Abstract

We assessed the geometric and radiometric performance of the ocean color and temperature scanner (OCTS) using data acquired over the United States. Initial results indicated a geometric offset in the along-track direction of 4–5 pixels that was attributed to a tilt bias. OCTS radiometric data appeared to suffer from near-field and possibly far-field scatter effects. Analysis of radiometric stability was inconclusive because of daily variability and the absence of a full seasonal cycle. Comparison of OCTS-computed water-leaving radiances with colocated in situ measurements showed that the prelaunch calibration required adjustment from -2% to +13%. Minor modification of OCTS data processing based on these results and avoidance of near-field scatter effects can enable improved and more-reliable OCTS data for quantitative scientific analyses.

© 1999 Optical Society of America

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References

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  1. W. W. Gregg, “Initial analysis of ocean color data from the ocean color and temperature scanner. I. Imagery analysis,” Appl. Opt. 38, 476–485 (1999).
    [CrossRef]
  2. M. Shimada, H. Oaku, Y. Mitomi, A. Mukaida, “OCTS program report: OCTS Cal/Val,” Proceedings of the Second ADEOS Symposium Workshop (National Space Development Agency, Tokyo, Japan, 1997), pp. 139–161.
  3. National Space Development Agency, “ADEOS to ground station interface document,” (NASDA Earth Observation Research Center, Tokyo, Japan, 1997), Version 1.3.2.
  4. F. S. Patt, W. W. Gregg, “Exact, closed form geolocation algorithm for Earth survey sensors,” Int. J. Remote Sens. 15, 3719–3734 (1994).
    [CrossRef]
  5. F. S. Patt, R. H. Woodward, W. W. Gregg, “Automated navigation assessment for Earth survey sensors using island targets,” Int. J. Remote Sens. 18, 3311–3336 (1997).
    [CrossRef]
  6. M. Wang, Goddard Space Flight Center, Code 970.2, Greenbelt, Md. 20771 (personal communication, September1998).
  7. R. O. Green, Jet Propulsion Laboratory, Pasadena, Calif. 91109 (personal communication, May1997).
  8. H. R. Gordon, University of Miami, Coral Gables, Fla. 33124 (personal communication, July1997).
  9. H. R. Gordon, M. Wang, “Retrieval of water-leaving radiance and aerosol optical thickness over the oceans with SeaWiFS: a preliminary algorithm,” Appl. Opt. 33, 443–452 (1994).
    [CrossRef] [PubMed]
  10. H. R. Gordon, J. W. Brown, R. H. Evans, “Exact Rayleigh scattering calculations for use with the Nimbus-7 coastal zone color scanner,” Appl. Opt. 27, 862–871 (1988).
    [CrossRef] [PubMed]
  11. H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
    [CrossRef]
  12. R. M. Pope, E. S. Fry, “Absorption spectrum (380–700 nm) of pure water. II. Integrating cavity measurements,” Appl. Opt. 36, 8710–8723 (1997).
    [CrossRef]
  13. R. H. Evans, H. R. Gordon, “Coastal Zone Color Scanner system calibration: a retrospective examination,” J. Geophys. Res. 99, 7293–7307 (1994).
    [CrossRef]
  14. H. R. Gordon, D. K. Clark, J. W. Brown, O. B. Brown, R. H. Evans, W. W. Broenkow, “Phytoplankton pigment concentrations in the Middle Atlantic Bight: comparison of ship determinations and CZCS estimates,” Appl. Opt. 22, 20–36 (1983).
    [CrossRef] [PubMed]
  15. K. Arai, H. Fukushima, “Stray light effect found in ADEOS ocean color and temperature scanner (OCTS) data: description of the problem and its effect on estimated chlorophyll-a concentration,” presented at Ocean Optics XIV Meeting, Kailua-Kona, Hawaii, November 1998.
  16. H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
    [CrossRef]
  17. M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
    [CrossRef]

1999 (1)

1998 (2)

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

1997 (2)

R. M. Pope, E. S. Fry, “Absorption spectrum (380–700 nm) of pure water. II. Integrating cavity measurements,” Appl. Opt. 36, 8710–8723 (1997).
[CrossRef]

F. S. Patt, R. H. Woodward, W. W. Gregg, “Automated navigation assessment for Earth survey sensors using island targets,” Int. J. Remote Sens. 18, 3311–3336 (1997).
[CrossRef]

1994 (3)

H. R. Gordon, M. Wang, “Retrieval of water-leaving radiance and aerosol optical thickness over the oceans with SeaWiFS: a preliminary algorithm,” Appl. Opt. 33, 443–452 (1994).
[CrossRef] [PubMed]

R. H. Evans, H. R. Gordon, “Coastal Zone Color Scanner system calibration: a retrospective examination,” J. Geophys. Res. 99, 7293–7307 (1994).
[CrossRef]

F. S. Patt, W. W. Gregg, “Exact, closed form geolocation algorithm for Earth survey sensors,” Int. J. Remote Sens. 15, 3719–3734 (1994).
[CrossRef]

1988 (2)

H. R. Gordon, J. W. Brown, R. H. Evans, “Exact Rayleigh scattering calculations for use with the Nimbus-7 coastal zone color scanner,” Appl. Opt. 27, 862–871 (1988).
[CrossRef] [PubMed]

H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
[CrossRef]

1983 (1)

Arai, K.

K. Arai, H. Fukushima, “Stray light effect found in ADEOS ocean color and temperature scanner (OCTS) data: description of the problem and its effect on estimated chlorophyll-a concentration,” presented at Ocean Optics XIV Meeting, Kailua-Kona, Hawaii, November 1998.

Baker, K. S.

H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
[CrossRef]

Broenkow, W. W.

Brown, J. W.

Brown, O. B.

H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
[CrossRef]

H. R. Gordon, D. K. Clark, J. W. Brown, O. B. Brown, R. H. Evans, W. W. Broenkow, “Phytoplankton pigment concentrations in the Middle Atlantic Bight: comparison of ship determinations and CZCS estimates,” Appl. Opt. 22, 20–36 (1983).
[CrossRef] [PubMed]

Clark, D. K.

H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
[CrossRef]

H. R. Gordon, D. K. Clark, J. W. Brown, O. B. Brown, R. H. Evans, W. W. Broenkow, “Phytoplankton pigment concentrations in the Middle Atlantic Bight: comparison of ship determinations and CZCS estimates,” Appl. Opt. 22, 20–36 (1983).
[CrossRef] [PubMed]

Evans, R. H.

R. H. Evans, H. R. Gordon, “Coastal Zone Color Scanner system calibration: a retrospective examination,” J. Geophys. Res. 99, 7293–7307 (1994).
[CrossRef]

H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
[CrossRef]

H. R. Gordon, J. W. Brown, R. H. Evans, “Exact Rayleigh scattering calculations for use with the Nimbus-7 coastal zone color scanner,” Appl. Opt. 27, 862–871 (1988).
[CrossRef] [PubMed]

H. R. Gordon, D. K. Clark, J. W. Brown, O. B. Brown, R. H. Evans, W. W. Broenkow, “Phytoplankton pigment concentrations in the Middle Atlantic Bight: comparison of ship determinations and CZCS estimates,” Appl. Opt. 22, 20–36 (1983).
[CrossRef] [PubMed]

Fry, E. S.

Fukushima, H.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

K. Arai, H. Fukushima, “Stray light effect found in ADEOS ocean color and temperature scanner (OCTS) data: description of the problem and its effect on estimated chlorophyll-a concentration,” presented at Ocean Optics XIV Meeting, Kailua-Kona, Hawaii, November 1998.

Gordon, H. R.

Green, R. O.

R. O. Green, Jet Propulsion Laboratory, Pasadena, Calif. 91109 (personal communication, May1997).

Gregg, W. W.

W. W. Gregg, “Initial analysis of ocean color data from the ocean color and temperature scanner. I. Imagery analysis,” Appl. Opt. 38, 476–485 (1999).
[CrossRef]

F. S. Patt, R. H. Woodward, W. W. Gregg, “Automated navigation assessment for Earth survey sensors using island targets,” Int. J. Remote Sens. 18, 3311–3336 (1997).
[CrossRef]

F. S. Patt, W. W. Gregg, “Exact, closed form geolocation algorithm for Earth survey sensors,” Int. J. Remote Sens. 15, 3719–3734 (1994).
[CrossRef]

Higurashi, A.

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

Ishizaka, J.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

Kawamura, H.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

Kishino, M.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

Mitomi, Y.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

M. Shimada, H. Oaku, Y. Mitomi, A. Mukaida, “OCTS program report: OCTS Cal/Val,” Proceedings of the Second ADEOS Symposium Workshop (National Space Development Agency, Tokyo, Japan, 1997), pp. 139–161.

Mukaida, A.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

M. Shimada, H. Oaku, Y. Mitomi, A. Mukaida, “OCTS program report: OCTS Cal/Val,” Proceedings of the Second ADEOS Symposium Workshop (National Space Development Agency, Tokyo, Japan, 1997), pp. 139–161.

Murakami, H.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

Nakajima, T.

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

Nakamura, Y.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

Noguchi, T.

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

Oaku, H.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

M. Shimada, H. Oaku, Y. Mitomi, A. Mukaida, “OCTS program report: OCTS Cal/Val,” Proceedings of the Second ADEOS Symposium Workshop (National Space Development Agency, Tokyo, Japan, 1997), pp. 139–161.

Patt, F. S.

F. S. Patt, R. H. Woodward, W. W. Gregg, “Automated navigation assessment for Earth survey sensors using island targets,” Int. J. Remote Sens. 18, 3311–3336 (1997).
[CrossRef]

F. S. Patt, W. W. Gregg, “Exact, closed form geolocation algorithm for Earth survey sensors,” Int. J. Remote Sens. 15, 3719–3734 (1994).
[CrossRef]

Pope, R. M.

Shimada, M.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

M. Shimada, H. Oaku, Y. Mitomi, A. Mukaida, “OCTS program report: OCTS Cal/Val,” Proceedings of the Second ADEOS Symposium Workshop (National Space Development Agency, Tokyo, Japan, 1997), pp. 139–161.

Smith, R. C.

H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
[CrossRef]

Tanaka, T.

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

Toratini, M.

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

Wang, M.

Woodward, R. H.

F. S. Patt, R. H. Woodward, W. W. Gregg, “Automated navigation assessment for Earth survey sensors using island targets,” Int. J. Remote Sens. 18, 3311–3336 (1997).
[CrossRef]

Appl. Opt. (5)

Int. J. Remote Sens. (2)

F. S. Patt, W. W. Gregg, “Exact, closed form geolocation algorithm for Earth survey sensors,” Int. J. Remote Sens. 15, 3719–3734 (1994).
[CrossRef]

F. S. Patt, R. H. Woodward, W. W. Gregg, “Automated navigation assessment for Earth survey sensors using island targets,” Int. J. Remote Sens. 18, 3311–3336 (1997).
[CrossRef]

J. Geophys. Res. (2)

H. R. Gordon, O. B. Brown, R. H. Evans, J. W. Brown, R. C. Smith, K. S. Baker, D. K. Clark, “A semianalytic radiance model of ocean color,” J. Geophys. Res. 93, 10,909–10,924 (1988).
[CrossRef]

R. H. Evans, H. R. Gordon, “Coastal Zone Color Scanner system calibration: a retrospective examination,” J. Geophys. Res. 99, 7293–7307 (1994).
[CrossRef]

J. Oceanogr. (2)

H. Fukushima, A. Higurashi, Y. Mitomi, T. Nakajima, T. Noguchi, T. Tanaka, M. Toratini, “Correction of atmospheric effect on ADEOS/OCTS ocean color data: algorithm description and evaluation of performance,” J. Oceanogr. 54, 417–430 (1998).
[CrossRef]

M. Shimada, H. Oaku, Y. Mitomi, H. Murakami, A. Mukaida, Y. Nakamura, J. Ishizaka, H. Kawamura, T. Tanaka, M. Kishino, H. Fukushima, “Calibration and validation of the ocean color version 3 product from the ADEOS OCTS,” J. Oceanogr. 54, 401–416 (1998).
[CrossRef]

Other (6)

K. Arai, H. Fukushima, “Stray light effect found in ADEOS ocean color and temperature scanner (OCTS) data: description of the problem and its effect on estimated chlorophyll-a concentration,” presented at Ocean Optics XIV Meeting, Kailua-Kona, Hawaii, November 1998.

M. Shimada, H. Oaku, Y. Mitomi, A. Mukaida, “OCTS program report: OCTS Cal/Val,” Proceedings of the Second ADEOS Symposium Workshop (National Space Development Agency, Tokyo, Japan, 1997), pp. 139–161.

National Space Development Agency, “ADEOS to ground station interface document,” (NASDA Earth Observation Research Center, Tokyo, Japan, 1997), Version 1.3.2.

M. Wang, Goddard Space Flight Center, Code 970.2, Greenbelt, Md. 20771 (personal communication, September1998).

R. O. Green, Jet Propulsion Laboratory, Pasadena, Calif. 91109 (personal communication, May1997).

H. R. Gordon, University of Miami, Coral Gables, Fla. 33124 (personal communication, July1997).

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Figures (9)

Fig. 1
Fig. 1

OCTS image from 11 June 1997 showing the along-track offset detected in uncorrected imagery and results from adjusting the tilt. (a) Image of L t (865) (prelaunch calibration) indicates a significant departure of land features in the U.S. East Coast from an overlying coastline. Note particularly the departures in the Delaware Bay and Long Island, New York. (b) Image of the cloud–land–water discriminator function, showing the effects of adjusting the tilt, producing a better match of land features to the coastline. Note the ability of the discriminator function to distinguish the three Earth types, even when clouds overlay land or ocean.

Fig. 2
Fig. 2

Rayleigh-corrected reflectance in band 8 (865 nm), which represents the aerosol reflectance ρ a (865) showing the response of OCTS to bright targets, in this case, clouds. This image is from 29 January 1997 and is located in the Sargasso Sea east of the Bahamas Islands. Large reflectances can be seen bordering the large cloud bank stretching southwest to northeast in the image and around the medium to large isolated clouds—particularly one located at the southwestern edge oriented nearly north–south (at the lower left-hand portion of the figure) and one at the northeastern edge of the scene. The scan edge is apparent in the lower right of the figure.

Fig. 3
Fig. 3

As in Fig. 2 but illustrating the effects of reflectance ratios, in this case, the ratio of band 6 to band 8 [also defined as ε(670,865)]. The two isolated clouds discussed in Fig. 2 show enhancement of the ratio on the western side and darkening on the eastern side, producing a shadow.

Fig. 4
Fig. 4

Transect through the north–south-oriented cloud in the lower left of Figs. 2 and 3 quantifies the apparent effects of bright targets on OCTS. The reflectance ratio of band 6 to band 8 increases as the scan approaches the cloud from the west, producing an elevated ratio to approximately 1.0 from a background value of 0.6 (these data utilize the prelaunch calibration of OCTS and are not expected to produce a realistic ratio). A depression following the cloud produces the shadow that is apparent in the image. These band 6 and 8 effects are due to different spectral responses of OCTS to bright targets because of the placement of the bands on the focal plane. Band 6 has a nearly symmetric response on both sides of the cloud because it is nearly on the optical axis. Band 8 exhibits a pronounced lingering effect on the east side of the cloud. The combination of these two effects produces the brightening and darkening effects seen in Fig. 3 when taken as a ratio. Bands 4 and 5 are at opposite ends of the focal plane and exhibit expected behavior given their relative positions. Band 5 Rayleigh-corrected reflectance has been increased by 0.0057 to emphasize its effects relative to band 4. Note that the major effects of near-field scatter are limited to approximately 30 pixels.

Fig. 5
Fig. 5

OCTS focal plane orientation.

Fig. 6
Fig. 6

OCTS image of Florida and the eastern Gulf of Mexico on 24 January 1997. Top: band 8 aerosol reflectance. Bottom: reflectance ratio of band 6 to band 8. The cloud bank in the northern Gulf of Mexico produces bright target effects discussed in the text, but also appear to exhibit effects exceeding the 30 × 10 pixel dimensions of the focal plane. This may be due to far-field scatter, which is less intense than near-field scatter but may affect observations at quite large distances from bright targets. A key feature of far-field scatter is its nonspectral nature. A concurrent view of the reflectance ratio shows no apparent effects from the cloud feature, suggesting spectral independence.

Fig. 7
Fig. 7

South-to-north transect through the center of the gap in the northeastern Gulf of Mexico in Fig. 6 shows little variation in the aerosol reflectance ratio of band 6:band 8 and nearly identical slopes in their reflectances. Near-field effects appear to last approximately 20–30 pixels in the along-track direction, and the long sloping tail extending over 100 pixels from the bright target may indicate far-field scatter.

Fig. 8
Fig. 8

Time series of median and IQR of OCTS Rayleigh-corrected reflectances for the Gulf of Mexico for the life of the mission. Substantial daily variability is apparent, which obscures the detection of a longer-term trend. The ratio of band 7 (765 nm) to 8 (865 nm) appears to be stable (top), at least to the best that we can determine under the high daily variability, and band 6 (670 nm) appears to be slightly increasing, as inferred from the plots of ratios 6:8, 6:7, and 5:6. Bands 4 (520 nm) and 5 (565 nm) appear to be stable. Percent changes computed over the life of the mission based on a linear best fit were 0.08%, 3.06%, 2.90%, -8.2%, and -0.23%, respectively, from top to bottom.

Fig. 9
Fig. 9

Time series of median and IQR calibration adjustment factors computed for expected clear-water radiances in the Gulf of Mexico. Diamonds indicate actual in situ observations from 18 November 1996 in Hawaii to 9 June 1997 in the U.S. East Coast. Daily variability is apparent but is reduced relative to the Rayleigh-corrected reflectance ratios, most likely due to partial removal by atmospheric correction. Apparent seasonal variability can also be seen, and it diminishes with increasing wavelength. As with Rayleigh-corrected reflectance ratios, long-term trends are difficult to discern because of seasonal and daily variability. However, linear best-fit analysis produced the following long-term trends for the six bands: -2.0%, -1.80%, -1.21%, 0.48%, 0.45%, and -0.75% for the bands from top to bottom (bands 1–6).

Tables (4)

Tables Icon

Table 1 OCTS Ocean Color Spectral Characteristics a

Tables Icon

Table 2 Information about Measured in situ Water-Leaving Radiances Used to Evaluate the OCTS Calibrationa

Tables Icon

Table 3 Statistics for Geometric Adjustments for OCTS by use of Scan Edges (±300 pixels from usable edge) to Identify a Source of Geometric Biasa

Tables Icon

Table 4 Median and IQR Values for the Calibration Adjustment Factora

Equations (11)

Equations on this page are rendered with MathJax. Learn more.

D=Ltc443N+6Ltc865N-0.2Ltc670N,
3D8=land, D15 or LtλN1.5 mW cm-2 sr-1 μm-1=clouds, D<3=water.
ΔLwλN=LwiλN-LwsλN
LwsλN=Ltλ-Lrλ-Laλ-Lraλ/tλ, θtoλ, θocos θo,
t=exp-τr/2+τoz/cos θ
ΔLt=ΔLwλNtto cos θo.
F=Lts+ΔLt/Lts
F=1+ΔLt/Lts,
ρt-r=πLt-Lr/Fo cos θo,
Fo=FoE exp-τoz/cos θ+cos θo,
ε765,865=ρa765/ρa865.

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