ABSORPTION AND SCATTERING ESTIMATES FROM IRRADIANCE MEASUREMENTS - MONTE-CARLO SIMULATIONS

A method of estimating the absorption (a), scattering (b), and backscattering (b(b)) coefficients of a homogeneous ocean based on near-surface measurements of the beam attenuation coefficient (c), the irradiance reflectance (R), and the attenuation coefficient of downwelling irradiance (K(d)) is proposed, and it is tested with Monte Carlo simulations of radiative transfer in the ocean-atmosphere system. The technique utilizes the variation of R with solar zenith angle to estimate the value R would have if the sun were at zenith and the atmosphere were removed. This value of R is then combined with K(d) to derive b(b) and the ratio of scattering to beam attenuation, from which a and b are obtained. In addition, the volume scattering function beta(alpha) for scattering angles 60-degrees less-than-or-similar-to alpha less-than-or-similar-to 150-degrees is also estimated. Such estimates of b(b) and beta(alpha), which are based on the diffuse light field existing over volumes of the order of 10-1,000 m3, are important in assessing the applicability of measurements made with classical scattering instruments (sampling volume approximately 1 cm3) to predicting radiative transfer in the upper layers of the ocean. Direct application of the method is limited to situations in which the mixed layer is sufficiently deep and in which inelastic processes, e.g. Raman scattering and fluorescence, make negligible contributions to K(d) and R near the sea surface.