Spectrum matching method for estimating the chlorophyll-a concentration, CDOM ratio, and backscatter fraction from remote sensing of ocean color

Abstract

Light emerging from the sea surface carries information about the water constituents, which also includes contributions from inelastic processes, such as Raman scattering, chlorophyll fluorescence, and colored dissolved organic matter (CDOM) fluorescence. The inclusion of inelastic processes, however, has not been fully considered in most of the existing ocean color algorithms. This research presents an approach to substantially decrease the computation time of the nonlinear optimization approach using a look-up table (LUT) to correct for the effects of inelastic scattering. A series of sensitivity tests was conducted to determine the factors required to accurately simulate remote sensing reflectance. Our results show that the inherent optical properties (IOPs) and inelastic scattering play a significant role, whereas the role played by variations of the ambient optical environment and surface wind speed is negligible. An LUT was derived from 22 575 forward simulations using the Hydrolight radiative transfer model. A flexible parameterization of IOPs was formulated by considering all processes of inelastic scattering and a set of three-variable (chlorophyll-a concentration, CDOM ratio, and backscattering fraction) biooptical models. The set of models can be applied to case 1 waters and case 2 waters that happen to be gelbstoff rich, and the volume-scattering phase function can be generated dynamically based on the backscatter fraction. This research may provide a new approach of inversion for including inelastic processes in developing ocean color algorithms.