Abstract

In attempting to observe the color of the ocean from satellites, it is necessary to remove the effects of atmospheric and sea surface scattering from the upward radiance at high altitude in order to observe only those photons which were backscattered out of the ocean and hence contain information about subsurface conditions. The observations that (1) the upward radiance from the unwanted photons can be divided into those resulting from Rayleigh scattering alone and those resulting from aerosol scattering alone, (2) the aerosol scattering phase function should be nearly independent of wavelength, and (3) the Rayleigh component can be computed without a knowledge of the sea surface roughness are combined to yield an algorithm for removing a large portion of this unwanted radiance from satellite imagery of the ocean. It is assumed that the ocean is totally absorbing in a band of wavelengths around 750 nm and shown that application of the proposed algorithm to correct the radiance at a wavelength λ requires only the ratio () of the aerosol optical thickness at λ to that at about 750 nm. The accuracy to which the correction can be made as a function of the accuracy to which can be found is discussed in detail. A possible method of finding from satellite measurements alone is suggested.

© 1978 Optical Society of America

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References

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  1. V. Klemas, M. Otley, C. Wethe, “Monitoring Coastal Water Properties and Current Circulation with ERTS-1,” Third ERTS-1 Symposium, Washington D.C., (10–14 December 1973).
  2. G. A. Maul, H. R. Gordon, Remote Sensing Environ. 4, 95 (1975).
    [CrossRef]
  3. G. L. Clark, G. C. Ewing, C. J. Lorenzen, Science 167, 1119 (1970).
    [CrossRef]
  4. S. Q. Duntley et al., “Ocean Color Analysis,” SIO Ref. 74-10, Visibility Lab., San Diego, Calif. (April1974).
  5. W. A. Hovis, K. C. Leung, Opt. Eng. 16, 157 (1977).
    [CrossRef]
  6. H. R. Gordon, Appl. Opt. 15, 1974 (1976).
    [CrossRef] [PubMed]
  7. In Ref. 6 it is shown that placing a hypothetical Lambertian reflector of albedo A just beneath the sea surface results in nearly the same computed upward radiance at the top of the atmosphere as that obtained in complete simulations of radiative transfer in the ocean-atmosphere system as long as A = R. r in Eq. (1) is the ratio of the number of photons which interact twice with this Lambertian surface to the number which interact once.
  8. After I1(0,ϕ) is removed from I(0,ϕ), one is still faced with the fact that the photons leaving the ocean have to pass through the atmosphere, reducing the contrast with which horizontal variations in R (and hence ocean properties) can be observed. This imaging aspect of the problem will be dealt with in a later paper.
  9. G. N. Plass, G. W. Kattawar, F. E. Catchings, Appl. Opt. 12, 314 (1973).
    [CrossRef] [PubMed]
  10. W. J. Wiscombe, J. Quant. Spectrosc. Radiat. Transfer 16, 637 (1976).
    [CrossRef]
  11. G. W. Kattawar, J. Quant. Spectrosc. Radiat. Transfer 15, 839 (1975).
    [CrossRef]
  12. D. Deirmendjian, Electromagnetic Scattering on Spherical Polydispersions (Elsevier, New York, 1969).
  13. K. Bullrich, Scattered Radiation in the Atmosphere and the Natural Aerosol, in Advances in Geophysics (Academic P., New York, 1964), Vol. 10.
  14. G. N. Plass, G. W. Kattawar, S. J. Hitzfelder, Appl. Opt. 15, 632 (1976).
    [CrossRef] [PubMed]
  15. C. Cox, W. Munk, J. Opt. Soc. Am. 44, 838 (1954).
    [CrossRef]

1977

W. A. Hovis, K. C. Leung, Opt. Eng. 16, 157 (1977).
[CrossRef]

1976

1975

G. W. Kattawar, J. Quant. Spectrosc. Radiat. Transfer 15, 839 (1975).
[CrossRef]

G. A. Maul, H. R. Gordon, Remote Sensing Environ. 4, 95 (1975).
[CrossRef]

1973

1970

G. L. Clark, G. C. Ewing, C. J. Lorenzen, Science 167, 1119 (1970).
[CrossRef]

1954

Bullrich, K.

K. Bullrich, Scattered Radiation in the Atmosphere and the Natural Aerosol, in Advances in Geophysics (Academic P., New York, 1964), Vol. 10.

Catchings, F. E.

Clark, G. L.

G. L. Clark, G. C. Ewing, C. J. Lorenzen, Science 167, 1119 (1970).
[CrossRef]

Cox, C.

Deirmendjian, D.

D. Deirmendjian, Electromagnetic Scattering on Spherical Polydispersions (Elsevier, New York, 1969).

Duntley, S. Q.

S. Q. Duntley et al., “Ocean Color Analysis,” SIO Ref. 74-10, Visibility Lab., San Diego, Calif. (April1974).

Ewing, G. C.

G. L. Clark, G. C. Ewing, C. J. Lorenzen, Science 167, 1119 (1970).
[CrossRef]

Gordon, H. R.

H. R. Gordon, Appl. Opt. 15, 1974 (1976).
[CrossRef] [PubMed]

G. A. Maul, H. R. Gordon, Remote Sensing Environ. 4, 95 (1975).
[CrossRef]

Hitzfelder, S. J.

Hovis, W. A.

W. A. Hovis, K. C. Leung, Opt. Eng. 16, 157 (1977).
[CrossRef]

Kattawar, G. W.

Klemas, V.

V. Klemas, M. Otley, C. Wethe, “Monitoring Coastal Water Properties and Current Circulation with ERTS-1,” Third ERTS-1 Symposium, Washington D.C., (10–14 December 1973).

Leung, K. C.

W. A. Hovis, K. C. Leung, Opt. Eng. 16, 157 (1977).
[CrossRef]

Lorenzen, C. J.

G. L. Clark, G. C. Ewing, C. J. Lorenzen, Science 167, 1119 (1970).
[CrossRef]

Maul, G. A.

G. A. Maul, H. R. Gordon, Remote Sensing Environ. 4, 95 (1975).
[CrossRef]

Munk, W.

Otley, M.

V. Klemas, M. Otley, C. Wethe, “Monitoring Coastal Water Properties and Current Circulation with ERTS-1,” Third ERTS-1 Symposium, Washington D.C., (10–14 December 1973).

Plass, G. N.

Wethe, C.

V. Klemas, M. Otley, C. Wethe, “Monitoring Coastal Water Properties and Current Circulation with ERTS-1,” Third ERTS-1 Symposium, Washington D.C., (10–14 December 1973).

Wiscombe, W. J.

W. J. Wiscombe, J. Quant. Spectrosc. Radiat. Transfer 16, 637 (1976).
[CrossRef]

Appl. Opt.

J. Opt. Soc. Am.

J. Quant. Spectrosc. Radiat. Transfer

W. J. Wiscombe, J. Quant. Spectrosc. Radiat. Transfer 16, 637 (1976).
[CrossRef]

G. W. Kattawar, J. Quant. Spectrosc. Radiat. Transfer 15, 839 (1975).
[CrossRef]

Opt. Eng.

W. A. Hovis, K. C. Leung, Opt. Eng. 16, 157 (1977).
[CrossRef]

Remote Sensing Environ.

G. A. Maul, H. R. Gordon, Remote Sensing Environ. 4, 95 (1975).
[CrossRef]

Science

G. L. Clark, G. C. Ewing, C. J. Lorenzen, Science 167, 1119 (1970).
[CrossRef]

Other

S. Q. Duntley et al., “Ocean Color Analysis,” SIO Ref. 74-10, Visibility Lab., San Diego, Calif. (April1974).

V. Klemas, M. Otley, C. Wethe, “Monitoring Coastal Water Properties and Current Circulation with ERTS-1,” Third ERTS-1 Symposium, Washington D.C., (10–14 December 1973).

D. Deirmendjian, Electromagnetic Scattering on Spherical Polydispersions (Elsevier, New York, 1969).

K. Bullrich, Scattered Radiation in the Atmosphere and the Natural Aerosol, in Advances in Geophysics (Academic P., New York, 1964), Vol. 10.

In Ref. 6 it is shown that placing a hypothetical Lambertian reflector of albedo A just beneath the sea surface results in nearly the same computed upward radiance at the top of the atmosphere as that obtained in complete simulations of radiative transfer in the ocean-atmosphere system as long as A = R. r in Eq. (1) is the ratio of the number of photons which interact twice with this Lambertian surface to the number which interact once.

After I1(0,ϕ) is removed from I(0,ϕ), one is still faced with the fact that the photons leaving the ocean have to pass through the atmosphere, reducing the contrast with which horizontal variations in R (and hence ocean properties) can be observed. This imaging aspect of the problem will be dealt with in a later paper.

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Figures (2)

Fig. 1
Fig. 1

The three aerosol scattering phase functions used in the radiative transfer computations.

Fig. 2
Fig. 2

Normalized radiance in the single scattering approximation computed for the phase functions resulting from Eq. (4) for various values of ν.

Tables (6)

Tables Icon

Table I P450(θ)/P750(θ) as a Function of ν

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Table II Percent Error in Using Eq. (6)

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Table III Computed Values of R′ Using the True Value of . Actual Value of R′ is 0.085

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Table IV Computed Values of −(ΔR′Δ)

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Table V Accuracy in ν Required for Δ = ±0.17 at 443 nm

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Table VI Percentage Error in Eq. (6) for the OTHG (0.6) with θ0 = 0 and a 10-Knot Wind

Equations (10)

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I ( θ , ϕ ) = I 1 ( θ , ϕ ) + I 2 ( θ , ϕ ) R 1 r R ,
I 1 λ = I IA λ + I 1 R λ ,
I 1 λ ( θ ) = I 1 A λ ( θ ) + I 1 R λ ( θ ) ,
d n d r = c r ( ν + 1 ) ,
τ A ~ λ ( ν 2 ) ,
I 1 λ = I 1 R λ + λ ( I 750 I 1 R 750 ) ,
R = [ R / ( 1 r R ) ]
I 443 ( θ , ϕ ) = I 1 443 ( θ , ϕ ) + I 2 443 ( θ , ϕ ) R
R = R true + ( Δ R / Δ ) ( true ) .
τ A 443

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