Total reflectance of wind-roughened sea surfaces: directional properties

Abstract

Abstract Development of global algorithms for remote sensing of oceans in the optical channels requires quantitative estimates on directional properties of sea-surface reflectance to isolate the surface reflected light from the ocean color and the atmospheric haze. Experimental data on directional sea-surface reflectance for different sea states are scarce to nonexistent because no such measurements are made at sea whereas theoretical computations on surface reflectance are rendered difficult because of uncertainties regarding the contribution because of foam. In this paper, we present a unified model to compute directional sea-surface reflectance which is based on the first principles of Fresnel's reflection laws for a semitransparent medium as applied to a nonflat continuously moving boundary such as a wind-roughened sea surface. We have incorporated the contribution resulting from foam by separately computing the reflection from a Lambertian surface for that fraction of sea surface which is covered by foam. Sample results obtained from the model are in agreement with the theoretical estimates established by other authors. The model computes the sea-surface reflectance for any given sea state and for any look angle of a satellite sensor. Source code listing of a FORTRAN computer program for the model proposed in the paper also is presented to allow users to compute the surface reflectance for user-defined inputs.