Bidirectional reflectance of oceanic waters: A comparison of modeled and measured upward radiance fields

Abstract

The bidirectional reflectance of oceanic waters is conveniently described in a normalized way by forming the ratio of the up welling irradiance Eu to any up welling radiance Lu(θ′, φ). This ratio, Q[θ′, θ0, (φ0 − φ)], where θ′, φ are the nadir and azimuth angles for the upward radiance and θ0, φ0 are the zenith and azimuth angles of the Sun, has been determined from measurements at sea and computed via Monte Carlo simulations using the inherent optical properties measured in the field and appropriate boundary conditions (clear sky, no wind, varying Sun angle). Experimental and computed Q values are in excellent agreement. This successful comparison confirms the importance of the bidirectional character of ocean reflectance, already pointed out from a purely numerical approach without field validation, and corroborates the extended range of the Q variations. The later point is of importance when interpreting the marine signals detected by an ocean color satellite‐borne sensor. The validation is extended by considering the historical data for the radiance distributions in Lake Pend Oreille determined at various depths. The closure issue in ocean optics is examined by solving the direct problem of radiative transfer and through a model‐data comparison in terms of radiance field.