Abstract

The NOARL optical model, a Monte Carlo simulation of the radiative transfer equation, has been updated with a newer and more accurate algorithm for estimating the shape factor, a relatively neglected aspect of the two-flow approximation of the radiative transfer equation. In addition, the model has been ported to the Cray Y-MP of the North Carolina Super Computing Center. Two series of simulations have been carried out so far: a simulation of light penetration at 440 nm in clear ocean waters with increasing concentrations of chlorophyll, and a simulation of light penetration in clear ocean water with no organic matter over the wavelength region 430- 660 nm. The new shape factor algorithm has an accuracy >0.1%. In the clear ocean system with algae the shape factors for the downwelling and upwelling radiative fluxes differ from each other increasingly with increase in algae concentration. The ratio of these factors r_u/r_d approaches 3.0 at the highest algae concentrations simulated so far, the maximum concentrations of algae/chlorophyll for open ocean waters. The shape factors for both downwelling and upwelling radiant flux streams increase by 10-20% with increase of depth in the upper ocean layers. Without taking internal radiant emission into account (Raman scattering, fluorescence), the shape factors for clear ocean water without organic matter also deviate increasing from each other with increase in wavelength. The greater the deviations of the shape factors from each other and from the value of 1.0 the less reliable the two-flow approximation becomes.

© 1991 Optical Society of America