Full report

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• / NASA Technical Memorandum 104566, Vol. 22 9 SeaWiFS Technical Report Series Stanford B. Hooker, Elaine R. Firestone, and James G. Acker, Editors Volume 22, Prelaunch Acceptance Report for the SeaWiFS Radiometer Robert A. Barnes, William L. Barnes, Wayne E. Esaias, and Charles R. McClain SEPTEMBER 1994 (NASA-TM-lO4566-Vol-22) SeaWiFS N95-32672 TECNNTCAL RFPCRT SERIES. VCLU_E 22: PPELAUNCH ACCEPTANCE REPORT FOR THE SeaWfS RAOIOMETER (NASA. Goddard Unclas Space Flight Center) 36 p G3/48 0062508

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NASA Technical Memorandum 104566, Vol. 22 SeaWiFS Technical Report Series Stanford B. Hooker, Editor NASA Goddard Space Flight Center Greenbelt, Maryland Elaine R. Firestone, Technical Editor General Sciences Corporation Laurel, Maryland James G. Acker, Technical Editor Hughes STX Lanham, Maryland Volume 22, Prelaunch Acceptance Report for the SeaWiFS Radiometer Robert A. Barnes Man Tech, Inc. Wallops Island, Virginia William L. Barnes Wayne E. Esaias Charles R. McClain NASA Goddard Space Flight Center Greenbelt, Maryland National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 1994

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This publication is available from the NASA Center for AeroSpace Information, 800 Elkridge Landing Road, Linthicum Heights, MD 21090-2934, (301) 621-0390.

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain ABSTRACT The final acceptance, or rejection, of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) will be determined by the instrument's on-orbit operation. There is, however, an extensive set of laboratory measurements describing the operating characteristics of the radiometer. Many of the requirements in the Ocean Color Data Mission (OCDM) specifications can be checked only by laboratory measurements. Here, the calibration review panel (composed of the authors of this technical memorandum) examines the laboratory characterization and calibration of SeaWiFS in the light of the OCDM performance specifications. Overall, the performance of the SeaWiFS instrument meets or exceeds the requirements of the OCDM Contract in all but a few unimportant details. The detailed results of this examination are presented here by following the outline of the specifications, as found in the Contract. The results are presented in the form of requirement and compliance pairs. These results give conclusions on many, but not all, of the performance specifications. The acceptance by this panel of the performance of SeaWiFS must only be considered as an intermediate conclusion. The ultimate acceptance (or rejection) of the SeaWiFS data set will rely on the measurements made by the instrument on orbit. I. INTRODUCTION In additionto itsroleas an ocean colorexperiment,the to the OCDM performance specifications is the responsibility of OSC. The contract between OSC and SBRC has incorporated the OCDM performance specifications almost Sea-viewing Wide Field-of-viewSensor (SeaWiFS) serves completely. There have been a few instances in which the as a satellite procurement experiment for the National Aeronautics and Space Administration (NASA). For the SeaWiFS Project, NASA is procuring data, not an instrument designed by the agency. NASA has entered into a contractual agreement, the Ocean Color Data Mission (OCDM) contract, (hereinafter referred to as the Contract, unless otherwise stated) with Orbital Sciences Corporation (OSC) to obtain, at a fixed price, an ocean color data set. OSC has, in turn, entered into an agreement with the Hughes Santa Barbara Research Center (SBRC) for which SBRC, as a subcontractor, has built the satellite sensor required to provide these data. In this arrangement, SBRC has had the freedom to design an instrument which meets the predetermined set of specifications. The design of the testing procedures for the instrument has also been left to SBRC. Although not written in the specifications, it is the responsibility of the Project to understand the design, the operation, and the calibration of the satellite sensor. The Project also has the responsibility of transferring this understanding to the community of scientists who will use the ocean color data set. Without a specific requirement in the Contract, SBRC, OSC, and the Project set up an unofficial program of visits to the instrument builder by a Project deliverables in the subcontract between OSC and SBRC have not provided the information needed by the Project to assure compliance with the OCDM specifications. In those instances, the informal arrangement has given a mechanism for the Project to obtain the necessary information. The major events in the construction and testing of the SeaWiFS instrument are given in Table 1. Throughout this period, the Project has worked as an active partner with SBRC. This partnership has been of great advantage to the Project. The Project representative has been given access to all of the technical information about SeaWiFS, plus access to the engineers and technicians working on the instrument. Technical problems that arose during construction were openly discussed by SBRC and the Project. In addition, test procedures were developed, in part, through informal talks between SBRC engineers and the Project representative. The representative was an active participant in several of the tests. Again, this active participation has been of great advantage to the Project. In this review of the SeaWiFS specifications, the review panel can base its conclusions on a set of tests and calibrations with results and procedures that the panel understands. More importantly, the active participation has provided a greater understanding of representative during the construction and calibration of the operation of SeaWiFS. This includes an understand- SeaWiFS. From the outset, these visits developed into a ing of some of the characteristics that are particular to collaboration between SBRC and the Project, rather than strict supervision by NASA, over the instrument development. This arrangement has been non-standard in another way, since the Contract remains an agreement between NASA and OSC. Care has been taken to ensure no interference from the Project in the contractual obligations between OSC and SBRC. It should be noted that adherence the instrument---characteristics that the SBRC engineers have called its personality. These include the instrument's along-track modulation transfer function (MTF), discussed below, and its stray light characteristics, which will be discussed at length in a future volume within the SeaWiFS Technical Report Series. Such understanding will be crucial as the Project works to interpret the data that the radiometer will transmit from orbit.

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PrelaunchAcceptanceReportfor the SeaWiFS Radiometer 2_able 1. Major events in the construction and testing of the SeaWiFS instrument. Date Noteworthy Event 16 May 1991 Letter Contract Signed between OSC and SBRC 6 July 1991 Preliminary Design Review 16 December 1991 Critical Design Review 16 September 1992 Engineering Design Unit Completed 27 October 1992 SBRC and GSFCt Integrating Sphere Comparison 8 December 1992 First Field Test (lunar and solar measurements) 15 January 1993 Vibration and Thermal-vacuum Testing 7 March 1993 Second Field Test 27 April 1993 Initial Pre-Ship Review 27 May 1993 Stray Light Paths Review (at GSFC) 3 August 1993 Performance Specification Modification (at OSC) 26 October 1993 Vibration Testing of Modification Workmanship 1 November 1993 Third Field Test 22 November 1993 Completion of Instrument 2 December 1993 Post-Modification Pre-Ship Review Goddard SpaceFlightCenter It is the opinion of the review group that in light of the instrument design and testing program, the prelaunch performance of the SeaWiFS radiometer meets, or exceeds, the requirements of the Contract in all but a few small deit leftto right.In the same manner, the along-trackvalues tails, which are considered to be minor. In addition, is the opinion of the review group that the testing of the instrument has also been adequate to allow these conclusions. The along-scan and along-tracklinespread functions for the e_ght SeaWiFS bands are shown in Fig. i. The along-scanvaluesare given in the directionofscan, i.e.,the values are representativeof the instrument scanning from are given in the directionof flight,i.e,for an instrument moving leftto right.For the purposes ofFig. 1,the offsets have been removed from the data, and the data have been individualparts of the per- normalized to unity. As shown in Fig. I, the right-most In Sections 2 through 22, sec- data points in both scans have been setto zero. The scans formance specificationsare addressed. Some of these thatdo not involvethe radiome- in Fig. 1 alsoprovide the basis for the MTF calculations tionsincluderequirements ter_sperformance. One such sectionis Section 20, which and forthe band-to-band registrationcalculations. require- The basic method for determining the field-of-viewis concerns satellitepointing data. These additional those to calculatethe full-widthat half-maximum (FWHM) for ments are discussedin the compliance section for of the the along-scan and along-trackmeasurements. These respecifications.Section 23 gives a short summary conclusions. 2. FIELD-OF-VIEW 2.1 Requirement The instantaneous field-of-view (IFOV) at nadir and 0 ° tilt shall be between 1 and 1.21 kin. Sampling shall be done once per nominal (square) IFOV. 2.2 Compliance The field-of-view of the instrument is determined from data measured by scanning a narrow slit across the nadir sultsare presentedin Table 2. In addition,the resultsare presented in terms of the length of an arc that subtends the angle at a distanceof 705 kin. Such an arc represents the width of the footprintof the SeaWiFS measurement, assuming that the instrument is705 kln above the Earth. The valuescalculatedhere are in agreement with the calculationsfound in the SeaWiFS Calibrationand Acceptance Data Package (SCADP). The SCADP was generated by A. Holmes of SBRC inthe course of constructing,calibrating, and testingthe SeaWiFS instrument. Many of the conclusions made by the review panel are based on information found in the SCADP. However, these calculationsdo not adequately represent the two-dimensionai nature of the field-of-view.The pixel, both along-scan and along-track. The narrow slit is shape of a SeaWiFS footprintis not a perfectrectangle, 0.16 mrad wide (about 0.1 of the width of a pixel), and the sincethe linespread functionsarenot perfectsquare waves. slitisscanned in 0.1mrad increments. The slitoverfillsthe To betterrepresentthe SeaWiFS footprint,the along-scan narrow opening. and along-trackvalues foreach band have been combined pixelin the directionperpendicularto its is intotwo-dimensional arrays.Each element in the array is The term forthe resultsfrom thistype of measurement a line spread function. 2 the product of the value at the ordinate (the along-scan

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain 1.0 0.9 0.8 0.7 0.S 0.3 0.2 0.1 0.0 1 2 3 4 -0.1 Increment Immdl 1.0 0.9 0.8 0.7 0.6 j 0.5 _ 0.4 t 0.3 0.2 0.1 0.0 I 2 3 4 -0.1 Increment (ndlt_ll -- BAND I ........ BAND 2 ................ BAND 3 ............ BAND 4 .......... BAND 5 BAND 6 ........ BAND 7 ............... BAND 8 5 6 7 10 -- BAND 1 ........ BAND2 ................ BAND 3 ......... BAND 4 .......... BAND 5 -- BAND 6 ........ BAND 7 ...................BAND 8 5 6 7 8 9 10 Fig. 1. The along-scan and along-track line spread functions. The top figure shows the along-scan line spread function. In this figure, the zero offsets have been removed from the data, and the results have been scaled to unity. The bottom figure shows the along-track line spread function. As in the top figure, the zero offsets have been removed from the data, and the results have been scaled to unity. 3

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Prelaunch Acceptance Report for the SeaWiFS Radiometer Table 2. Field-of-view calculations. All measurements Along-Scan Values given are the FWHM of the line spread function. Along-T_ack Values Band These Results SCADP These Results SCADP No. [mrad] [kin] [mrad] 1 1.84 1.30 2 1.78 1.26 3 1.82 1.28 4 1.78 1.25 5 1.82 1.28 6 1.80 1.27 7 1.76 1.24 8 1.77 1.2 Mean 1.80 1.27 1.8 Std. Dev. 0.03 0.02 relative response) and the value of the abscissa (the alongtrack relative response). This result can be represented a three-dimensional figure (Fig. 2), with the base given as the Global area coverage (GAC) data subsampled from the the ordinate and abscissa locations, and the height product of the ordinate and abscissa values. instru- than 5=45° • Figure 3 shows the 50% cross section of the ment response for band 7. It gives the edge of the thre_ dimensional figure at the half maximum of the response for the band in Fig. 2. Figure 3 also shows the values for the major axes, i.e., for the axis with an along-scan value of unity and for the axis with an along-track value of unity. distance 1 2.67 1.64 1.15 Each of the two axes gives the widest possible [km] [mrad] [km] [mrad] [kin] 1.70 1.20 1.69 1.19 1.68 1.19 1.70 1.20 1.69 1.19 1.67 1.18 1.66 1.17 1.65 1.16 1.27 1.68 1.18 1.7 1.20 0.02 0.01 than 1500 km for tilts of ±20 ° to enable two-day global as coverage from the nominal altitude. All scan data shall be as transmitted in the local area coverage (LAC) broadcast. cross-track scan need not include data taken at greater Table 3. Field-of-view, calculated from the footprint area• Band Cross- Side Side No. Sectiont Length $ Length § across the cross section in each direction. When these 2 2.51 1.58 1.12 give 3 2.55 1.60 1.12 widest possible distances are multiplied together, they an area that is larger than the actual footprint in Fig. 3. added 5 2.73 1.65 1.16 Figure 4 shows the 50% cross section without the roughly, 6 2•48 1.57 1.11 axes. This footprint for band 7 is nominally, i.e., 4 2.44 1.56 1.10 preferable 7 2.53 1.59 1.12 square. For the purposes of this review, it seems to define the field-of-view of the SeaWiFS measurements in 8 2.50 1.58 1.11 terms of the area of the (nominally) square footprint. For Mean 1.60 1.13 the eight SeaWiFS bands, the area within the 50% cross Std. Dev. 0.03 0•02 sections was calculated, and the length for the side of a square that would enclose those areas was subsequently determined. Table 3 gives the results of the calculations. The lengths of the sides in Table 3 then give the best repmrad 2 _mrad §kin 3.2 Compliance resentation of the fields-of-view of the eight bands in the The angular portion of the SeaWiFS measurements instrument, as determined by this review. is determined by the rotation rate of the optics within The average side length for SeaWiFS is 1.60 mrad, or the instrument, the sampling frequency of the instrument, 1.13 km, at an altitude of 705 kin. The actual values range and the number of samples in a scan line. The optics from 1.10-1.16 km. All values conform to the requirement within the SeaWiFS instrument rotate 6 times per secof the specifications for an IFOV between 1 and 1.21 kin. ond 6×360 ° s-l). The time period between pixels is 42ps. 3. CROSS-TRACK SCAN 3.1 Requirement The active portion of the cross-track scan shall not be 116.6 ° The specifications call for this angle to be between 90 ° less than 90 ° (±45 ° about nadir) nor greater than (+58.3 ° about nadir). The swath width shall not be less 4 There are 1,285 pixels per scan line. The calculation is shown in (1): 6 × 360°s -1 42 x 10-6s 1,285pixels 116.58 ° • pixel scanline ---- scanline" (1) and 116.6 ° . It should be noted that the distance from the

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R.A.Barnes,W.L.Barnes,W.E.Esaias,andC.R.McClain Fig. 2. Theresponse(field-of-view)forSeaWiFSband7 in threedimensions.Theaxesforthebaseare in the along-scanandalong-trackdirections.Theheightshowstheresponseofthe bandnormalizedto unity.

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Prelaunch Acceptance Report for the SeaWiFS Radiometer 35 * 3O .lal 25 2O 15 151 .Sil 10 , i i i ] I i I ' I , , , * l , = , , J , , , ¢ t 4.5 50 55 60 65 7C Along Soon [0.1mRod,/tk:k] Fig. 3. The cross section of the response of SeaWiFS band 7 at the 50% response level. The two axes within the cross section correspond to the FWHM values in Table 1. The 1:1 point marks the maximum response for the band. The other four points are located on the half maximum contour. 35 ' ' ' ' I ' 3O m =I 25 o_ E '- ZO [ 15 J 10 I , , , I , , , , I , , , , ¢ , , J .... 45 50 55 6O 55 7C NOng Soon [0.tmRad/tJck] Fig. 4. The measurement footprint for SeaWiFS band 7. The best estimate of the field-of-view for this band is calculated as the side of a square with an area equal to this footprint.

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R.A.Barnes,W.L. Barnes,W.E.Esaias,and C.R. McClain start to the end of the first pixel is one pixel. Thus, the distance from the start of the first pixel to the end of the 1,285th pixel is 1,285 pixels. The distance from the center of the first pixel to the center of the 1,285th pixel is 1,284 angles include the optical paths through the instrument. Thus, the values in Table 4 include measurements with both sides of the half angle mirror. All of the values in this table are given with respect to the alignment mirrors. The pixels. As a result, the angular distance from the center of SCADP gives the uncertainty for the aft tilt as +0.003 °, pixel 1 to the center of pixel 1,284 is 116.48 °. A figure in the SCADP gives a clock rate of 1.905 MHz +1%. It also shows that there are 80 bits per pixel, or 41.99 microseconds (+1%) per pixel. The rotation rate and the number of pixels per scan line are also described in the SCADP. Subsampling of each scan line for GAC will be performed by the SeaStar bus. This subsampling will give the 90 ° angular range (centered about nadir), which is required in the specification. 4. FORE-AND-AFT POINTING 4.1 Requirement The data shall be taken with a sensor capable of pointing the swath fore and aft (positive and negative with respect to the velocity vector, respectively) to avoid specular solar reflectance from the ocean's surface. The sensor scan must be capable of tilts of 0.0 °, +20.0 °, and -20.0 ° from nadir. Changes in the tilt angle from -20 ° to +20 ° shall take less than 30 seconds. Data describing the tilt angle shall be accurate to within 0.01% 4.2 Compliance The nadir direction for SeaWiFS is given as the +x axis. The instrument scans in the (x,z) plane, and the solar diffuser points in the +y direction. The diffuser points at the sun after the instrument has completed its Earth views and is passing over the South Pole. The diffuser is at the back of the instrument. SeaWiFS flies in the -y direction. A forward tilt has a -y direction and a backward tilt has a +y direction; the values here are from the SCADP. The fore and aft angles have been measured relative to nadir. The angles for nadir direction were measured with respect to the alignment mirrors mounted on the instrument. Here is a brief description of the procedure that was used to measure the fore and aft tilt angles relative to nadir. With the instrument at zero tilt, a collimated light source was aligned with pixel 643 of the SeaWiFS scan. The entire instrument was then rotated in a specially designed cradle fore and aft 20 °, and the scanner was tilted in the other direction. The cradle was designed to rotate the instrument to these 20 ° locations with great accuracy. The instrument tilt realigned the nadir pixel of the instrument with the collimated light source. The collimated light source was moved in the y direction to determine the difference in the tilt angle from 20 ° . Since the tilt angles used in this procedure were determined by SeaWiFS measurements of the source, these and for the nadir and forward tilt the error is given as +0.006% The specifications call for tilt knowledge to be within 0.01% The SeaWiFS scanner tilts from -20 to +20 ° in about 13 seconds. The speed profile for the tilt is Gaussian, with a maximum speed of about 6 ° s-1. • hble 4. SeaWiFS tilt angles. Tilt Mirror Side Ang/e Uncertainty Aft A 19.896 ° ±0.003 ° Aft B 19.888 ° +0.003 ° Aft Average 19.892 ° ±0.003 ° Nadir A 0.075 ° :t:0.006 ° Nadir B 0.068 ° :i:0.006 ° Nadir Average 0.072 ° :t:0.006 ° Fore A -19.850 ° +0.006 ° Fore B -19.857 ° +0.006 ° Fore Average -19.853 ° +0.006 ° 5. DARK LEVEL 5.1 Requirement A portion of every scan shall contain sensor output data while the field-of-view is obscured and the input radiance is less than the Noise Equivalent Differential Spectral Radiance (NEdL). 5.2 Compliance The SeaWiFS instrument incorporates a zero offset, or dark restore value, for each scan of the instrument. This value is provided in accordance with the dark level measurements specification. For details on the design and positioning of the dark restore, the reader is referred to Fig. 1 of Woodward et al. (1993), which shows dark direct current (DC) restore at the angular range between 140 ° and 220° from nadir for each SeaWiFS scan. SeaWiFS provides the dark level measurements required by the specifications. 6. BAND TOLERANCES 6.1 Requirement The location of the band edges shall be ±2 nm (3 a) of the values in Table 1, and shall be stable to less than ±1 nm over the duration of the ground test program. The edge range shall not exceed 50% of the bandwidth in any spectral band. 7

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Reportfor the SeaWiFS Radiometer PrelaunchAcceptance 6.2 Compliance 6.2.1 Band Edges The band edge calculations are described in Barnes et al. (1994). The results presented here have been taken from that manuscript, and are summarized in Tables 5-7. These tables include the 5%, 50%, and 80% response levels that are required to calculate the band edges and the edge ranges. The specifications call for the band edges to be within +2 nm of the values in the specifications. The right (upper) band edge for band 8 falls at the 2.0nm limit, and the remaining band edges are within the specification limits. The band edge and edge range results in Barnes et al. (1994) are in agreement with the results in found in the SCADP. 6.2.2 Edge Ranges The specifications require that the edge range for each band shall not exceed 50% of the bandwidth. The edge range is the wavelength interval between 5% of peak response and 80% of peak response. The edge range values are given in Tables 6 and 7. These values were also taken from the calculated results in Barnes et al. (1994). The edge range for band 2, left edge, is 54% of the bandwidth. The edge range for band 6, right edge, is 51%. The remaining ratios fall within the 50% limits. 7. OUT-OF-BAND RESPONSE 7.1 Requirement The out-of-band response shall be less that 5% of the within-band value. Each 1% point shall be within 1.5 times the bandpass from the corresponding band edge. Compliance with this specification shall be determined for a source with spectral shape equivalent to L¢loud (the spectral radiance of a Lambertian surface of 100% reflectance illuminated by the sun at 22.5 ° zenith angle). Note: The Lc|oud radiances can be found in Table 18, below. They are also called the SeaWiFS maximum cloud radiances. 7'.2 Compliance 7.2.1 Out-of-Band Response. The in-band response is defined as the integrated response of each band between the 1% transmission points. The out-of-band response is defined as the integrated response at all other wavelengths. The ratio of out-of-band response to in-band response is used to give the percent out-of-band response. These values have been calculated by Barnes et al. (1994). Tables 8 and 9 have been adapted from Table 12 of Barnes et al. (1994) and are based on measurements using a 5,900K blackbody source, as required in the specifications. A 5,900 K blackbody duplicates the spectral shape of the solar output over the wavelength range of the SeaWiFS measurements (Barnes et al. 8 1994). All of the calculated out-of-band values are well within the specifications. Table 9 contains a compar_ from Barnes et al. (1994) with those frog ectral data provided as part of the SCAD ff calculations show reasonable agreement 7.2.2 : Point The spq that each 1% response point shall be wi le bandwidth from the corresponding b :alculated results are given in Tables 10 Its are also derived from calculations in B :). The calculations have been made using dy source, in accordance with the specific ; 1% response points are well within the s S. In generl the SeaWiFS bands are a significant imp: shapes required by the specifications. 8. SPEC FERENCES 8.1 Requ, If multipl nts are used within a band, the spectral letector elements in a band shall be com ion and shape, by use of norrealized speci yes. The central wavelength of any elemen +0.5 nm of the average central waveleng _ts of the band. The integrated spectrl rn the 10% response points shall not dige .0% for any two elements in the band. 8.2 Compl 8.2.1 Cet ........... ,,gth No spectral measurements have been specifically designed for the SeaWiFS instrument to confirm this specification. However, there is evidence to indicate that the central wavelength for each of the four channels in each SeaWiFS band is well within 0.5 nm of the average central wavelength for that band, as called for in the specifications. The design of SeaWiFS has the four channels for each band located below a single interference filter for that band. As shown in Barnes et al. (1994), the shape of the spectral response of the filter dominates the determination of the central wavelength. Barnes et al. (1994) also shows that the quantum efficiency of the type of silicon photodiode used in SeaWiFS is roughly constant over the 10-20 nm half-widths of the interference filters. This spectral flatness implies a very minor effect from the detectors on the central wavelength of the band.

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain Table 5. Reference wavelengths for band edge and edge range calculations. All measurements are in nanometers. Band Left Right No. 5% Point 50% Point 80% Point 80% Point 50% Point 5% Point 398.4 403.2 407.4 427.8 434.1 438.3 474.6 480.8 483.3 492.8 498.9 501.1 540.4 545.5 547.6 653.4 658.3 660.1 734.5 744.7 748.9 835.8 845.7 849.2 421.1 423.4 428.9 451.0 453.7 459.5 499.4 501.4 507.1 518.9 521.2 527.2 561.4 563.8 570.4 675.6 678.2 685.8 780.8 785.0 798.3 884.1 887.0 896.8 Table 6. Band edge calculations. All measurements and calculated quantities are in units of nanometers. Band Left Band Edge Resu/ts No. Specified Measured Difference 402 403.2 1.2 433 434.1 1.1 480 480.8 0.8 500 498.9 -1.1 545 545.5 0.5 660 658.3 -1.7 745 744.7 -0.3 845 845.7 0.7 Right Band Edge Results Specified Measured Difference 422 423.4 1.4 453 453.7 0:7 500 501.4 1.4 520 521.3 1.3 565 563.8 -1.2 680 678.2 -1.8 785 785.0 0.0 885 887.0 2.0 Table 7. Edge range calculations. All measurements are in nanometers. Band Bandwidth Left Edge Percent of Right Edge Percent of No. Range Bandwidth Range Bandwidth 1 20.2 9.0 2 19.6 10.5 3 20.6 8.7 4 22.4 8.3 5 18.3 7.2 6 19.9 6.7 7 40.3 14.4 8 41.3 13.4 45 7.8 39 54 8.5 43 42 7.7 37 37 8.3 37 39 9.0 49 34 10.2 51 36 17.5 43 32 12.7 31

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PrelaunchAcceptanceReportforthe SeaWiFSRadiometer Table 8. Calculated out-of-band responses for the eight SeaWiFS bands. The instrument responses are given as the output of the photodiode in picoamperes (pA). The 5,900 K radiances in the calculations are normalized to the expected saturation radiance for each band at the nominal center wavelength for each band. The upper and lower extended band edges come from Tables 7 and 8 of Barnes et al. (1994). These results are calculated over the wavelength range from 380-1,150 nm. Lower In-Band Upper Upper Out-of-Band Lower Band Out-of-Band Response Extended Out-of-Band Response Extended No. Response [pA] [pA] Band Edge [nm] Response [pA] [%] Band Edge [nm] 1 3.38 395.2 2175.34 433.6 11.77 0.70 2 9.59 424.1 3418.80 463.7 1.56 0.33 3 6.48 470.7 4301.14 511.7 28.08 0.80 488.1 4586.23 530.7 8.96 0.58 4 17.32 536.3 3631.84 577.2 46.14 2.35 5 39.14 6 12.66 2071.19 692.5 7.84 0.99 646.7 7 10.17 2818.97 813.4 29.58 1.41 727.3 8 66.36 2191.97 907.5 15.43 3.73 826.4 Thble 9. A comparison of the calculated instrument out-of-band response results found in Barnes et al. (1994) with SCADP results for the same parameter. Both sets of calculations show the instrument's out-of-band response to be within the 5% value in the specifications. Band Barnes et al. (1994) SCADP No [%] [%] 1 0.70 0.65 2 0.33 0.40 3 0.80 0.80 4 0.58 0.57 5 2.35 2.35 6 0.99 0.98 7 1.41 1.41 8 3.73 3.73 The detectors in each band are etched from a single of four 9. BAND CO-REGISTRATION piece of silicon. The overall dimensions for the set detectors are approximately 0.05in x 0.01 in. Assuming 10%, i.e., the range from greatest to least integrated response for the elements can be no more than 10% of the value of the average integrated response. Measurements of individual SeaWiFS channels with the SBRC integrating sphere have shown that the output from the individual detectors in each band corresponds at the 1% level. That is, the integrated response of the detectors agrees at the 1% level. Of course, the output from each channel has been adjusted (or rather, the values of the resistors in the operational amplifiers have been adjusted) to give uniformity at the 1% level. In general, switching from detector to detector in a SeaWiFS band will give a change in output from the instrument on the order of l_'_-considerably better than the 10% limit in the specification. This 10% specification was included in the SeaWiFS specification, in case the design of the flight instrument included area arrays with many individual detectors. reasonable uniformity in the manufacture of the silicon ma- 9.1 Requirement terial, the four detectors in each band should have nearly identical spectral response over the half-width of the interference filter. It is the response of the interference filter, not the detectors, that dominates the determination of the central wavelength for each SeaWiFS band. The estimate The IFOVs from all spectral bands shall be co-registered to within 0.3 pixel (1 a). 9.2 Compliance primarily The specification requires that the IFOVs from all specof the within-band spectral differences is based of the tral bands be co-registered within 0.3 pixel. From the fieldon an assumption of uniformity in the manufacture interference filter. This estimate of uniformity covers an area of 0.05 in x 0.01 in. 8.2.2 Integrated Spectral Response of-view calculations in Section 2 above, it was determined that the IFOV for the instrument is 1.6 mrad on a side. The band-to-band registration results presented here are based on the along-scan and along-track line spread functions in Section 2. The line spread measurements were The within-band spectral response specification also re- made by moving a narrow slit across the field-of-view of 10% the nadir SeaWiFS pixel. The slit was part of a colliquires an integrated spectral response, between the within mated light source, and the slit was moved in increments response points for the individual elements, to be 10

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R.A.Barnes,W.L.Barnes,W.E.Esaias,andC.R.McClain Table 10. Reference wavelengths for one percent response point calculations. All values are in nanometers. Band Left No. 1% Point 50% Point 1 395.2 403.4 2 424.1 434.2 3 470.7 480.8 4 488.1 498.9 5 536.3 545.4 6 646.7 658.3 7 727.3 744.4 8 826.4 845.5 Center Right Wavelength 50% Point 1% Point 413.4 423.4 433.6 444.0 453.8 463.7 491.1 501.4 511.7 510.1 521.3 530.7 554.6 563.8 577.2 668.2 678.1 692.5 764.6 784.9 813.4 866.1 886.7 907.5 Table 11. One percent response point calculations. The specifications call for a ratio to the bandwidth that is less than 150%. The bandwidths were previously given in Table 7. Band Bandwidth Left 1% from Percent of Right 1% from Percent of No. [nm] Left 50% Into] Bandwidth Right 50% [nm] Bandwidth 20.0 8.2 19.6 10.1 20.6 10.1 22.4 10.8 18.4 9.1 19.8 11.6 40.5 17.1 41.2 20.1 (ticks) equal to a 0.1 mrad angular displacement as seen by the instrument. The center for each pixel (in ticks) was calculated as the average of the positions of the two half maximum points for each band. The along-scan and alongtrack centers were calculated independently. The absolute values for the central positions (in ticks) are not important in these results--it is the relative locations of the central points that are relevant here. Table 12 gives the alongscan results. Table 13 gives the along-track results. Figure 5 shows the results relative to the average for the set of band centers, and also shows the locations of the eight band centers in two dimensions. Figure 5 also includes a square 0.1 pixel wide, centered on the average band center. The maximum distance between band centers in the along-scan direction is 0.15 pixels, and the maximum distance along-track is 0.21 pixels. The instrument's spectral band-to-band registration is significantly better than the requirements of the specifications. 10. SENSITIVITY 10.1 Requirement Table 14 provides the signal-to-noise ratio (SNR) specifications for all bands at a gain value of unity. The required SNR shall be achieved at the typical spectral radiance levels (/typical). NEdL may be calculated from the expression: NEdL= Ltypical/SNR. 41 10.2 51 52 9.9 50 49 10.3 50 48 9.4 42 50 13.4 73 59 14.4 73 42 28.5 70 49 20.8 50 10.2 Compliance The noise in the SeaWiFS instrument was measured by viewing the SBRC integrating sphere. The SNR was calculated by determining the mean and the standard deviation in a 21 pixel-long section of the scan of the sphere's center. These measured results are listed in Table 14. The measurements were made close to, but not at, the exact typical radiance levels required by the specifications. The results have been scaled to the typical levels by changing the SNRs, assuming that the noise in the measurement varies as the square root of the change in signal level over this small range. These measured SNRs exceed the requirements of the specifications. However, the SNR measurements include the non-uniformity in the output of the sphere. This additional variation makes the measured values lower than the actual SNRs. SBRC has provided a calculation of the SNRs, based on the noise in the dark output from the instrument. These calculated values are also listed in Table 14. For purposes of evaluation, it seems reasonable to assume that the actual SNRs for SeaWiFS fall between the measured and calculated SNRs in Table 14. In all cases, however, the measured values (the lower limits for the actual SNRs) are better than the requirements in the specifications. Section 19 describes the model for instrument noise devised by the Project. The SNRs from this model fall between the measured and calculated values in Table 14. For the review 11

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PrelaunchAcceptance Report for the SeaWiFS Radiometer 02 0.1 x ,1 {3. v r" 0.0 A 0 U (/3 Cn C o -0.1 £ 8 1 i , _ i i i , i _ i i i i , i , i , r [ i , , i ! i i i ; I i i i , , r , v T -0.I Along Track (Pixels) 0.0 0.1 0.2 Fig. 5. Band-to-band registrationof SeaWiFS. The locationsof the individualband centersare given relativeto the average forthe eight bands. The distancesare given in "pixels,"where 1 pixel equals 1.6mrad. The figurealsoincludesa square that is0.1 pixelon each side and which is centered onthe average center locationforthe eight bands. prelaunch es- Table 13. Along-track band center measurements. panel, the resultsin Section 19 givethe best radi- The same procedure used to obtain the measured timates of the SNRs forthe instrument at the Ltypical However, those values remain prelaunch estimates. values in Table 12 was employed here. ances. An extensivesetof on-orbitmeasurements (McClain et al. Center Distance Distance 1992 and Woodward et al.1993) willbe used to obtain an Band Position from center from center improved set of SNRs. Table 12. Along-scan band center measurements. The measurements were made in ticks, with each tick equal to 0.1 mrad. The results are also given in mrad and in pixels, where one pixel is 1.6 mrad. The range gives the distance between the two bands that are farthest apart. Center Distance Distance Band Position from center from center No. [ticks] [mrad] [pixel] 1 57.56 -0.003 -0.002 2 56.71 -0.088 -0.055 3 58.08 0.049 0.031 4 57.03 -0.056 -0.035 5 59.00 0.141 0.088 6 58.26 0.066 0.041 7 57.52 -0.008 -0.005 8 56.58 -0.101 -0.063 Range 2.42 0.242 0.151 12 No. [ticks] [mrad] [pixel] 1 22.50 0.050 0.031 2 20.29 -0.170 -0.106 3 21.15 -0.085 -0.053 4 20.78 -0.121 -0.076 5 23.02 0.103 0.064 6 21.83 -0.016 -0.010 7 23.67 0.167 0.104 8 22.73 0.073 0.046 Range 3.37 0.337 0.210 11. POLARIZATION 11.1 Requirement The racliometric data shall be nominally insensitive to linear polarization. The polarization factor (PF) as defined below, shall be no greater than 2% over scan angles from +45 ° to -45 ° for allbands and tiltangles between -20 ° and +20 °. /max and Imin are the recorded maximum

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain and minimum output when the plane of incoming 100% data for band 1 are shown in Fig. 6. These data are replinearly polarized light is rotated through 180 ° . resentative of the results for bands 1-6. The input data show a dominant signal of 1 cycle per 360 ° and show an PF = Im_ - Imin < 0.020 (2) average value of 100. This allows a direct conversion of /max "b /rain the average-to-peak values from the Fourier analyses into percentages. Table 14. SNRs for the SeaWiFS Bands. The results of the Fourier analysis are summarized in Band Specified Measured Calculated Table 15. They are given in terms of the average-to-peak No. SNR SNR SNR values for the input to the Fourier transforms, for the one- 1 499 940 1107 cycle component, and for the two-cycle component. It 2 674 950 1269 is the two-cycle component that contains the information 3 667 1156 1402 about the polarization of the instrument. Since the aver- 4 640 1055 1373 age value for the measurements is 100, the average-to-peak 5 596 690 1242 values translate directly into percentages. 6 442 798 846 As shown in Table 15, the one-cycle Fourier compo- 7 455 860 971 nent accounts for almost half of the average-to-peak signal 8 467 670 796 in the data from bands 1-6. In the judgement of the review panel, the majority of the observed variation in the measurements of these bands does not come from polariza- 11.2 Compliance tion sensitivity in the SeaWiFS instrument. Presumably, Polarization is defined in this requirement in terms of the bulk of the variability derives from a non-uniformity in the polarizer plate used in the measurements. The efthe difference from the average for the output range. This fects of the polarizer plate repeat for each of the 6 bands definition then gives a polarization value that is half of for which the polarizer plate was used. The polarization the difference between the maximum output and the miniin the SeaWiFS instrument for these bands is less than mum output. The polarization sensitivity of SeaWiFS was 0.25%. checked using two linear sheet polarizers, at different times, between the light source and the instrument. The first polarizer (Polaroid HR) checked bands 1-6, and the second (Polaroid HN) checked the two near infrared (IR) bands-bands 7 and 8. Changes in the output of the instrument during these tests included variations in the light through the polarizers as well as polarization dependent changes in the output of the instrument itself. The variation in light through the polarizer is an artifact of the measurement procedure, since the rotation axis for the polarizer is not located at the center of the input aperture of the instrument. Crossed polarizers showed good extinction for each band, indicating that the polarizers were creating polarized light. Using knowledge of the expected angular dependence of the polarization effect, an effort was made to separate the instrument's portion of the polarization pattern. The po- Table 15. Summary of polarizationresults.The values in columns 3-5 are average-to-peak values, expressed as percentages. Band Input One-Cycle Two-Cycle No. to Transform Output Output 1 1.90 0.96 0.15 2 1.10 0.53 0.09 3 0.90 0.30 0.11 4 0.60 0.22 0.08 5 1.10 0.39 0.20 6 1.00 0.43 0.14 7 0.90 0.01 0.26 8 1.10 0.05 0.35 The test results for bands 7 and 8 show a pattern that larization measurements were made by rotating each polar- is similar for the two bands (see Fig. 7 for band 7). Howizer through 360 ° in 22.5 ° increments. Since polarization ever, the pattern is noticeably different from the pattern changes from a minimum to a maximum in 90 °, the re- for bands 1-6. Of course, bands 7 and 8 used the same posponse of the instrument should show two cycles, i.e., two larizer plate, a different polarizer plate than the one used maxima and two minima, in the 360 ° rotation. Fourier for measurements on bands 1-6. The patterns for bands analysis was used to look for the expected two cycle sinu- 7 and 8 show essentially no one-cycle component. In adsoidal function in the polarization results. dition, the two-cycle component in the pattern is some- The data were taken at 16 angles, from an arbitrarily what larger than for bands 1-6, falling between 0.25% and determined zero, through 360 ° , back to the original an- 0.35%. No instrument based explanation can explain why gular zero. The two measurements at 0 ° were averaged the polarization in SeaWiFS for bands 7 and 8 should be to give a data set with 15 points from 0 to 337.5 °. From different from that for the other 6 bands. For this reason, a the Fourier transform of these data, sinusoidal waveforms large part of the two-cycle Fourier component for bands 7 with 1-9 cycles per 360 ° were extracted for analysis. The and 8 appears to be an artifact caused by variations in the 13

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PrelaunchAcceptanceReportfortheSeaWiFSRadiometer polarizer plate for these bands. This assumption explains the similarity in the angular pattern for the measurements 13. QUANTIZATION on bands 7 and 8, in the same manner that it explains the 13.1 Requirement similarity in the patterns for bands 1-6. Thus, for all eight SeaWiFS bands, the polarization the instrument is estimated to be less than 0.25%. 12. DYNAMIC RANGE 12.1 Requirement The sensor shall be designed to operate over a dynamic range that extends from the noise floor (NEdL) in each spectral band to the maximum levels (Lcloud) given in Table 18. (There is an amendment to the Contract. With this addition, there are 3 radiance levels in the specifications: saturation radiance, maximum ocean radiance, and maximum cloud radiance. The specification radiances are given in Tables 16, 17, and 18, respectively.) 12.2 Compliance for themselves. The specification, which gives the saturation levels the eight SeaWiFS band, was supplemented by an amendment to the contract in August 1993. The amendment provides the maximum ocean radiances and the maximum Data shall be quantized at 10 bits. The differential in linearity of the quantizer(s) shall be better than one-half a least significant bit. 13.2 Compliance The data from SeaWiFS are quantized at 10 bits. The data from each detector in each band are digitized with 12-bit analog-to-digital (A/D) converters. For 4-to-1 Time Delay and Integration (TDI), the 12-bit values from each detector are summed to give a 14-bit value. The bottom four bits from this output are removed, with the upper 10 bits sent to SeaStar. Measurements by the instrument manufacturer (SBRC), using a voltage ramp, show linearity at better than one-half_of the least significant bit of the output 10 bits. This procedure was relatively easy, since the least significant bit for each detector corresponds to four times the least significant bit in the A/D converters, 14. MTF cloud radiances for the instrument. These changes to the 14.1 Requirement specifications were required due to the use of bilinear gains in SeaWiFS. However, the saturation values from the original specification remain an important part of the SeaWiFS measurements. The saturation values are the maximum radiances that the SeaWiFS bands would provide if the knees the point where the radiance vs. counts slope changes) the bilinear gains are ignored. The saturation values define the sensitivity of Sea WiFS, in counts per unit radiance, for the instrument's ocean measurements. In summary, the saturation radiances define the sensitivities of the SeaWiFS bands for ocean measurements, i.e., for measurements below the knees of the bilinear gains. The maximum ocean radiances are the radiances at the knees for the eight bands. The maximum cloud radiances mea- 14.2 Compliance axe the greatest values that the SeaWiFS bands will The MTF of the data shall equal or exceed the values tabulated in Table 19 below, in both the along-track and cross-track directions for a sine wave input. The Nyquist frequencyt has a spatial period equal to two IFOVs on the ground. in The MTF specifications shall be satisfied for modulations between dark and Ltypical and between dark and Lmax, for every detector element in each spectral band. Data describing the MTF shall be provided from prelaunch testing to verify that the specification is met. Data from lunar views and/or internal stabilized sources will also be provided for analysis of the MTF on orbit. sure. With the addition of the "maximum ocean" and the The SeaWiFS MTFs are calculated from the line spread "maximum cloud" radiances to the specifications in the functions in Fig. 1. They consist of the Fourier transforms contract amendment, the term "saturation" radiance has of the line spread functions. The results in Table 20, below, become a misnomer. However, the term has been retained here. use the MTF calculation program provided by SBRC. The values in the specification give minimum amplitudes for Table 16 gives the saturation radiances from the Sea- several low frequency sinusoidal waves from the Fourier WiFS calibration (ignoring the bilinear gain knees). Ta- analysis. The waves are given in terms of their wavelengths ble 17 gives the maximum ocean radiances, and Table 18 relative to the width (FWHM) of the field-of-view, i.e., in gives the maximum cloud radiances. All radiances are cal- cycles per pixel. culated in terms of miUiwatts per square centimeter per micrometer per steradian (mW cm- 2 # m - 1sr - 1). The dift The Nyquist frequency is the minimum sampling frequency ferences from the specifications are also calculated. They of a digital system sufficient to reconstruct the original inforare small, and present no problem with regard to specifi- mation. For SeaWiFS, the original information is the input cation compliance. 14 sequence of radiances.

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R.A.Barnes,W.L.Barnes,W.E.Esaias,andC.R.McClain 102 \ 101 ,...... bl i i00 -O- 99 98 0 i 2 3 4 5 6 7 a) 102 lOI -4 • \ blk _ I 100 _../? -99 / 98 x k 337.5 b) Io2 i ' _ _ iOl _ -- 100 + 99 98 0 x k 337.5 d) %. / 8 9 10 I1 12 13 14 15 i 1 0.5 / diff k o / \ _.5 !\ i -I 0 x k 337.5 c) 0.2 O.l ',, / \ / diffk 0 \i \ I "-0.2 0 x k 337.5 e) Fig. 6. Polarization measurements for SeaWiFS band 1. a) The instrument response measured at 22.5 ° increments of polarizer rotation. These values are the input values for Fourier analysis, b) The polarization values with and without the one-cycle component bl (k) equal the measured values, and h(k) equal the measured values without the one-cycle component, c) The one-cycle polarization component generated by Fourier analysis, d) The polarization values with and without the two-cycle component bl(k) equal the measured values and h(k) equal the measured values without the two-cycle component. e) The two-cycle polarization component generated by Fourier analysis. 15

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PrelaunchAcceptanceReport for the SeaWiFS Radiometer 102 101 b7 i 100 fr 99 98 0 I 2 3 4 5 6 102 I01 --I00 ,' 99 / J 98 i 0 x k 337.5 b) 102 101 ,,,--,oo-_ :'\ / ','- 99 98 0 xk 337.5 d) 7 8 9 10 I1 12 ]3 14 15 i -) 0.1 0.05 ,,.,._ _----d " _' _ .-..IL 0 __--, -0.05 -0.1 337.5 0 Xk c) 0.3 0.15 -. o / \ / i\ -0.15 / ',, -0.3 0 x k 337.5 o) Fig. T. Polarization measurements for SeaWiFS band 7. a) The instrument response measured at 22.5 ° increments of polarizer rotation. These values are the input values for Fourier analysis, b) The polarization values with and without the one-cycle component b7(k) equal the measured values, and h(k) equal the measured values without the one-cycle component, c) The one-cycle polarization component generated by Fourier analysis, d) The polarization values with and without the two-cycle component b7(k) equal the measured values and h(k) equal the measured values without the two-cycle component. e) The two-cycle polarization component generated by Fourier analysis. 16

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R.A.Barnes,W.L. Barnes,W.E.Esaias,andC.R.McClain Table 16. SeaWiFS saturation radiances (in mW cm-2# m-isr-i). The measured and specified saturation radiances appear in columns 3 and 4, respectively. Band Measured No. Gain Radiance 13.76 13.44 10.52 9.22 7.47 4.25 3.02 2.15 Specified Percent Radiance Difference 13.63 1.0 13.25 1.4 10.50 0.2 9.08 1.5 7.44 0.4 4.20 1.3 3.0O 0.5 2.13 1.0 Average % Difference 0.9 Greatest % Difference 1.5 Least % Difference 0.2 Table 17. SeaWiFS maximum ocean radiances (in mW cm-2# m-1st-i). The measured and specified ocean radiances appear in columns 3 and 4, respectively. Band Measured No. Gain Radiance 10.90 10.56 8.18 7.16 5.74 3.25 2.29 1.64 Specified Percent Radiance Difference 10.84 0.5 10.46 0.9 8.19 -0.1 7.05 1.6 5.74 0.0 3.21 1.2 2.29 0.0 1.62 1.0 Average % Difference 0.6 Greatest % Difference 1.6 Least % Difference -0.1 Table 18. SeaWiFS maximum cloud radiances(inmW cm-2/_ m-isr - i).The measured and specifiedcloud radiances appear in columns 3 and 4, respectively. Band Measured No. Gain Radiance 60.16 67.91 68.21 66.47 64.97 54.93 42.98 34.38 Specified Percent Radiance Difference 60.02 0.2 66.24 2.5 68.17 0.I 65.62 1.3 65.16 -0.3 53.78 2.1 42.95 0.I 34.05 1.0 Average % Difference 0.9 Greatest % Difference 2.5 Least % Difference -0.3 17

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Prelaunch Acceptance Report for the SeaWiFS Radiometer instru- 16. TRANSIENT RESPONSE The MTF gives an idea of the response of the ment to variations in the input radiance, both along-scan and along-track. For example, consider a case in which 16.1 Requirement the instrument scans across a scene with a variation of the input radiance having a sinusoidal shape and a spatial period of two pixels per period. In this case, the scene varies at the Nyquist frequency. According to the specification, the output from the sensor should show a variation (from pixel to pixel) across the scene that is greater than 30% of the amplitude of input sinusoidal radiance variation. Table 19. MTF requirements for spatial resolution. Frequency/ MTF Nyquist Frequency 0.00 1.0 0.25 0.9 0.50 0.7 0.75 0.5 1.00 0.3 15. GAINS 15.1 Requirement are quantization of the data. Band independent gains shall be provided, which commandable band by band, and which will increase decrease sensitivity according to the following: s. = G. × S, where Si and Sn are the initial detector signal and the signal with gain, respectively, and Gn is the gain factor at gain setting n. The nominal Gn values for gain settings of n equal to 2, 3, and 4 shall be based on the values Table 21. These G values include those required for onboard solar and lunar capabilities. The values of G will be within 5% of the specifications in Table 21, and shall be known relative to G1 = 1 with an accuracy of greater than 99.5%. The nominal Gn value for n = 2 is 2. 15.2 Compliance Radiometric data should be relatively free of effects of overshoot and ringing when the IFOV scans across a steep gradient in radiance, from a maximum radiance of Lcloud to a minimum radiance of Ltypical. For this radiance step change, the output signal shall settle to within 0.5% of its final value within 10 IFOVs. 16.2 Compliance 16.2.1 Original Specification The original SeaWiFS specification describes the required response of the instrument when it scans across a steep gradient in radiance. The specification describes a gradient that is expected be found on orbit, i.e., from the radiance level for a cloud (Lcloud) to the typical radiance level for ocean measurements (Ltypic_). The original specification requires that the output from the instrument settles to within 0.5% of its final value (Ltypical) within 10 pixels. This limit, calculated in counts using values from the specifications, is given in Table 22. Since the values are small, the limit is given to 0.1 count relative to the or During the April 1993 SeaWiFS Pre-Ship Review, it was determined that the instrument did not meet the original bright target recovery (BTR) specification. At that (3) time, it was decided that the instrument manufacturer would rework SeaWiFS to improve its stray light characteristics. The series of modifications included the tilting of filters, incorporation of bilinear responses and corresponding changes to gains, refiguring the polarization scrambler, in and testing. The modifications did not include changes to the instrument's focal planes. A description of the revised BTR specification is given in the following section. The discussion presented here centers on the performance of the reworked SeaWiFS radiometer only with respect to the original specifications. The results in Table 23 were derived from laboratory measurements using the output of the SBRC integrating sphere. The measurements were made in four sets---one re-evaluated for each focal plane in the instrument. Color glass filters Gain values for gain settings 3 and 4 were Gains were placed over the output from the sphere in order to in the summer of 1993 during a meeting at OSC. 3 and 4 are used for solar and lunar measurements. The give a spectral shape which approximated the sun over the solar wavelength range of the bands on each of the four focal SCADP contains the predicted on-orbit lunar and ground planes. Cross-talk between bands on a focal plane is a diffuser radiances. They have been derived from based solar and lunar measurements at SBRC (Biggar et significant factor in the recovery of the instrument from al. 1993). The values presented in Table 21, below, for a pixel wide slit. appropriate for those radiances. The gains are given 4:1 TDI. orbit. required for the instrument to settle to less than 0.5% of These relative gain values can be measured on day Ltypical, using the counts given in Table 22. For bands 1- Current plans will have these values checked twice a at the start of the mission. 18 are bright targets. The measurements were made for a three The results in Table 23 give the distance, in pixels, 5, the results give the pixels required to settle to 3 counts

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R.A.Barnes,W.L.Barnes,W.E.Esaias,andC.R.McClain Table 20. MTF calculations for SeaWiFS. The amplitude is shown for each band at four different wavelengths: 0.500, 0.375, 0.250, and 0.125 cycles per pixel. Band Along-Scan MTF Amplitude Along-T_ack MTF Amplitude No. 0.500 0.375 0.250 0.35 0.57 0.76 0.36 0.58 0.76 0.36 0.58 0.77 0.36 0.58 0.77 0.35 0.57 0.76 0.37 0.59 0.78 0.39 0.61 0.79 0.34 0.55 0.74 Minimum Amplitude 0.30 0.50 0.70 above background. For bands 6-8, the results give the pixels required to settle to 2 counts. Table 23 also gives 0.125 0.500 0.375 0.250 0.125 0.93 0.44 0.65 0.84 0.96 0.92 0.41 0.62 0.81 0.95 0.93 0.41 0.62 0.82 0.95 0.93 0.40 0.61 0.81 0.95 0.93 0.48 0.67 0.84 0.96 0.93 0.43 0.63 0.82 0.95 0.94 0.49 0.68 0.85 0.96 0.91 0.47 0.66 0.83 0.96 0.90 0.30 0.50 0.70 0.90 radiances between 0.2 Ltypical and 0.9 Lm_x, the absolute radiometric accuracy shall be within :k6%. Measurements the number of pixels required for the instrument to settle to of the accuracy shall be made, as a minimum, at scan anzero counts after illumination by the slit. All eight bands settle to less than the specification limit within 10 pixels. Table 21. SeaWiFS gain values. These values are given relative to gain 1. The nominal value for gain setting 2 is 2. Band No. G1 G2 G3 G4 1 1 1.931 1.302 1.642 2 1 1.940 1.303 1.648 3 1 1.951 0.900 1.655 4 1 1.955 0.796 1.658 5 1 1.961 0.652 1.579 6 1 1.969 0.376 0.671 7 1 1.969 0.323 0.583 8 1 1.975 0.272 0.507 16.2.2 Revised BTR Specification In the summer of 1993, there was a meeting at OSC in Chantilly, Virginia. At that meeting, a set of improvements to ameliorate stray light in SeaWiFS was discussed. Each proposed improvement was presented, accompanied by a corresponding estimate of the resulting improvement to performance of the instrument. A final and accepted set of instrument improvements from that meeting was incorporated into a Contract modification. As demonstrated by SBRC testing, this set of modifications has created the anticipated improvements to the performance of the sensor. However, as described above, the reworked SeaWiFS radiometer also meets the original BTR specifications. 17. ABSOLUTE ACCURACY 17.1 Requirement An absolute radiometric accuracy of 5% (1 a) shall be achieved at the typical spectral radiance levels. At spectral gles centered at 0 °, -40 ° , and +40 °; tilt angles of 0 °, -20 ° , and +20°; special tilt angles, should they be required, used to view the moon; and at all gains. 17.2 Compliance 17.2.1 Accuracy at Nadir This specification calls for an absolute radiometric calibration at the 5% level. The SeaWiFS instrument was calibrated radiometrically by the manufacturer (SBRC) using an integrating sphere that was calibrated with standards that are traceable to the National Institute of Standards and Technology (NIST). In additiofi, the SBRC sphere has been compared with the GSFC sphere, which has also been calibrated using standards traceable to NIST. The comparison of the GSFC and SBRC spheres showed agreement at the 2% level. Fundamentally, the accuracy of the radiometric calibration of SeaWiFS reduces to the accuracy of the calibration of the integrating sphere. The absolute uncertainty in the radiances from the sphere is the largest of the set of uncertainties in the instrument calibration. In addition, many uncertainties in the radiometric calibration of SeaWiFS, such as the alignment of the sphere and the instrument, duplicate uncertainties in the calibration of the sphere, such as the alignment of the sphere, the radiance standard, and the transfer instrument. The current understanding of the uncertainties in the calibration of the GSFC sphere is reported by Walker et al. (1991). Two of the authors specialize in radiometric calibrations at NIST, and the third author is the principal investigator for the GSFC sphere. In the abstract, Walker et al. (1991) states: "Recent measurements performed at NIST and NASA Goddard Space Flight Center have demonstrated that the uncertainty of sphere-source radiance measurements can be improved from the present 19

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PrelaunchAcceptance Report for the SeaWiFS Radiometer Table 22. Constants used in the calculation of the specification count limit. The Lclou d and Ltypica l values come from the performance specifications. The slopes (or sensitivities for each band) come from the SBRC calibration data. Band Lcloud Ltypical Lcloud Radiance 0.5% of No. [mW cm-2# m-lsr - 1] [roW cm-2# m-lsr - 1] Ltypical per Count Ltypical [counts] 1 60.0 9.10 2 66.2 8.41 3 68.2 6.56 4 65.6 5.64 5 65.2 4.57 6 53.8 2.46 7 43.0 1.61 8 34.0 1.09 5-10% level to a 1-2% level." This is a general statement about the technique for calibrating sphere sources. 6.59 0.0137 3.3 7.87 0.0134 3.1 10.4 0.0105 3.1 11.6 0.00920 3.1 14.3 0.00746 3.1 21.9 0.00425 2.9 26.7 0.00301 2.7 31.2 0.00215 2.5 dent check method has not been determined. More work willhave to be done ifthisproblem isto be resolved." However, it does not describe the actual uncertainty in Recent discussionsindicatethat error propagation in radiances from the GSFC sphere. Table 23. This table shows the SeaWiFS BTR characteristics. Column 2 gives the value of 0.5% of Ltypical, in counts, for each band. The instrument response must settle below this level of residual counts after scanning a bright target. Column 3 shows the number of pixels after the slit required for the instrument to settle to the level of the specified residual counts. Column 4 provides the number of pixels the instrument requires to settle to a level of zero residual counts. Band Residual Cnts. Pixels to Pixels to No. (0.5% Ltypical) Spec. Zero Cnts. 1 3.3 6 10 2 3.1 5 9 3 3.1 7 10 4 3.1 5 15 5 3.1 9 15 6 2.9 7 9 7 2.7 9 11 8 2.5 7 10 At the conclusion of the report, Walker et al. (1991) NASA's independent check method has not changed. The discrepancy between the NASA 5-10% errorestimate and the I-2% estimate in Walker et al. (1991) remains unresolved.This assessment has ledto the conclusionthat the uncertaintyin the radiances from the GSFC sphere is in the range of 2-5%. This conclusionis nothing more than an educated guess. If the 2-5% uncertainty in the GSFC sphere iscorrect,and ifthe GSFC and SBRC spheres agree at the 2% level,then the estimateof the uncertaintyin the SBRC sphere is2-5%. This isalsothe review panel'sestimate for the uncertainty in the calibration of SeaWiFS. 17.2.2 Accuracy Over a Scan Line These measurements were made at nadir. The specifications also call for a 5% accuracy at scan angles of +40 ° and -40 °. SBRC has made measurements to check the output of the instrument at scan angles 20 ° , 40 ° , and 58 ° on both sides of nadir. The results of the measurements at these angles give the instrument output relative to the output at nadir; this effect is called scan modulation. A fitted curve to the scan modulation gives a correction that is good to 0.5% at all scan angles. This correction has been incorporated into the data reduction procedures for states: '_rhe normal stated uncertainty for the NASA cal- SeaWiFS. The absolute radiometric calibration of the inibration of their large-area sphere source is presently 5- strument remains within 5% over its entire scan range. 10%. The repeatability of the calibration from month to month is about 1 percent. The major contributors to 17.2.3 Accuracy Over Tilt Angles NASA's large overall uncertainty are the uncertainties asthe The specification calls for the radiometric calibration sociated with the standard lamp, the dimensions of and to be known at all tilt angles. For SeaWiFS, the entire apertures, the distance measurement, the alignment, of scanner tilts, including all components from the optical the lamp current of the sphere source lamps. The results our measurements confirmed the accuracy of the spectra/ irradiance method employed by NASA, and in the future of angle is not considered a factor in the radiometric accuracy it will permit them to state uncertainties in the range 1-2%. The reason for the difference in NASA's indepen- 2O inlet to the focal planes. The optical path through the instrument does not change as a function of tilt angle. Tilt of SeaWiFS.

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain 18. RELATIVE ACCURACY 18.1 Requirement The design shall be capable of achieving an accuracy within 2% (1 a) relative to the sun. The calibrated data shall be linear to within +1% over the full range of input signals. 18.2 Compliance 18.2.1 Accuracy Relative to the Sun The instrument shall be capable of achieving an accuracy, within 2%, relative to the sun. SBRC has made field measurements of the solar flux in March 1993 and in October 1993. Atmospheric transmission measurements for these two field measurements were made by the University of Arizona (Biggar et al. 1993). The differences in the predicted on-orbit solar measurements from these two field tests averaged 1.5%. The greatest difference was 3.6% in band 8. These field measurements include uncertainties in the measurement of the atmospheric transmission that may amount to 2 or 3%. The field test results also show a consistency in the SeaWiFS solar measurements at the 2-3% level. However, with the error source of atmospheric transmission, ground based measurements cannot confirm an accuracy of 2% in the SeaWiFS solar measurements. They do, however, give some confidence that the instrument is capable of that accuracy. 18.2.2 Linearity 18.2.$.1 February 1993 Measurements The measurements presented here were made in February 1993. They were taken during the radiometric calibration of the instrument. The radiance measurements were of the sensitivity at each light level from the average sensitivity for the band was calculated. These differences should be less than 1%. Except for one outlier in each band, all differences are observed to be less than 1%. For light level 7, each band shows the sensitivity to be between 1.4% and 1.9% higher than the other levels. The review panel feels that this discrepancy does not come from the instrument, but from the calibration of the integrating sphere. It occurs at one light level, and it is present in all bands. With the knowledge of this discrepancy, the average values for the bands in Table 24 have been calculated without the sensitivity for light level 7. The inclusion of this light level skews the results for the remaining measurements. In addition, it is interesting to note that the linearity of the SeaWiFS measurements is sufficiently good to reveal a 1.5-2.0% inconsistency in the calibration of the integrating sphere. It should also be noted that the consistency of the calibration of the sphere is an integral part of the linearity measurement. 18.2.2.2 November 1993 Measurements Although not reported in the SCADP, a set of linearity measurements was made by SBRC for the eight SeaWiFS bands in November 1993. The results of these measurements are given in Table 25. The sensitivity of each band is presented in the table at three radiance levels, approximating Ltypical, two-thirds Ltypical, and one-third Ltypica I. The least linear of the bands in Table 25 is band 2, with differences of 1.2% and 1.3% from the average sensitivity. As discussed above, the consistency in the calibration of the sphere is a fundamental part of these results. The review panel feels that imprecision in the repeatability of the $BRC integrating sphere output has created a substantial portion of these differences. The repeatability of band 2 from the February 1993 measurements in Table 24 is significantly better than that in Table 25. As a result, the review panel concludes that the linearities of the eight made at eight light levels to cover the radiance ranges of SeaWiFS bands meet specification. the SeaWiFS bands. The results from those measurements are given as the averages of 25 individual measurements for each band (see Table 24). Due to the spectral shape of the The results in Table 24 also indicate that the response of the SeaWiFS bands are linear at low radiance levels. As shown for bands 1 and 2 in Table 24, the response of light from the integrating sphere, only SeaWiFS band 1, the instrument is linear for radiance levels corresponding at 412 nm, produced output that did not saturate at any of the radiance levels. For SeaWiFS band 2, light level 1 caused the output to saturate. For that band and that light level, the band produced only its maximum digital output. For band 3, two of the radiance levels caused the band to saturate. This sequence continued up to band 8, which saturated for seven of the eight light levels. However, this final light level was sufficient for the radiometric calibration of band 8. Table 24 gives the sensitivity for SeaWiFS bands 1-4 at each light level. It is the consistency of the instrument's sensitivity with light level that is required by the specifications. To check this sensitivity, the difference (in percent) to output from 15-50 counts. Table 24 lists only the results for SeaWiFS bands 1-4. The results for the other four bands are consistent with those presented here, at least to the extend that they can be checked. For band 8 in particular, it is difficult to check linearity using one point only. 19.0 SYSTEM NOISE 19.1 Requirement The SNR shall be determined for all bands at a sufficient number of spectral radiance levels between 0.2 Ltypic_ 21

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PrelaunchAcceptanceReportfortheSeaWiFSRadiometer Table 24. SeaWiFS radiometric measurements given for four SeaWiFS bands at eight light levels. The sensitivity for each band is calculated for each light level. The differences are the percent differences for the average sensitivity for each band. See text for details. Band Light Counts Offset Net Radiance Sensitivity Difference No. Level Counts [mWcm-2um-lsr -1] [radiance/count] [%] 1 1 842.77 2i.76 821.01 2 435.54 21.76 413.78 3 257.50 21.76 235.74 4 194.59 21.76 172.83 5 111.85 21.76 90.09 6 54.03 21.76 32.27 7 39.60 21.76 17.84 8 36.98 21.76 15.22 Average sensitivity 0.014380 2 1 Band output saturates 2 710.43 19.46 690.97 3 413.26 19.46 393.80 4 308.19 19.46 288.73 5 170.34 19.46 150.88 6 73.63 19.46 54.17 7 49.35 19.46 29.89 8 44.90 19.46 25.44 Average sensitivity 0.013814 3 1 Band output saturates 2 Band output saturates 3 872.75 21.05 851.70 4 646.69 21.05 625.64 5 349.98 21.05 328.93 6 139.07 21.05 118.02 7 86.97 21.05 65.92 8 75.92 21.05 54.87 Average sensitivity 0.010874 4 1 Band output saturates 2 Band output saturates 3 Band output saturates 4 897.99 20.80 877.19 5 482.88 20.80 462.08 6 186.47 20.80 165.67 7 113.04 20.80 92.24 8 97.02 20.80 76.22 Average sensitivity 0.009361 and 0.9 Lma_ to characterize the signal dependence of the system noise. 19.2 Compliance The SNRs for the eight SeaWiFS bands have been measured near Ltypical. These measurements were made using the SBRC integrating sphere. Uncertainties in the output of the sphere, both over the area of the output aperture and 22 11.80 0.014373 -0.1 5.97 0.014428 0.3 3.40 0.014423 0.3 2.49 0.014407 0.2 1.29 0.014319 -0.4 0.46 0.014255 -0.9 0.26 0.014574 1.4 0.22 0.014455 0.5 9.56 0.013836 0.2 5.45 0.013840 0.2 3.99 0.013819 0.0 2.08 0.013786 -0.2 0.75 0.013845 0.2 0.42 0.014052 1.7 0.35 0.013758 -0.4 9.28 0.010896 0.2 6.80 0.010869 -0.0 3.56 0.010823 -0.5 1.28 0.010846 -0.3 0.73 0.011074 1.8 0.60 0.010935 0.6 8.19 0.009337 -0.3 4.30 0.009306 -0.6 1.55 0.009356 -0.1 0.88 0.009540 1.9 0.72 0.009446 0.9 over short intervals of time, have caused a small (but significant) decrease in the SNRs from these measurements. SBRC has created a model of their instrument noise, based on dark noise measurements and on the electronic design of the instrument. These model-based SNRe are slightly higher than the measured values at Ltypical, which is in agreement with the review panel's understanding of the measurements. The SeaWiFS SNR model gives the calculated results

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R.A.Barnes,W.L.Barnes,W.E.Esaias,andC.R.McClain Table25. SeaWiFSradiometricmeasurementsgivenforall bandsat three light levels. The differences are the percent differences from the average sensitivity for each band. These measurements were made in November 1993. Band Counts Offset Net Radiance Sensitivity Difference No. Counts [mW cm- 2# m - 1st - 1] [radiance/count] [_] 1 695.60 20.84 674.76 516.70 20.84 495.86 268.60 20.84 247.76 Average sensitivity 0.013768 2 701.30 18.00 683.30 491.60 18.00 473.60 258.30 18.00 240.30 Average sensitivity 0.013532 3 709.00 20.45 688.55 503.80 20.45 483.35 248.50 20.45 228.05 Average sensitivity 0.010522 4 699.50 20.12 679.38 480.30 20.12 460.18 248.60 20.12 228.48 Average sensitivity 0.009220 5 703.30 22.00 681.30 527.60 22.00 505.60 281.40 22.00 259.40 Average sensitivity 0.007474 6 590.60 23.10 567.50 450.90 23.10 427.80 195.70 23.10 172.60 Average sensitivity 0.004259 7 706.50 22.73 683.77 347.10 22.73 324.37 209.60 22.73 186.87 Average sensitivity 0.002985 8 526.40 20.14 506.26 365.50 20.14 345.36 210.30 20.14 190.16 Average sensitivity 0.002131 from the SBRC generated values for instrument noise. The SBRC results give the SNRs for the eight SeaWiFS bands at three radiance levels: Ltypical, one-half Ltypicah and one- 9.246 0.013703 -0.5 6.817 0.013748 -0.1 3.432 0.013852 0.6 9.122 0.013350 -1.3 6.485 0.013693 1.2 3.257 0.013554 0.2 7.216 0.010480 -0.4 5.076 0.010502 -0.2 2.414 0.010585 0.6 6.212 0.009144 -0.8 4.223 0.009177 -0.5 2.134 0.009340 1.3 5.073 0.007446 -0.4 3.791 0.007498 0.3 1.940 0.007479 0.1 2.427 0.004277 0.4 1.835 0.004289 0.7 0.727 0.004212 -1.1 2.057 0.003008 0.8 0.966 0.002978 -0.2 0.555 0.002970 -0.5 1.075 0.002123 -0.4 0.734 0.002125 -0.3 0.408 0.002146 0.7 the counts and from their associated SNRs in the SCADP data. The counts of noise for one-quarter Ltypical in bands 3 and 4 in the SBRC data were smaller than the accepted quarter Ltypicaa. The Ltypical radiance levels are listed in value for digitization noise (0.289 count). As a result, it Barnes and Holmes (1993). They are also given as part was concluded that digitization noise had not been incorof Table 26. The prelaunch calibration coefficients used to porated into the SBRC data. Digitization noise is included convert the counts from the instrument into the measured radiance and vice versa are found in Table 6 of Barnes et al. (1994). The model presented here gives the noise from each band, in counts, as a function of the number of counts in the measurement by that band. The noise values that form the basis for the model have been calculated from in the SeaWiFS noise model presented in Table 26. The addition of digitization noise to the model lowers the SNRs in the model's results. However, the model SNRs remain slightly higher than the measured results. Noise values from the calibration data show a strong linear dependence with the measured counts. Based on this linear dependence, a noise value for each band has 23

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PrelaunchAcceptanceReportfor the SeaWiFS Radiometer Table 26. SNRs calculated from the SeaWiFS noise model. The noise model is a linear function of the counts from each SeaWiFS band. This model is given for the standard gain (gain 1) and the standard detector configuration (TDI 4) for the SeaWiFS ocean measurements. noise. The noise values in the model incorporate digitization Ltypical Ltypical Noise Intercept Noise Slope Noiset SNR Band No. [mWcm-2pm-lsr -1] [counts] 9.10 638.4 8.41 618.2 6.56 613.0 5.64 612.2 4.57 607.1 2.46 584.9 1.61 531.6 1.09 513.5 Noise at Ltypical forSea- ment to meet the specifications for that band. However, been calculatedforzeroradiance.The noisemodel model the measured results for band 5 in the SCADP data are WiFS band 7 isshown in Fig. 8. The linearnoise [counts] [counts/count] [counts] at Ltypical 0.420 0.0003528 0.645 990 0.372 0.0003141 0.566 1,091 0.348 0.0002875 0.524 1,170 0.352 0.0002928 0.531 1,152 0.375 0.0003178 0.568 1,069 0.510 0.0004083 0.749 781 0.424 0.0003674 0.619 859 0.494 0.0004144 0.707 726 slopes)are also substantially lower than those from previous laboraforthe eight SeaWiFS bands (interceptsand in Ta- tory measurements by SBRC. The review panel feels that given in Table 26. For the review panel,the SNRs ble 26 give the best prelaunch estimatesof the SNRs the instrument at the Ltypic_levels. scan the other seven bands, remains a prelaunch estimate. An As part of the SCADP data, there is a complete for the value of 1,069 from Table 26 gives a more proper value for the SNR for band 5. This value, along with those for lineofdata from the thirdoutdoor fieldteston 1 November extensive series of on-orbit measurements (McClain et al. 1993. A descriptionof the components of a solar scan 1992 and Woodward et al. 1993) will be used to obtain For three of an improved set of SNRs. A summary of the prelaunch lineare given in Woodward et al.(1993). the SeaWiFS bands, the solar diffusermeasurements are SNR model for SeaWiFS bands 1-4 is presented in Tamade using gain 1. The resultsforthese bands from the ble 28. A similar summary for bands 5-8 is presented in fieldtest are given in Table 27. They are based on the Table 29. average counts from 25 consecutivemeasurements across the diffuser.The noise values in Table 27 representone 20. POINTING KNOW"LEDGE standard deviationabout each average.The linearmodel intothe Pointing knowledge is a system level requirement. It in Table 26 is used to convert those noise counts 5 in includes knowledge of the nadir vector and scan plane of noise values at Ltypical. The SNRs for bands 3, 4, and Table 27 compare favorably with those in Table 26. Table 27. Measured SNRs from a SeaWiFS solar scan. For bands 3, 4, and 5, the solar diffuser measurements are made using gain 1. The noise model in Table 26 is used to convert the noise values from the measured count levels to those at Ltypic_. These SNRs compare favorably with those in Table 26. Band Average Noise Noiset SNRt No. Counts [counts] [counts] 3 282.0 0.400 0.495 1,238 4 331.2 0.431 0.513 1,193 5 421.5 0.571 0.630 963 t At Ltypical scan SCADP. These coordinates are given with respect to a set For the review panel, the results from the solar SNR of transfer mirrors mounted on the radiometer. These valindicate that there has been a problem with SBRC of which ues, from the instrument, are only part of the information measurements for band 5 (Section 10), the cause calibra- required for pointing knowledge, since OSC must transfer is undetermined. The SBRC measurements for the instru- these coordinates into their own system for the spacecraft tion data book (SNR of 690 for band 5) show the 24 the instrument relative to the spacecraft; of the location of the spacecraft on orbit; and of the yaw, pitch, and roll angles of the spacecraft relative to the Earth. 20.1 Requirement The contractor shall provide in the down[inked data stream, data describing the spacecraft attitude and location and sensor pointing angles required for calculation of the location (in latitude and longitude) of each ocean IFOV to within one IFOV at all scan and tilt angles. 20.2 Compliance SBRC has provided OSC with the pointing coordinates for the SeaWiFS radiometer, information also found in the

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain 0.8 SeoWiFS -.Bond 0.7 ...06 0.5 .-_ 0•4 O Z -0.3 0 0.2 0.1 (3 0.0 0 ........ ........ Signol (counts) 1200 SeoWiFS - Bond 7 • m _ ° "G'IO00 0 c 800 E 0 600 0 0 z 400 I I 0 . 200 0 f||l|lllllJilWllllilgllllllllllllWlll'l 0 200 Signol (counts) 7 ,00'........ ....... 860 " I 400 600 800 Fig. 8. Results of the noise model for SeaWiFS band 7. The input values for the model come from the SBRC calibration data book. The top figure shows the noise model for SeaWiFS. The curve gives the results of the noise model. The symbols give the input noise values at Ltypical, one-half Ltypical, and one-quarter Ltypical. These three values include digitization noise• The bottom figure displays the calculated SNRs for SeaWiFS. The curve gives the calculated results from the model. The symbols give the input values from SBRC, with digitization noise added. 25

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PrelaunchAcceptanceReportforthe SeaWiFSRadiometer Table 28. SNR model for SeaWiFS bands 1-4. The counts at each reference level are calculated using Table 6 of Barnes et al. (1994).The noisevalues are calculatedusing Table 20. Radiance Band 1 Band 2 Band3 Band4 Counts SNR Counts SNR Counts SNR CouPs SNR [mW cm-2_ m-lsr - I] 11.30 793 1,133 11.10 779 1,121 10.90 765 1,109 10.70 751 1,096 10.50 737 1,083 10.30 723 1,071 I0.I0 709 1,058 9.90 695 1,044 9.70 680 1,031 9.50 666 1,017 9.30 652 1,003 9.10 638 989 8.90 624 975 8.70 610 961 8.50 596 946 8.30 582 931 8.10 568 916 7.90 554 900 7.70 540 885 7.50 526 869 7.30 512 853 7.10 498 836 6.90 484 819 6.70 470 802 6.50 456 785 6.30 442 767 6.10 428 749 5.90 414 731 5.70 400 713 5.50 386 694 5.30 372 675 5.10 358 655 4.90 344 635 4.70 330 615 4.50 316 594 4.30 302 573 4.10 288 552 3.90 274 530 3.70 260 507 3.50 246 485 3.30 232 461 3.10 217 438 2.90 203 414 2.70 189 389 2.50 175 364 2.30 161 338 2.10 147 312 26 787 1,271 772 1,256 757 1,242 742 1,227 728 1,212 713 1,196 698 1,181 684 1,165 669 1,149 654 1,133 640 1,116 625 1,100 610 1,083 776 1,358 595 1,065 757 1,338 581 1,048 738 1,318 566 1,030 719 1,297 551 1,011 701 1,275 537 993 682 1,254 522 974 663 1,231 771 1,334 507 955 645 1,209 749 1,311 493 935 626 1,186 727 1,287 478 915 607 1,162 706 1,263 463 895 589 1,138 684 1,238 448 874 570 1,114 662 1,213 434 853 551 1,088 640 1,187 419 832 533 1,063 619 1,160 404 810 514 1,037 597 1,133 390 788 495 1,010 575 1,105 375 766 477 983 554 1,077 360 742 458 955 532 1,048 346 719 439 926 510 1,018 331 695 420 897 488 987 316 671 402 867 467 955 301 646 383 836 445 923 287 621 364 805 423 889 272 595 346 773 402 855 257 568 327 740 380 820 243 541 308 706 358 784 228 514 290 672 336 747 213 486 271 636 315 709 198 457 252 600 293 669 184 428 234 563 271 629 169 398 215 524 250 587 154 367 196 485 228 544

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain Table 28. (cont.) SNR model for SeaWiFS bands 1-4. The counts at each reference level are calculated using Table 6 of Barnes et al. (1994). The noise values are calculated using Table 20. Radiance Band 1 Band 2 Band 3 Band 4 [mWcm-2_ m-lsr -z ] Counts SNR Counts 1.90 133 285 140 1.70 119 258 125 1.50 105 230 110 1.30 91 202 96 1.10 77 173 81 0.90 63 143 66 0.70 49 112 51 0.50 35 81 37 0.30 21 49 22 0.10 7 17 7 SNR Counts SNR Counts SNR 336 178 445 206 500 304 159 403 185 454 271 140 361 163 407 238 121 317 141 359 203 103 272 119 309 168 84 226 98 257 133 65 178 76 203 96 47 129 54 148 58 28 79 33 90 20 9 27 11 31 Table 29. SNR model for SeaWiFS bands 5-8. The counts at each reference level are calculated using Table 6 of Barnes et al. (1994). The noise values are calculated using Table 20. Radiance Band 5 Band 6 Band 7 Band 8 [mW cm-2# m- lsr- 1] Counts SNR Counts SNR Counts SNR Counts SNR 5.75 764 1,237 5.65 751 1,223 5.55 737 1,210 5.45 724 1,197 5.35 711 1,183 5.25 697 1,169 5.15 684 1,155 5.05 671 1,141 4.95 658 1,126 4.85 644 1,111 4.75 631 1,096 4.65 618 1,081 4.55 604 1,066 4.45 591 1,050 4.35 578 1,034 4.25 565 1,018 4.15 551 1,002 4.05 538 985 3.95 525 969 3.85 511 951 3.75 498 934 3.65 485 916 3.55 472 899 3.45 458 880 3.35 445 862 3.25 432 843 3.15 418 824 749 3.05 405 804 725 2.95 392 785 701 2.85 379 764 678 2.75 365 744 654 2.65 352 723 630 918 900 881 861 842 821 27

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Prelaunch Acceptance Report for the SeaWiFS Radiometer Table 29. (cont.) SNR model for SeaWiFS bands 5-8. The counts at each reference level are calculated using Table 6 of Barnes et al. (1994). The noise values are calculated using Table 20. aaEliance Band5 Band 6 Band 7 Band8 m-lsr -1] Counts SNR Counts SNR Counts SNR Counts SNR [mW cm-2D 2.55 339 702 606 800 2.45 325 680 582 779 2.35 312 658 559 757 2.25 299 636 535 734 743 1,066 2.15 286 613 511 711 710 1,037 2.05 272 590 487 687 677 1,006 1.95 259 566 464 663 644 975 1.85 246 542 440 638 611 942 1.75 232 518 416 612 578 908 1.65 219 493 392 585 545 873 369 558 512 836 730 917 1.55 206 468 345 530 479 .798 683 879 1.45 193 442 1.35 179 415 321 501 446 758 636 840 1.25 166 388 297 471 413 717 589 798 1.15 153 361 273 440 380 674 542 754 1.05 139 333 250 408 347 629 495 708 0.95 126 304 226 375 314 582 448 659 0.85 113 275 202 341 281 532 400 607 0.75 100 245 178 306 248 481 353 552 0.65 86 215 155 270 215 427 306 493 0.55 73 183 131 232 182 370 259 431 0.45 60 152 107 193 149 310 212 364 0.35 46 119 83 153 116 248 165 293 0.25 33 86 59 111 83 182 118 217 0.15 20 52 36 68 50 112 71 135 0.05 7 18 12 23 17 38 24 47 to provide on-orbit pointing vectors for SeaWiFS and Sea- Star. Pointing knowledge is a system level function. Verification of pointing knowledge will be made using measurements of land targets on orbit. Verification of a sufficient set of downlinked data must wait for the Pre-Ship Review of the SeaStar spacecraft. 21. STABILITY & REPEATABILITY at equal radiance levels, but separated by any time period up to two weeks. This includes the effects of perturbations at the orbital period. This stability requirement shall also be met for short-term temperature excursions that may be expected to occur during sunlit portions of the orbit. Data from lunar views, corrected for secular changes in lunar radiance exitance,collectedon severalconsecutive orbitswhile the moon isnear fullphase, shallbe provided with sufficientfrequencyto assessshort term and longterm Bias errors willbe removed from thedata duringground stability. processing in order to improve radiometric accuracy. To accomplish this,the sensor data must be stableover time, 21.2 Compliance as defined below. 21.1 Short-Term Stability Requirement Short-term stability applies to time intervals less than two weeks. This stability also applies to radiometric responses corrected on the ground using calibration data. The mean radiometric response of each spectral band, shall not differ by more than ±1% from another response measurement made while viewing the same source operating 28 Due to the short period between the completion of instrument modification and the Pre-Ship Review, it was not possible to test this specification before launch. The requirements will require examination of measurements on orbit. However, the radiometric calibration equations for the SeaWiFS bands (Barnes et al. 1994) contain factors, such as the temperature dependences for their radiometric sensitivities, which will be applied on orbit. Lunar measurements (Woodward et al. 1993) are also planned for

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R.A.Barnes,W.L.Barnes,W.E.Esaias,andC.R.McClain eachmeasurementopportunity.Thesemeasurements are eliminated the period of time for extended testing by the planned for twice each month, as the moon reaches 96% of full before and after each full phase. The correction for temperature dependence will also be applied to lunar measurements. 21.3 Long-Term Stability Requirement Long-term stability applies to time intervals between two weeks and 5 years. The mean corrected and calibrated radiometric response of each spectral band shall not change by more than ±2% over these time intervals. Compliance will be demonstrated by an estimate based upon shortterm tests plus analysis. 21.4 Compliance As shown in Table 1, the SeaWiFS instrument was completed (after stray light modifications) on 22 November 1993. The post modification Pre-Ship Review was held ten days later on 2 December, which was an insufficient interval of time to test long-term stability. However, measurements by the instrument before its modification to ameliorate the effects of stray light indicated radiometric stability from the instrument at the 1% level over a few months. In addition, solar measurements during "field tests" of the instrument (Section 18) have shown a consistency in the instrument's measurements at the 2-3% level from March to November 1993. These tests suggest, but do not guarantee, long term stability on orbit. Long-term stability during the SeaWiFS mission will be monitored, and instrument changes will be corrected, through a series of lunar, solar, and ground based measurements (McClain et al. 1992 and Woodward et al. 1993) 21.5 Band-to-Band Stability Requirement The relative amplitude stability between all pairs of spectral bands shall be better than ±0.5% measured at full-scale, and ±1% at half-scale. Each band shall be exposed to a source, and the mean calibrated responses determined. To compare outputs between bands, the ratio of the means shall be calculated for each band with respect to a common band. In addition, ratios shall be calculated for selected pairs of bands, which will be used in common retrieval algorithms. These ratios shall remain constant, within ±0.5% at full-scale and ±1% at half scale, over times separated by any interval up to two weeks. to make both lunar and solar diffuser measurements. There 21.6 Compliance manufacturer. However, the anecdotal information in Section 21.4 indicates that the performance of the instrument is at the level required by this specification. 22. IN-FLIGHT DATA 22.1 Requirement Data for calibration and stability monitoring shall be obtained from direct lunar views when the moon is greater than 80% full phase, and either an onboard stabilized source viewed by all optical elements or a solar diffuser. The sources shall fill the optical aperture of the sensor. These data shall be obtained for all channels with a SNR no less than 10% of the SNR values specified in Section 10, and shall measure changes in gain or throughput of the optical, focal plane, and electronic subsystems, using either onboard, lunar, or solar sources. In-flight radiometric characterization, i.e., output digital value versus input spectral radiance, shall be made with sufficient accuracy to assure that the calibration and stability requirements delineated in this specification are achieved. 22.1.1 Lunar Calibration Provision shall be made to use the moon at near full phase as a target source for monitoring stability. The lowest (least sensitive) gain shall accommodate direct viewing at near full lunar phase without saturation in any band. 22.1.2 Solar Diffuser If a solar illuminated diffuser is selected, data on the diffuser characteristics shall be provided which, when combined with data from other calibration systems, will be adequate to maintain knowledge of the calibration and stability of the radiometric data to within stated specifications throughout the five-year mission lifetime. 22.1.3 Internal Source In-flight data on characteristics of onboard sources, to show performance within the specifications, are required (should that approach be taken). 22.2 Compliance The SeaWiFS radiometer has been specifically designed are no internal sources within the instrument. As discussed in Section 15.2, there are gains for each SeaWiFS band As discussed in Sections 21.2 and 21.4 above, the time specifically set for the expected on-orbit solar and lunar period between the completion of the SeaWiFS instrument radiances. Also, as discussed extensively in the SeaWiFS and the Pre-Ship Review was less than two weeks. This Technical Report Series (McClain et al. 1992, Woodward short time period was instituted in an effort to help ensure et al. 1993, and Barnes et al. 1994) and Biggar et al. 1993, the launch of SeaWiFS and SeaStar at the earliest possible lunar and solar diffuser measurements form a fundamental date. The practical requirements for an early launch have part of SeaWiFS on-orbit calibrations. 29

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Prelaunch Acceptance Report 23. SUMMARY This technical memorandum contains only a portion of the information from the prelaunch characterization and calibration of the SeaWiFS radiometer. The SCADP is much more extensive. However, as discussed in this acceptance report, the requirements of the SeaWiFS specifications have determined the design of the instrument. Compliance with these specifications has defined the fundamental operation of SeaWiFS. This report summarizes prelaunch analyses that have been made by the review group, who are the co-authors of this technical memorandum. The review group concludes that, in the period between the delivery and the launch of the instrument, the SeaWiFS radiometer meets or exceeds all applicable specifications. Within the restriction that the instrument has not yet flown, SeaWiFS is found to be acceptable. However, the complete set of the information necessary for the acceptance, or rejection, of SeaWiFS and SeaStar is not yet available. There must be an extensive analysis of the on-orbit operational characteristics of SeaWiFS before a final judgement about the acceptability of the ocean color data set obtained by SeaWiFS can be made. The completion of this work will require information from 60 days of on-orbit operation by the satellite and its instrument. GLOSSARY A/D Analog-to-Digital BTR Bright Target Recovery DC Direct Current FWHM Fhll-Width at Half-Maximum GAC Global Area Coverage GSFC Goddard Space Flight Center HN (Polaroid) Not an acronym; a linear sheet polarizer used to check the polarization sensitivity of bands 7 and 8. HR (Polaroid) Not an acronym; a linear sheet polarizer used to check the polarizationsensitivityof bands 1-6. IFOV InstantaneousField-Of-View IR Infrared. LAC Local Area Coverage MTF Modulation TransferFunction NASA NationalAeronauticsand Space Administration NEdL Noise EquivalentDifferentialSpectralRadiance NIST NationalInstituteofStandardsand Technology OCDM Ocean Color Data Mission OSC OrbitalSciencesCorporation 3O for the SeaWiFS Radiometer SBRC Santa Barbara ResearchCenter SCADP SeaWiFS Calibrationand AcceptanceData Package SeaWiFS Sea-viewingWide Field-of-viewSensor SNR Signal-to-NoiseRatio TDI Time Delay and Integration SYMBOLS bl(k) Input data for polarization calculations for SeaWiFS band 1. b7(k) Input data for polarization calculations for SeaWiFS band 7. G Gain factor. G_ Gain factor at gain setting n. h(k) Residual values without the calculated sinusoidal response. Recorded maximum instrumentoutput in response to linearlypolarizedlight. Im_ Recorded minimum instrumentoutput in response to linearlypolarizedlight. LcloudMaximum radiancefrom reflectedlightoffofclouds. Lmax Maximum saturationradiance. ntypical Expected radiancefrom the ocean measured on orbit. n Gain setting. PF Polarizationfactor. Si Initialdetectorsignal. S,_ Detectorsignalwith gain. x Abscissaor longitudinalcoordinate,or the pixel number withina scan linedependingon usage. y Ordinateor meridionalcoordinate. z Mantissacoordinate. a One standarddeviation. REFERENCES Barnes,R.A.,and A. Holmes, 1993:Overview ofthe SeaWiFS Ocean Sensor. Proc. SPIE, 1,939, 224-232. Barnes, R.A., A. Holmes, W.L. Barnes, W.E. Esaias, and C.R. McClain, 1994: The SeaWiFS Prelaunch Radiometric Calibration and Spectral Characterization, NASA Tech. Memo. 10_566, Vol. 23 S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, (in press). Biggar, S.F., P. Slater, K. Thome, A. Holmes, and R. Barnes, 1993: Preflight solar-based calibration of SeaWiFS, Proc. SPIE, 1,939, 233-242. McClain, C.R., W.E. Esaias, W.L. Barnes, B. Guenther, D. Endres, S.B. Hooker, B. Mitchell, and R.A. Barnes, 1992: SeaWiFS Calibration and Validation Plan, NASA Tech. Memo. 10._566, Vol. 3, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 41 pp.

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R.A. Barnes, W.L. Barnes, W.E. Esaias, and C.R. McClain Walker, J.H., C. Cromer, and J. McLean, 1991: A technique for improving the calibration of large-area sphere sources. Proc. SPIE, 1,493, 224-230. Woodward, R.H., R.A. Barnes, C.R. McClaln, W.E. Esaias, W.L. Barnes, and A.T. Mecherikurmel, 1993: Modeling of the SeaWiFS Solar and Lunar Observations. NASA Tech. Memo. 104566, Vol. 10, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 26 pp. THE SEAWIFS TECHNICAL REPORT SERIES Vol. I Hooker, S.B., W.E. Esalas, G.C. Feldman, W.W. Gregg, and C.R. McClain, 1992: An Overview of SeaWiFS and Ocean Color. NASA Tech. Memo. 104566, Vol. 1, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 24 pp., plus color plates. Vol. 2 Gregg, W.W., 1992: Analysis of Orbit Selection for SeaWiFS: Ascending vs. Descending Node. NASA Tech. Memo. 104566, Vol. P, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 16 pp. Vol. 3 McClaln, C.R., W.E. Esaias, W. Barnes, B. Guenther, D. Endres, S. Hooker, G. Mitchell, and R. Barnes, 1992: Calibration and Validation Plan for SeaWiFS. NASA Tech. Memo. 104566, Vol. 3, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 41 pp. Vol. 4 McClain, C.R., E. Yeh, and G. Fu, 1992: An Analysis of GAC Sampling Algorithms: A Case Study. NASA Tech. Memo. 104566, Vol. 4, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 22pp., plus color plates. Vol. 5 Mueller, J.L., and R.W. Austin, 1992: Ocean Optics Protocols for SeaWiFS Validation. NASA Tech. Memo. 10._566, Vol. 5, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 43 pp. Vol. 6 Firestone, E.R., and S.B. Hooker, 1992: SeaWiFS Technical Report Series Summary Index: Volumes 1-5. NASA Tech. Memo. 104566, Vol. 6, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 9 pp. Vol. 7 Darzi, M., 1992: Cloud Screening for Polar Orbiting Visible and IR Satellite Sensors. NASA Tech. Memo. 104566, Vol. 7, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 7 pp. Vol. 8 Hooker, S.B., W.E. Esaias, and L.A. Rexrode, 1993: Proceedings of the First SeaWiFS Science Team Meeting. NASA Tech. Memo. I04566, Vol. 8, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 61 pp. Vol. 9 Gregg, W.W., F.C. Chen, A.L. Mezaaclhe, J.D. Chen, J.A. Whiting, 1993: The Simulated SeaWiFS Data Set, Version 1. NASA Tech. Memo. 104566, Vol. 9, S.B. Hooker, E.R. Firestone, and A.W. Indest, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 17 pp. Vol. 10 Woodward, R.H., R.A. Barnes, C.R. McClain, W.E. Esaias, W.L. Barnes, and A.T. Mecherikunnel, 1993: Modeling of the SeaWiFS Solar and Lunar Observations. NASA Tech. Memo. 104566, Vol. 10, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 26 pp. Vol. 11 Patt, F.S., C.M. Hoisington, W.W. Gregg, and P.L. Coronado, 1993: Analysis of Selected Orbit Propagation Models for the SeaWiFS Mission. NASA Tech. Memo. 104566, Vol. 11, S.B. Hooker, E.R. Firestone, and A.W. Indest, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 16 pp. Vol. 12 Firestone, E.R., and S.B. Hooker, 1993: SeaWiFS Technical Report Series Summary Index: Volumes 1-11. NASA Tech. Memo. 104566, Vol. 1P, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 28 pp. Vol. 13 McClain, C.R., K.R. Arrigo, J. Comiso, R. Fraser, M. Darzi, J.K. Firestone, B. Schieber, E-n. Yeh, and C.W. Sullivan, 1994: Case Studies for SeaWiFS Calibration and Validation, Part 1. NASA Tech. Memo. 104566, Vol. 13, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 52pp., plus color plates. I/ol. 14 Mueller, J.L., 1993: The First SeaWiFS Intercalibration Round- Robin Experiment, SIRREX-1, July 1992. NASA Tech. Memo. 104566, Vol. 14, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 60pp. Vol. 15 Gregg, W.W., F.S. Part, and R.H. Woodward, 1994: The Simulated SeaWiFS Data Set, Version 2. NASA Tech. Memo. 104566, Vol. 15, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 42pp., plus color plates. Vol. 16 Mueller, J.L., B.C. Johnson, C.L. Cromer, J.W. Cooper, J.T. McLean, S.B. Hooker, and T.L. Westphal, 1994: The Second SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-2, June 1993. NASA Tech. Memo. 104566, Vol. 16, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 121 pp. Vol. 17 Abbott, M.R., O.B. Brown, H.R. Gordon, K.L. Carder, R.E. Evans, F.E. Muller-Karger, and W.E. Esaias, 1994: Ocean Color in the 21st Century: A Strategy for a 20-Year Time Series. NASA Tech. Memo. 104566, Vol. 17, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 20 pp. 31

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PrelaunchAcceptanceReportforthe SeaWiFSRadiometer Vol. 18 Firestone, E.R., and S.B. Hooker, 1994: SeaWiFS Technical Report Series Summary Index: Volumes 1-17. NASA Tech. Memo. 104566, Vol. 18, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, (in press). Vol. 19 McClain, C.R., R.S. Fraaer, J.T. McLean, M. Darzi, J.K. Firestone, F.S. Patt, B.D. Schieber, R.H. Woodward, E-n. Yeh, S. Mattoo, S.F. Biggar, P.N. Slater, K.J. Thome, A.W. Holmes, R.A. Barnes, and K.J. Vow, 1994: Cese Studies for SeaWiFS Calibration and Validation, Part 2. NASA Tech. Memo. 10._566, Vol. 19, S.B. Hooker, E.R. Firestone, and J.G. Acker, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 73 pp. Vol. 20 Hooker, S.B., C.R. McClain, J.K. Firestone, T.L. Westphal, E-n. Yeh, and Y. Ge, 1994: The SenWiFS Bio-Optical Archive and Storage System (SeaBASS), Part 1. NASA Tech. Memo. 10.4566, Vol. _0, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 40 pp. 32 Vol. 21 Acker, J.G., 1994: The Heritage of SeaWiFS: A Retrospective on the CZCS NIMBUS Experiment Team (NET) Program. NASA Tech. Memo. 10._566, Vol. _1, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, (in press). Vol. 22 Barnes, R.A., W.L. Barnes, W.E. Esaias, and C.R. McClain, 1994: Prehtmch Acceptance Report for the SeaWiFS Radiometer. NASA Tech. Memo. 104566, Vol. _2, S.B. Hooker, E.R. Firestone, and J.G. Acker, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 32 pp.

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REPORT DOCUMENTATION PAGE oM8No.o7o4.o188 I Form Approved Public redorling burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information, Send comments regarding this burden estimate or any other aspect of this colkJctio_ of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports. 1215 Jefferson Davis Highway, Suits 1204, Ad_on, VA 9_9¢-4302, and to the Office of Management and Bud<jet, Paperwork Reduction Proiect 10704-01881. Washington, DC 20503, 1. AGENCY USE ONLY (Leave blank) 2. REPORTDATE September 1994 4. TITLE AND SUBTITLE SeaWiFS Technical Report Series Volume 22 Prelaunch Acceptance Report for the SeaWiFS 6. AUTHOR(S) Robert A. Barnes, W'dliam L Barnes, Wayne E. Esaias and Charles R. M Series Editor: Stanford B. Hooker and Elaine IL Fn'estone Technical Editor. James G. Acker 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Laboratory for Hydrospheric Processes Goddard Space Flight Center Greenbelt, Maryland 20771 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) National Aeronautics and Space Administration Washington, D.C. 20546-0001 11. SUPPLEMENTARY NOTES Robert A. Barnes: ManTech, Inc., Wallops Island, Virginia; Maryland; and James G. Acker: Hughes STX, Lanham, Maryland 12a. DiSTRIBU'RON/AVAILABILrrY STATEMENT Unclassified-Unlimited Subject Category 48 3. REPORT TYPE AND DA_S COVERED Technical Memorandum 5. FUNDING NUMBERS Radiometer 970.2 8. PERFORMING ORGANIZATION REPORT NUMBER 94B00126 10. SPONSORING/MONITORING AGENCY REPORT NUMBER TM-104566, Vol. 22 Elaine R. Firestone: General Sciences Corporation, Laurel, 12b. B_rHIBUTION CODE Report is available from the NASA Center for AeroSpace Information, 800 Elkridge Landing Road, Linthicum Heights, MD 21090; (301) 621-0390. 13. ABSTRACT (Max_ 200 wot_s) The final Eceptance, or rejection, of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) will be determined by the instrument's on-orbit operation. There is, however, an extensive set of laboratory measurements describing the operating characteristics of the radiometer. Many of the requirements in the Ocean Color Data Mission (OCDM) specifications can be checked only by laboratory measurements. Here_ the calibration review panel (composed of the authors of this technical memorandum) examines the lalxxat(xy chamcte_on and calitxation of SeaW'LPS in the light of the OCDM performance SlX_ificalion. Overall, the performance of the SeaWLPS insmmaent meets or exceeds the requirements of the OCDM contract in all but a few unimportant details. The detailed results of this examination are presented here by following the outline of the specifications, as found in the ContracL The results are presented in the form of requirements and compliance pairs. These results give conclusions on many, but not all, of the performance specifications. The acceptance by this panel of the performance of SeaWiFS must only be considered as an intermediate conclusion. The ultimate acceptance (or rejection) of the SeaW'tFS data set will rely on the measurements made by the insmmaent on orbit. 14. SUBJECT TERMS 15. NUMBER OF PAGES 32 SeaWiFS, Oceanography, Acceptance, Radiometer, Dark Level, Fore-and-Aft Pointing Requirement, Compliance, Polarization, Pointing Knowledge 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION OF REPORT OF THIS PAGE Unclassified Unclassified NSN 7540-01-280-5500 16. PRICE CODE 19. SECURITY CLASSiRCATION 20. UMITATION OF ABSTRACT OF ABSTRACT Unclassified •Unlimited Standard Form 298 (Rev. 2-89) I_rescrlbed by ANSI bid. 239-18, 298-102

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