REMOTE-SENSING OF OCEAN COLOR - ASSESSMENT OF WATER-LEAVING RADIANCE BIDIRECTIONAL EFFECTS ON ATMOSPHERIC DIFFUSE TRANSMITTANCE

Two factors influence the diffuse transmittance (t) of water-leaving r adiance (L-w) to the top of the atmosphere: the angular distribution o f upwelling radiance beneath the sea surface (L-w) and the concentrati on and optical properties of aerosols in the atmosphere. We examine th ese factors and (1) show that the error in L-w that is induced by assu ming L-u is uniform (i.e., in treating the subsurface reflectance by t he water body as Lambertian) is significant in comparison with the oth er errors expected in K-w only at low phytoplankton concentration and then only in the blue region of the spectrum; (2) show that when radia nce ratios are used in biophysical algorithms the effect of the unifor m-L-u approximation is even smaller; and (3) provide an avenue for int roducing accurate computation of the uniform-L-2 diffuse transmittance into atmospheric correction algorithms. In an Appendix the reciprocit y principle is derived for a medium in which the refractive index is a continuous function of position. (C) 1997 Optical Society of America.