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 radiance (L-w) to the top of the atmosphere: the angular distribution of upwelling radiance beneath the sea surface (L-w) and the concentration and optical properties of aerosols in the atmosphere. We examine these factors and (1) show that the error in L-w that is induced by assuming L-u is uniform (i.e., in treating the subsurface reflectance by the water body as Lambertian) is significant in comparison with the other errors expected in K-w only at low phytoplankton concentration and then only in the blue region of the spectrum; (2) show that when radiance ratios are used in biophysical algorithms the effect of the uniform-L-u approximation is even smaller; and (3) provide an avenue for introducing accurate computation of the uniform-L-2 diffuse transmittance into atmospheric correction algorithms. In an Appendix the reciprocity principle is derived for a medium in which the refractive index is a continuous function of position. (C) 1997 Optical Society of America.