Abstract

Atmospheric correction in ocean-color remote sensing corrects more than 90% of signals in the visible contributed from the atmosphere measured at satellite altitude. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) atmospheric correction uses radiances measured at two near-infrared wavelengths centered at 765 and 865 nm to estimate the atmospheric contribution and extrapolate it into the visible range. However, the SeaWiFS 765-nm band, which covers 745–785 nm, completely encompasses the oxygen A-band absorption. The O2 A-band absorption usually reduces more than 10–15% of the measured radiance at the SeaWiFS 765-nm band. Ding and Gordon [Appl. Opt. 34, 2068–2080 (1995)] proposed a numerical scheme to remove the O2 A-band absorption effects from the atmospheric correction. This scheme has been implemented in the SeaWiFS ocean-color imagery data-processing system. I present results that demonstrate a method to validate the SeaWiFS 765-nm O2 A-band absorption correction by analyzing the sensor-measured radiances at 765 and 865 nm taken looking at the clouds over the oceans. SeaWiFS is usually not saturated with cloudy scenes because of its bilinear gain design. Because the optical and radiative properties of water clouds are nearly independent of the wavelengths ranging from 400 to 865 nm, the sensor-measured radiances above the cloud at the two near-infrared wavelengths are comparable. The retrieved cloud optical thicknesses from the SeaWiFS band 7 measurements are compared for cases with and without the O2 A-band absorption corrections and from the band 8 measurements. The results show that, for air-mass values of 2–5, the current SeaWiFS O2 A-band absorption correction works reasonably well. The validation method is potentially applicable for in-orbit relative calibration for SeaWiFS and other satellite sensors.

© 1999 Optical Society of America

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References

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  1. S. B. Hooker, W. E. Esaias, G. C. Feldman, W. W. Gregg, C. R. McClain, An Overview of SeaWiFS and Ocean Color, Vol. 1 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1992).
  2. 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]
  3. H. R. Gordon, “Atmospheric correction of ocean color imagery in the Earth Observing System era,” J. Geophys. Res. 102, 17,081–17,106 (1997).
    [CrossRef]
  4. K. Ding, H. R. Gordon, “Analysis of the influence of O2A-band absorption on atmospheric correction of ocean color imagery,” Appl. Opt. 34, 2068–2080 (1995).
    [CrossRef] [PubMed]
  5. H. Yang, H. R. Gordon, “Remote sensing of ocean color: assessment of water-leaving radiance bidirectional effects on atmospheric diffuse transmittance,” Appl. Opt. 36, 7887–7897 (1997).
    [CrossRef]
  6. H. R. Gordon, M. Wang, “Influence of oceanic whitecaps on atmospheric correction of ocean-color sensor,” Appl. Opt. 33, 7754–7763 (1994).
    [CrossRef] [PubMed]
  7. R. S. Fraser, The Effect of Oxygen Absorption on Band-7 Radiance, Vol. 27 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).
  8. R. A. Barnes, A. W. Holmes, W. E. Esaias, Stray Light in the SeaWiFS Radiometer, Vol. 31 of SeaWiFS Tech. Rep. Series, NASA Tech. Memo. 104566 (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).
  9. S. Twomey, T. Cocks, “Spectral reflectance of clouds in the near-infrared: comparison of measurements and calculations,” J. Meteorol. Soc. Jpn. 60, 583–592 (1982).
  10. S. Twomey, T. Cocks, “Remote sensing of cloud parameters from spectral reflectance measurements in the near-infrared,” Beitr. Phys. Atmos. 62, 172–179 (1989).
  11. T. Nakajima, M. D. King, “Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. I. Theory,” J. Atmos. Sci. 47, 1878–1893 (1990).
    [CrossRef]
  12. M. Wang, M. D. King, “Correction of Rayleigh scattering effects in cloud optical thickness retrievals,” J. Geophys. Res. 102, 25,915–25,926 (1997).
    [CrossRef]

1997

H. R. Gordon, “Atmospheric correction of ocean color imagery in the Earth Observing System era,” J. Geophys. Res. 102, 17,081–17,106 (1997).
[CrossRef]

M. Wang, M. D. King, “Correction of Rayleigh scattering effects in cloud optical thickness retrievals,” J. Geophys. Res. 102, 25,915–25,926 (1997).
[CrossRef]

H. Yang, H. R. Gordon, “Remote sensing of ocean color: assessment of water-leaving radiance bidirectional effects on atmospheric diffuse transmittance,” Appl. Opt. 36, 7887–7897 (1997).
[CrossRef]

1995

1994

1990

T. Nakajima, M. D. King, “Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. I. Theory,” J. Atmos. Sci. 47, 1878–1893 (1990).
[CrossRef]

1989

S. Twomey, T. Cocks, “Remote sensing of cloud parameters from spectral reflectance measurements in the near-infrared,” Beitr. Phys. Atmos. 62, 172–179 (1989).

1982

S. Twomey, T. Cocks, “Spectral reflectance of clouds in the near-infrared: comparison of measurements and calculations,” J. Meteorol. Soc. Jpn. 60, 583–592 (1982).

Barnes, R. A.

R. A. Barnes, A. W. Holmes, W. E. Esaias, Stray Light in the SeaWiFS Radiometer, Vol. 31 of SeaWiFS Tech. Rep. Series, NASA Tech. Memo. 104566 (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).

Cocks, T.

S. Twomey, T. Cocks, “Remote sensing of cloud parameters from spectral reflectance measurements in the near-infrared,” Beitr. Phys. Atmos. 62, 172–179 (1989).

S. Twomey, T. Cocks, “Spectral reflectance of clouds in the near-infrared: comparison of measurements and calculations,” J. Meteorol. Soc. Jpn. 60, 583–592 (1982).

Ding, K.

Esaias, W. E.

R. A. Barnes, A. W. Holmes, W. E. Esaias, Stray Light in the SeaWiFS Radiometer, Vol. 31 of SeaWiFS Tech. Rep. Series, NASA Tech. Memo. 104566 (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).

S. B. Hooker, W. E. Esaias, G. C. Feldman, W. W. Gregg, C. R. McClain, An Overview of SeaWiFS and Ocean Color, Vol. 1 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1992).

Feldman, G. C.

S. B. Hooker, W. E. Esaias, G. C. Feldman, W. W. Gregg, C. R. McClain, An Overview of SeaWiFS and Ocean Color, Vol. 1 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1992).

Fraser, R. S.

R. S. Fraser, The Effect of Oxygen Absorption on Band-7 Radiance, Vol. 27 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).

Gordon, H. R.

Gregg, W. W.

S. B. Hooker, W. E. Esaias, G. C. Feldman, W. W. Gregg, C. R. McClain, An Overview of SeaWiFS and Ocean Color, Vol. 1 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1992).

Holmes, A. W.

R. A. Barnes, A. W. Holmes, W. E. Esaias, Stray Light in the SeaWiFS Radiometer, Vol. 31 of SeaWiFS Tech. Rep. Series, NASA Tech. Memo. 104566 (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).

Hooker, S. B.

S. B. Hooker, W. E. Esaias, G. C. Feldman, W. W. Gregg, C. R. McClain, An Overview of SeaWiFS and Ocean Color, Vol. 1 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1992).

King, M. D.

M. Wang, M. D. King, “Correction of Rayleigh scattering effects in cloud optical thickness retrievals,” J. Geophys. Res. 102, 25,915–25,926 (1997).
[CrossRef]

T. Nakajima, M. D. King, “Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. I. Theory,” J. Atmos. Sci. 47, 1878–1893 (1990).
[CrossRef]

McClain, C. R.

S. B. Hooker, W. E. Esaias, G. C. Feldman, W. W. Gregg, C. R. McClain, An Overview of SeaWiFS and Ocean Color, Vol. 1 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1992).

Nakajima, T.

T. Nakajima, M. D. King, “Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. I. Theory,” J. Atmos. Sci. 47, 1878–1893 (1990).
[CrossRef]

Twomey, S.

S. Twomey, T. Cocks, “Remote sensing of cloud parameters from spectral reflectance measurements in the near-infrared,” Beitr. Phys. Atmos. 62, 172–179 (1989).

S. Twomey, T. Cocks, “Spectral reflectance of clouds in the near-infrared: comparison of measurements and calculations,” J. Meteorol. Soc. Jpn. 60, 583–592 (1982).

Wang, M.

Yang, H.

Appl. Opt.

Beitr. Phys. Atmos.

S. Twomey, T. Cocks, “Remote sensing of cloud parameters from spectral reflectance measurements in the near-infrared,” Beitr. Phys. Atmos. 62, 172–179 (1989).

J. Atmos. Sci.

T. Nakajima, M. D. King, “Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. I. Theory,” J. Atmos. Sci. 47, 1878–1893 (1990).
[CrossRef]

J. Geophys. Res.

M. Wang, M. D. King, “Correction of Rayleigh scattering effects in cloud optical thickness retrievals,” J. Geophys. Res. 102, 25,915–25,926 (1997).
[CrossRef]

H. R. Gordon, “Atmospheric correction of ocean color imagery in the Earth Observing System era,” J. Geophys. Res. 102, 17,081–17,106 (1997).
[CrossRef]

J. Meteorol. Soc. Jpn.

S. Twomey, T. Cocks, “Spectral reflectance of clouds in the near-infrared: comparison of measurements and calculations,” J. Meteorol. Soc. Jpn. 60, 583–592 (1982).

Other

S. B. Hooker, W. E. Esaias, G. C. Feldman, W. W. Gregg, C. R. McClain, An Overview of SeaWiFS and Ocean Color, Vol. 1 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1992).

R. S. Fraser, The Effect of Oxygen Absorption on Band-7 Radiance, Vol. 27 of SeaWiFS Tech. Rep. Series, (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).

R. A. Barnes, A. W. Holmes, W. E. Esaias, Stray Light in the SeaWiFS Radiometer, Vol. 31 of SeaWiFS Tech. Rep. Series, NASA Tech. Memo. 104566 (NASA Goddard Space Flight Center, Greenbelt, Md., 1995).

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Figures (9)

Fig. 1
Fig. 1

SeaWiFS O2 A-band absorption correction function P(M) as a function of air mass M for air molecules and aerosols. Redrawn from the results of Ding and Gordon.4

Fig. 2
Fig. 2

SeaWiFS bilinear gain response function for SeaWiFS channels 443, 670, 765, and 865 nm.

Fig. 3
Fig. 3

Water cloud scattering phase function as a function of scattering angle at SeaWiFS wavelengths 412, 670, and 865 nm. The water cloud is assumed to have an effective particle radius of 8 µm.

Fig. 4
Fig. 4

Cloud top reflectance as a function of cloud optical thickness for SeaWiFS wavelengths 670, 765, and 865 nm for a solar zenith angle of 60°, viewing angles of 0° (center) and 45° (edge), and relative azimuthal angle of 90°.

Fig. 5
Fig. 5

SeaWiFS band 8 (865-nm) radiance images acquired in 1997 on (a) 4 September, (b) 26 September, (c) 3 October, and (d) 11 October.

Fig. 6
Fig. 6

PDF (%) of the retrieved cloud optical thickness for 2 ≤ τ c (865) ≤ 6 from the SeaWiFS measurements corresponding to cloudy scenes obtained on the dates shown. There are three retrievals: SeaWiFS band 7 with and without the O2 A-band absorption corrections and from band 8 measurements.

Fig. 7
Fig. 7

PDF (%) of the differences Δτ c ′(765) and Δτ c (765) (%) in retrieved cloud optical thickness for 2 ≤ τ c (865) ≤ 6 from the SeaWiFS measurements corresponding to cloudy scenes measured on the dates listed.

Fig. 8
Fig. 8

Derived values of P A (M) from the four cases of SeaWiFS cloudy scenes compared with values of Ding and Gordon. The error bar corresponding to each point is the variation of ±σ values from the computation, and the solid curve is a least-squares quadratic fit to the points. The curve for the number of data contributed to the average computations in the derivation of P A (M) by the four cases of cloudy scenes is keyed to the right-hand y axis.

Fig. 9
Fig. 9

Differences (%) between the values derived from cloudy scenes and the current SeaWiFS P A (M) and ρ A values for the SeaWiFS band 7 O2 A-band absorption corrections.

Tables (2)

Tables Icon

Table 1 Comparison of Four Cases of Acquired SeaWiFS Cloudy Imagery

Tables Icon

Table 2 Fitting Coefficients for PA(M) = a0 + a1M + a2M2 Derived from Cloudy Scenes Compared with Values from Ding and Gordon

Equations (6)

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

ρtλ=ρrλ+ρaλ+ρraλ+tλρwcλ+tλρwλ,
ρtλ-ρrλ-tλρwcλ=ρaλ+ρraλ.
ρAλ=ρaλ+ρraλ, ρAλ=ρaλ+ρraλ,
ρr,A=1+10Pr,AMρr,A,
ρcλ=ρtλ-ρrλ, ρcλ=ρtλ-ρrλ,
Δτc765=τc765-τc865,  Δτc765=τc765-τc865

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