for deteriorating detectors. For calibrations after May 1996, the slopes were very steady and long-term averages can be used (Table 14). For most detectors, the average slope calculated for years 1994-1996 (instrument 8728) or for 1995-1996 (instruments 8729 and 8734) will also be applicable to future data. The methods used here to examine past stability will accommodate the addition of new calibration data as it is available; it will be possible to closely track any changes in the performance of these instruments and adjust the calibration coefficients accordingly. 4.5 OTHER ISSUES Although calibration lamp behavior was the first consideration when examining differences between calibrations, several other factors are involved in determining the final calibration coefficents. These may affect all of the coefficients calculated for a particular instrument (e.g., the effect of immersion on the cosine collector), or, like the lamp calibrations, may change over time (e.g., aging of the reflectance plaque). 4.5.1 Immersion Effects The effect of immersion in water on acrylic cosine collectors is to decrease the irradiance responsivity of the radiometer compared to that measured in air. It has been determined experimentally that the immersion effects of different cosine collectors of the same design and material may differ by as much as 10% (Mueller 1995b). This makes questionable the practice of applying one immersion coefficient, which is based on material and design specific.ations, to all collectors in a class. The immersion coefficients for the BOPSII and BBOP profiling instruments were measured at SDSU CHORS during 1994 and 1995, respectively (Mueller 1995b, and Mueller 1996). The final immersion coefficients for instrument 8728 were predicted from the linear regression (441-625 rim) or were the average of two measurements of immersion (for 410, 665, and 683 nm). The final immersion coefficients for instrument 8714 were predicted from the linear regression. Nominal immersion coefficients (provided by the manufacturer) and those determined at CHORS for these two instruments are presented in Table 15 and Fig. 26. Differences from the nominal values ranged from 3.5-10%. A single, nominal immersion coefficient cannot be applied to all instruments and possibly, several measurements of the immersion effect must be performed on a single instrument to determine an accurate coefficient. Uncertainties of 10% in accuracy or reproducibility are unacceptable for vicarious calibration. The measured immersion coefficients reported in Table 15 have been used for all calculations of calibration slope during BBOP. It is likely that when the immersion coefficients for the BBOP instrument have been more clearly defined by additional immersion tests that these calibration slopes will be recalculated. 4.5.2 Possible Plaque Aging Figure 24a showed a slight decrease in the slopes of the blue channels on instrument 8728 during 1996, although the decrease was small--less than 2%. It is possible that the plaque is yellowing or becoming soiled, or that the 43

Original page 50

SeaWiFS Postlaunch Calibrationand Validation Analyses,Part 3 Table 15. Immersion coefficients(I/F,) forradiometers used in thisstudy (from Mueller 1995b and Mueller 1996). The nominal valueswere provided by the manufacturer (BSI) at the initialcalibrationof instrument 8728. The column headings denote the MER model and serialnumber, and the collectortype, eitherEd or Eu (upwelledirradiance). A [nm] Nominal (Nominal) Immersion 410 0.705 441 0.694 465 0.691 488 0.691 510 0.694 520 0.695 555 0.705 565 0.708 587 0.715 625 0.726 665 0.736 683 0.739 0.82 0.80 0.78 00 _ 0.76 • v_ i 0.74 0 0.72 0.70 I 0.68 I 400 450 500 Wavelength [nm] 2040 (S/N 8728) 2040 (SIN 8714) E_ E_ E_, 0.7856 0.71311 0.71592 0.7637 0.71911 0.72351 0.7688 0.7736 0.72796 0.73498 0.7785 0.73998 0.7803 0.73578 0.74275 0.7885 0.7907 0.74528 0.75464 0.7958 0.75050 0.76090 0.8042 0.75915 0.77129 0.7642 0.7870 0 O __7 -- O 8714 N V 8714 Eu 28 Ed 1 Nominal i I I 550 600 650 700 Fig. 26. The nominal and measured immersion coefficients for three irradiance heads on two radiometers. 44

Original page 51

O'Reilly 1.010 I • F304toF303 ] 7 F304toF305 I 1.005 t t-, 1.000 @ o_ 7 v D 0.995 0.990 f _ i 400 450 500 Wavelength [nm] Fig. 27. The ratio of transfer calibrations performed F304, to lamps F303 and F305. two blue detectors, L(410) and L,(441), are deteriorating. Because calibrations of other recently purchased instruments are being monitored at ICESS, this question will be clarified. In addition, the plaque is scheduled to be recMJbrated by the manufacturer in the near future. 4.5.3 Quality Control Measures These results precipitated refinements in calibration methods and record keeping at ICESS. First, to avoid possible confusion when standard lamps are replaced, lamps dedicated to each project were purchased so that the consistency of calibrations can be monitored easily for many years. Second, annual in-house cross-checks between lamps were initiated in 1995. The transfer calibration performed from lamp F304 to F305, and F303 in May 1995 was repeated in May 1996 (Fig. 27). With one exception, lamp F305 at 465 nm, the differences between the two transfers one year apart were less than 0.5%, implying that the output of these three lamps had not changed during the year following the 1995 lamp calibration at Optronic Laboratories. The agreement was particularly good between lamps F303 and F304. In fact, this 465 nm detector [S/N 8733, Ed(465)] was recently replaced after it was determined to be unstable. Lamp F303 was retired from routine calibrations in 1995 and now serves as a standard to which any other lamp's performance can be compared. Transfer calibrations such as these will of suit, there can be confidence in its accuracy. It is essential be continued annually to closely monitor performance lamps between routine calibrations at the manufacturer and future SIRREX workshops. et al. v v v i i I 550 600 650 700 in May 1996 to those from May 1995 from lamp 4.6 CONCLUSIONS The variations of calibration slopes for most channels of radiometer 8728 were less than 1% between 1992 and 1997. Because the radiometers used for BBOP appear to be very stable, there can be excellent confidence in the long-term averages of calibration slopes and consequently, in the AOPs produced from profile data. These long-term averages should be used whenever possible. When the 1995 calibrations of lamps F303 and F304 were used to calculate slopes, there was an almost seamless transition when F304 replaced F303 as the primary lamp for radiometer calibrations. The methods used here to examine past stability, accommodate the addition of new calibration data as they become available, enabling close monitoring of changes in instrument performance, and the necessary adjustment of calibration coefficients. These results show that there can be confidence in the calibration of the MER-2040 series radiometers at the 1% level. It appears, however, that the calibration responses of these instruments may have been more stable than the irradiance of the lamps used as calibration standards. Ultimately, the absolute calibrations of the radiometers discussed here are tied to one lamp calibration by Optronic Laboratories at the midpoint of this time series, which itself, is guaranteed to about 1%. That calibration has been compared with as many others as possible, and as a rethat comparisons such as these continue to ensure the high quality of radiometer data. 45

Original page 52

SeaWiFS Postlaunch Calibration GLOSSARY ALOHA A Long-term Oligotrophic Habitat Assessment [the Hawaii Ocean Time-series (HOT) deepwater station located about 1001on north of Oahu, Hawaii]. ACS Average Calibration Slope AI9901 Atlantic-Indian Ocean Cruise, 1999 AMT Atlantic Meridional Transect AOP Apparent Optical Properties BATS Bermuda Atlantic Time Series BBOP Bermuda BioOptics Project Ber95 Bering Sea Cruise, 1995 Ber96 Bering Sea Cruise, 1996 BOPSII Bio-Optical Profiling System II (second generation) BSI Biospherical Instruments, Inc. CalCOFI California Cooperative Oceanic Fisheries Investigation CARIACO Carbon Retention in a Colored Ocean CB-MAB Chesapeake Bay-Middle Atlantic Bight CDOM Colored Dissolved Organic Matter CHORS Center for Hydro-Optics and Remote Sensing COARE Coupled Ocean Atmosphere Response Experiment COASTS Coastal Atmosphere and Sea Time Series CoBOP Coastal Benthic Optical Properties (Bahamas) CSC Coastal Service Center, (NOAA, SC) CV Coefficient of Variation CVT Calibration and Validation Team CZCS Coastal Zone Color Scanner DARR Data Analysis Round-Robin (workshop) EcoHAB Ecology of Harmful Algal Blooms EqPac Equatorial Pacific FEL Not an acronym, but a type of irradiance lamp designator. FL-Cuba Florida-Cuba cruise. FWHM Full-Width at Half-Maximum GOM Gulf of Maine GoA97 Gulf of Alaska Cruise, 1997 GSFC Goddard Space Flight Center HOT Hawaii Ocean Time-series HPLC High Performance Liquid Chromatography ICESS Institute for Computational Earth System Science IDL Interactive Data Language JES9906 Japan East Sea Cruise, 1999-06 JGOFS Joint Global Ocean Flux Study Lab96 Labrador Sea Cruise, 1996 Lab97 Labrador Sea Cruise, 1997 Lab98 Labrador Sea Cruise, 1998 LTER Long Term Ecological Research MCP Modified Cubic Polynomial MBARI Monterey Bay Aquarium Research Institute MBR Maximum Band Ratio MER Marine Environmental Radiometer MERIS Medium Resolution Imaging Spectrometer MF0796 R/V Miller Freeman Cruise, 1996-07 MOCE Marine Optical Characterization Experiment MODIS Moderate Resolution Imaging Spectroradiometer 46 and Validation Analyses, Part 3 NABE North Atlantic Bloom Experiment NASA National Aeronautics and Space Administration NEGOM Northeast Gulf of Mexico NIST National Institute for Standards and Technology NOAA National Oceanic and Atmospheric Administration OC2 Ocean Chlorophyll 2 algorithm OC2v2 OC2 version 2. OC4 Ocean Chlorophyll 4 algorithm OC4v2 0C4 version 2. OC4v4 OC4 version 4. OCTS Ocean Color and Temperature Scanner ORINOCO Orinoco River Plume PD Percent Difference PRR Profiling Reflectance Radiometer RED9503 Red Tide Cruise, 1995-03 Res94 Resolute Cruise, 1994 Res95-2 Resolute Cruise, 1995 Res96 Resolute Cruise, 1996 Res98 Resolute Cruise, 1998 RMS Root Mean Square ROAVERRS Research on Ocean-Atmosphere Variability and Ecosystem Response in the Ross Sea SDSU San Diego State University SeaBAM SeaWiFS Bio-optical Algorithm Miniworkshop SeaWiFS Sea-viewing Wide Field-of-view Sensor SIMBIOS Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies SIRREX SeaWiFS Intercalibration Round-Robin Experiment SIRREX- 1 The first SIRREX, July 1992. SIRREX-2 The second SIRREX, June 1993. SIRREX-3 The third SIRREX, September 1994. SIRREX-4 The fourth SIRREX, May 1995. SMAB Southern Mid-Atlantlc Bight S/N Serial number SNR Signal-to-Noise Ratio SPO SeaWiFS Project Office TOGA Tropical Ocean Global Atmosphere TOTO Tongue of the Ocean study (Bahamas) UCSB University of California, Santa Barbara URL Universal Resource Locator UVA Ultraviolet-A WOCE World Ocean Circulation Experiment SYMBOLS a Absorption coefficient. A Coefficient. aw Absorption coefficient for pure water. b Intercept. B Coefficient. bb Backscattering coefficient. b_ Backscattering coefficient for pure water. Co Chlorophyll a concentration. Co In situ chlorophyll a concentration. Z

Original page 53

O'Reilly Irradiance measured during SIRREX-4. Irradiance measured using a PRR as the transfer radiometer. Downwelled spectral irradiance. Upwelled spectral irradiance. f Function. FI Immersion coefficient. K(490) Diffuse attenuation coefficient at 490 nm. K,(A) Diffuse attenuation coefficient for pure water. L(z,) Upwelled spectral radiance. Lw()) Spectral water-leaving radiance. Lw()l) Water-leaving radiance for wavelength A1. Lw(,k2) Water-leaving radiance for wavelength 2. m Slope. n Number of observations. N Number of data sets. NF Number of fluorometric chlorophyll a sets. NH Number of HPLC chlorophyll a sets. R 2 Squared correlation coefficient. R2 loglo( R49o$55)- R2s 10glok_R 4900551, see Rac, where the argument of the logarithm is a shorthand representation for the maximum of the three values. In an expression such as R2s, the numerical part of the subscript refers to the number of bands used, and the letter denotes a code for the specific satellite sensors [S is SeaWiFS, M is the Moderate Resolution Imaging Spectroradiometer (MODIS), O is the Ocean Color and Temperature Scanner (OCTS), E is the Medium Resolution Imaging Spectrometer (MERIS), and C is CZCS]. R3c •loglo tR443000 > R52O't5sol, /LiE loglo(Rss0443 > R4905e0 > R51O_s60), see Rsc. l tR443 R 49° R s20' R40 Oglot, 560 > 500 > 5651,see R3c. R4s •loglo( XR443$ss > D49o,s55 > RSlO_s50), see R3c. R Rrs ratio constructed from band A divided by band B. Rrs Remote sensing reflectance. Rr_ In situ remote sensing reflectance. /r8 Interpolated remote sensing reflectance. R ' A compact notation for the Rr(Ai)/Rrs(Aj) band Aj ratio. x The abscissa. y The ordinate. z Depth. 7 log(C_). Wavelength. a Standard deviation. et al. REFERENCES Austin, R.W., and Petzold, T., 1981: The determination of the diffuse attenuation coefficient of sea water using the Coastal Zone Color Scanner. Oceanography from Space, J.F.R. Gower, Ed., Plenum Press, 239-256. Evans, R.H., and H.R. Gordon, 1994: Coastal zone color scanner "system calibration": A retrospective examination, J. Ceophys. Res., 99, 7,293-7,307. Firestone, E.R., and S.B. Hooker, 1998: SeaWiFS Prelaunch Technical Report Series Final Cumulative Index. NASA Tech. Memo. 1998-I0_566, Vol. 43, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 4-8. Gordon, H.R., and W.R. McCluney, 1975: Estimation of the depth of sunlight penetration in the sea for remote sensing. Appl. Opt., 14, 413-416. _, and K. Ding, 1992: Self-shading of in-water optical instruments, Limnol. Oceanogr., 37, 491-500. --, and M. Wang, 1994: Retrieval of water-leaving radiance and aerosol optical thickness over the oceans with Sea- WiFS: A preliminary algorithm, Appl. Opt., 33, 443-452. Gregg, W.W., and R.H. Woodward, 1998: Improvements in high frequency ocean color observations: Combining data from SeaWiFS and MODIS, IEEE Trans. Geosci. Remote Sens., 36, 1,350-1,353. Johnson, B.C., S.S. Bruce, E.A. Early, J.M. Houston, T.R. O'Brian, A. Thompson, S.B. Hooker, and J.L. Mueller, 1996: The Fourth SeaWiFS Intercalibration Round-Robin Experiment (SIRREX-4), May 1995. NASA Tech. Memo. 10_566, Vol. 37, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 65 pp. Kahru, M., and B.G. Mitchell, 1998a: Spectral reflectance and absorption of a massive red tide off Southern California. J. Geophys. Res., 103, 21,601-21,609. , and _, 1998b: Evaluation of instrument self-shading and environmental errors on ocean color algorithms. Proc. Ocean Optics XIV, Kona, Hawaii, S. Ackleson and J. Campbell, Eds., [Available on CD-ROM.] Maritorena, S., and J.E. O'Reilly, 2000: OC2v2: "Update on the initial operational SeaWiFS chlorophyll a algorithm." In: O'Reilly, J.E., and 24 Coauthors, 2000: SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3. NASA Tech. Memo. 2000-206892, Vol. 11, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 3-8. McClain, C.R., 2000: "SeaWiFS postlaunch calibration and validation overview." In: McClain, C.R., E.J. Ainsworth, R.A. Barnes, R.E. Eplee, Jr., F.S. Patt, W.D. Robinson, M. Wang, and S.W. Bailey, SeaWiFS Postlaunch Calibration and Validation Analyses, Part 1. NASA Tech. Memo. 2000-206892, Vol. 9, S.B. Hooker and E,R. Firestone, Eds., NASA Coddard Space Flight Center, Greenbelt, Maryland, 4-12. 47

Original page 54

SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3 , and G.S. Fargion, 1999: SIMBIOS Project 1999 Annual , and C.C. Trees, 1997: "Revised SeaWiFS prelannch al- Report, NASA Tech. Memo. 1999-209486, NASA God- gorithm for the diffuse attenuation coefficient K(490)." dard Space Flight Center, Greenbelt, Maryland, 128pp. In: Yeh, F,-n., R.A. Barnes, M. Darzi, L. Kumar, E.A. Early, B.C. Johnson, and J.L. Mueller, 1997: Case Studies Morel, A., 1974: "Optical properties of pure water and pure sea- for SeaWiFS Calibration and Validation, Part 4. NASA water." In: Optical Aspects of Oceanography, N.G. Jerlov Tech. Memo. 104566, Vol. 41, S.B. Hooker and E.R. Fireand E. Steemann Nielsen, Eds., Academic Press, San Diego, stone, Eds., NASA Goddard Space Flight Center, Green- California, 1-24. _, and S. Maritorena, 2000: Bio-optical properties of oceanic waters: a reappraisal. J. Geophys. Res., (submitted). Mueller, J.L., 1993: The First SeaWiFS Intercalibration Round- Robin Experiment, SIRREX-1, July 1992. NASA Tech. Memo. 104566, Vot. 14, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 60pp. , 1995a: "An integral method for analyzing irradiance and radiance attenuation profiles." In: Siegel, D.A., M.C. O'Brien, J.C. Sorensen, D.A. Konnoff, E.A. Brody, J.L. Mueller, C.O. Davis, W.J. Rhea, and S.B. Hooker, 1995: Results of the SeaWiFS Data Analysis Round-Robin (DARR-94), July 1994. NASA Tech. Memo. 104566, Vol. 26, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 44-52. , 1995b: "Comparison of irradiance immersion coefficients for several Marine Environmental Radiometers (MERs)." In: Mueller, J.L., R.S. Fraser, S.F. Biggar, K.J. Thome, P.N. Slater, A.W. Holmes, R.A. Barnes, C.T. Weir, D.A. Siegel, D.W. Menzies, A.F. Michaels and G. Podesta, 1995: Case Studies for SeaWiFS Calibration and Validation, Part 3. NASA Tech. Memo. 104566, Vol. 27, S.B. Hooker, E.R. Firestone, and J.G. Acker, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 3-15. , 1996:MER-2040 SN 8728: Irradiance Immersion Factors, CHORS Tech. Memo. 004-96, Center for Hydro-Optics and Remote Sensing, San Diego State University, San Diego, California, 3 pp. , B.C. Johnson, C.L. Cromer, J.W. Cooper, J.T. McLean, S.B. Hooker, and T.L. Westphal, 1994: The Second Sea- WiFS Intercalibration Round-Robin Experiment, SIR- REX-2, June 1993. NASA Tech. Memo. 104566, Vot. 16, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 121 pp. _, and R.W. Austin, 1995: Ocean Optics Protocols for Sea- WiFS Validation ' Revision 1. NASA Tech. Memo. 104566, 'VoL 25, S.B. Hooker, E.R. Firestonel and J.G. Acker, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 67 pp. _, B.C. Johnson, C.F. Cromer, S.B. Hooker, J.T. McLean, and S.F. Biggar, 1996: TheThird SeaWiFS Intercalibration Round-Robin Experiment (SIR- REX-3), 19-30 Sepbelt, Maryland, 18-21. O'Reilly, J.E., S. Maritorena, B.G. Mitchell, D.A. Siegel, K.L. Carder, S.A. Garver, M. Kahru, and C. McClain, 1998: Ocean color chlorophyll algorithms for SeaWiFS, J. Geophys. Res., 103, 24,937-24,953. Pope, R.M., and E.S. Fry, 1997: Absorption spectrum (380- 700 nm) of pure water, II. Integrating cavity measurements, Appl. Opt., 36, 8,710-8,723. Siegel, D.A., M.C. O'Brien, J.C. Sorensen, D.A. Konnoff, E.A. Brody, J.L. Mueller, C.O. Davis, W.J. Rhea, and S.B. Hooker, 1995: Results of the SeaWiFS Data Analysis Round-Robin (DARR-94), July 1994. NASA Tech. Memo. 104566, Vol. 26, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 58 pp. Smith, R.C., and K.S. Baker, 1981: Optical properties of the clearest natural waters (200-800 nm). Appl. Opt., 20, 177- 184. , D.A. Menzies, and C.R. Booth, 1997: Oceanographic Bio- Optical Profiling System II, Ocean Optics XIII, S.G. Ackelson and R. Prouin, Eds., Proc. SPIE, 2963, 777-789. Wangl M., 2000: "The SeaWiFS atmospheric correction algorithm updates." In: McClain, C.R., E.J. Ainsworth, R.A. Barnes, R.E. Eplee, Jr., F.S. Patt, W.D. Robinson, M. Wang, and S.W. Bailey, SeaWil$ Postlaunch Calibration and Validation Analyses, Part 1. NASA Tech. Memo. 2000-206892, Vol. 9, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 57-63. Zibordi, G., and G.M. Ferrari, 1995: Instrument self-shading in underwater optical measurements: experimental data, Appl. Opt., 34, 2,750-2,754. _, J.P. Doyle, and S.B. Hooker, 1999: Offshore tower shading effects on in-water optical measurements. J. Atmos. Ocean. Technol., 16, 1,767-1,779. THE SEAW1FS POSTLAUNCH TECHNICAL REPORT SERIES Vol. I Johnson, B.C., J.B. Fowler, and C.L. Cromer, 1998: The Seatember 1994. NASA Tech. Memo. 104566, Vol. 3J, S.B. WiFS Transfer Radiometer (SXR). NASA Tech. Memo. Hooker, E.R. Firestone, and J.G. Acker, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 78 pp. 48 1998-206892, Vol. 1, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 58 pp.

Original page 55

O'Reillyetal. Vol. 2 Aiken, J., D.G. Cummings, S.W. Gibb, N.W. Rees, R. Woodd- Walker, E.M.S. Woodward, J. Woolfenden, S.B. Hooker, J-F. Berthon, C.D. Dempsey, D.J. Suggett, P. Wood, C. Donlon, N. Gonz_lez-Ben_tez, I. Huskin, M. Quevedo, R. Barciela-Fernandez, C. de Vargas, and C. McKee, 1998: AMT-5 Cruise Report. NASA Tech. Memo. 1998-206892, Vol. 2, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, l l3pp. Vol. 3 Hooker, S.B., G. Zibordi, G. Lazin, and S. McLean, 1999: The SeaBOARR-98 Field Campaign. NASA Tech. Memo. 1999-206892, Vol. 3, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 40 pp. Vol. 4 Johnson, B.C., E.A. Early, R.E. Eplee, Jr., R.A. Barnes, and R.T. Caffrey, 1999: The 1997 Prelaunch Radiometric Calibration of SeaWiFS. NASA Tech. Memo. 1999-206892, Vol. 4, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 51 pp. Vol. 5 Barnes, R.A., R.E. Eplee, Jr., S.F. Biggar, K.J. Thome, E.F. Zalewski, P.N. Slater, and A.W. Holmes 1999: The Sea- WiFS Solar Radiation-Based Calibration and the Transferto-Orbit Experiment. NASA Tech. Memo. 1999-206892, Vol. 5, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, 28 pp. Vol. 6. Firestone, E.R., and S.B. Hooker, 2000: SeaWiFS Postlannch Technical Report Series Cumulative Index: Volumes 1-5. NASA Tech. Memo. 2000-206892, Vol. 6, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 14 pp. Vol. 7 Johnson, B.C., H.W. Yoon, S.S. Bruce, P-S. Shaw, A. Thompson, S.B. Hooker, R.E. Eplee, Jr., R.A. Barnes, S. Maritorena, and J.L. Mueller, 1999: The Fifth SeaWiFS Intercalibration Round-Robin Experiment (SIRREX-5), July 1996. NASA Tech. Memo. 1999-_06892, Vol. 7, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, 75 pp. Vol. 8 Hooker, S.B., and G. Lazin, 2000: The SeaBOARR-99 Field Campaign. NASA Tech. Memo. 2000-206892, Vol. 8, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, 46 pp. Vol. 9 McClain, C.R., E.J. Ainsworth, R.A. Barnes, R.E. Eplee, Jr., F.S. Patt, W.D. Robinson, M. Wang, and S.W. Bailey, 2000: SeaWiFS Postlaunch Calibration and Validation Analyses, Part 1. NASA Tech. Memo. 2000-206892, Vol. 9, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, 82 pp. Vol. 10 McClain, C.R., R.A. Barnes, R.E. Eplee, Jr., B.A. Franz, N.C. Hsu, F.S. Patt, C.M. Pietras, W.D. Robinson, B.D. Schieber, G.M. Schmidt, M. Wang, S.W. Bailey, and P.J. Werdell, 2000: SeaWiFS Postlaunch Calibration and Validation Analyses, Part 2. NASA Tech. Memo. 2000-206892, Vol. 10, S.B. Hooker and E.R. Firestone, Eels., NASA Goddard Space Flight Center, 57 pp. Vol. 11 O'Reilly, J.E., and 24 Coauthors, 2000: SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3. NASA Tech. Memo. 2000-206892, Vol. 11, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, 49 pp. 49

Original page 56

Original page 57

Original page 58

REPORT DOCUMENTATION FormApproved PAGE OMBNo. 0704-0188 Public reporting burden k_" this collection of information Is estimated to ave_age 1 hour per response, including the time for reviewing Instructions, searching existing data sources, gathering and maintaining the data needed, and completing and revk_ the collection of information. Send comments regarding this burden estimate or any other aspect of this oo_ctlon of information, Including suggestk)ns for reducing this burden, to Washington Headquarters Services, Directorate for Information Operatk)ns and Repofls, 1215 Jefferson Davis Highway, Suite 1204. A_ln_on TVA 2220_-4302_ and to the Office of Mans_lernent and Budget, P<,pem_rk Reduction Project pT04-01Se I, Washin_on, DC 20503. 1. AGENCYUSE ONLY (Leaveblank) 2. REPORTDATE October 2000 4. TITLEAND SUBTITLE SeaWiFS Postlaunch Technical Report Series Validation Analyses, Part 3 Code 970.2 Volume 11: SeaWiFS Postlaunch Calibration and 3. REPORTTYPE AND DATESCOVERED Technical Memorandum 5. FUNDINGNUMBERS 6. AUTHORS) J.E. O'Reilly, S. Maritorena, M.C. O'Brien, D.A. Siegel, D. Toole, D. Menzies, R.C. Smith, J.L Mueller, B.G. Mitchell, M. Kahru, R.P. Chavez, P. Strutton, G.F. Cota, S.B. Hooker, C.R. McClain, K.L. Carder, F. Muller-Karger, L. Harding, A. Magnuson, D. Phinney, G.F. Moore, J. Aiken, K.R. Arrigo, R. Letelier, and M. Culver Series Editors: Stanford B. Hooker and Elaine R. Firestone 7. PERFORMINGORGANIZATIONNAME(S)AND ADDRESSES) Laboratory for Hydrospheric Processes Goddard Space Flight Center Greenbelt, Maryland 20771 • ,l,w 8. PERFORMINGORGANIZATION REPORTNUMBER 2001-00416-0 ........ AGENCYNAME(S)ANDADDRESS(ES) 10. SPONSORING/MONITORING 9. SPONSORING/MONITORING National Aeronautics and Space Administration Washington, D.C. 20546-0001 11. SUPPLEMENTARYNOTES See Title Page for author affiliations. 12a. DISTRIBUTION/AVAILABIMTYSTATEMENT Unclassified-Unlimited Subject Category 48 AGENCYREPORTNUMBER TM--20(0)-206892, Vol. 11 12b. DISTRIBUTIONCODE Report is available from the Center for AeroSpace Information (CASI), 7121 Standard Drive, Hanover, MD 21076-1320; (301)621-0390 13. ABSTRACT (urn200 won) Volume 11 continues the sequential presentation of postlaunch data analysis and algorithm descriptions begun in Volume 9. Chapters 1 and 2 present the OC2 (version 2) and OC4 (version 4) chlorophyll a algorithms used in the SeaWiFS data second and third reprocessings, August 1998 and May 2000, respectively. Chapter 3 describes a revision of the K(490) algorithm designed to use water-leaving radiances at 490 nm which was implemented for the third reprocessing. Finally, Chapter 4 is an analysis of in situ radiometer calibration data over several years at the University of California, Santa Barbara (UCSB) to establish the temporal consistency of their in-water optical measurements. 14. SUBJECTTERMS Chlorophyll a Algorithm, OC2, 49 SeaWiFS, Oceanography, Calibration, Validation, 15. NUMBER OF PAGES OC4, K(490), Diffuse Attenuation Coefficient, Marine Environmental Radiometer, 16. PRICE CODE MER 17. SECURITYCLASSIFICATION 18.SECURITYCLASSIFICATION 19.SECURITYCLASSIRCATION OF REPORT OF THISPAGE Unclassified Unclassified NSN 754_01-280-5500 OF ABSTRACT Unclassified 20. UMITATIONOF ABSTRACT Unlimited Standard For,_ 298 (Rev. 2-89)