Atmospheric correction of ocean color sensors: computing atmospheric diffuse transmittance

Using the reciprocal equation derived by Yang and Gordon [Appl. Opt. 36, 7887-7897 (1997)] for atmospheric diffuse transmittance of the ocean-atmosphere system, I examined the accuracy of an analytical equation proposed by Gordon et al. [Appl. Opt. 22, 20-36 (1983)] in computing the atmospheric diffuse transmittance for wavelengths hom 412 to 865 nm for both a pure Rayleigh and a two-layer Rayleigh-aerosol atmosphere overlying a flat Fresnel-reflecting ocean surface. It was found that for viewing angles up to approximately 40 degrees, the analytical formula produces errors usually between 2% and 3% for nonabsorbing and weakly absorbing aerosols and for aerosol optical thicknesses tau(alpha) less than or equal to 0.4. The error increases with an increase in aerosol absorption, aerosol optical thickness, and viewing angle, and with the decrease of wavelength. By a simple numerical fit to modify the analytical formula, the atmospheric diffuse transmittance can be accurately computed usually to within similar to 1% (similar to 0.5% in most cases) for a variety of aerosol models, aerosol optical thicknesses tau(alpha) less than or equal to 0.6, viewing angles a theta less than or equal to 60 degrees, different aerosol vertical structure distribution, and for wavelengths from 412 to 865 nm. (C) 1999 Optical Society of America.