Abstract

A quasisingle scattering (QSS) model is developed for the radiative transfer of light generated at 683 nm through the solar-induced fluorescence of chlorophyll a contained in marine phytoplankton. The model utilizes the product of the spectral scalar irradiance (as a function of depth) at the exciting wavelength and the phytoplankton spectral absorption coefficient for the fluorescence source function. The radiative transfer equation is then solved using the QSS approximation. The results of the computational model are compared to, and validated by, a dual wavelength (excitation–emission) Monte Carlo simulation of the entire process including all orders of multiple scattering at both wavelengths. The QSS solution for the fluoresced irradiance, which utilizes the Monte Carlo results for the exciting wavelength, agrees with the results of the full Monte Carlo simulation to within ~2%. In contrast, while the simpler solution used by Gordon¹ works well very near the surface, it fails to predict the correct fluorescence as a function of depth. The QSS model is combined with a biooptical model of the spectral inherent optical properties of phytoplankton to study the influence of the chlorophyll concentration and its vertical profile on the apparent optical properties of the ocean within the fluorescence band. The practice of modeling the fluorescence with the aid of a spectrally averaged plankton absorption is examined and shown to be valid only near the surface.

© 1991 Optical Society of America