Concentrations of chlorophyll, suspended matter, and gelbstoff in case II waters derived from satellite coastal zone color scanner data with inverse modeling methods

Abstract

Color ratio techniques used to derive chlorophyll concentrations from radiance data of the coastal zone color scanner (CZCS) fail in areas with high concentrations of suspended matter and gelbstoff (optically defined as case II water). In order to take into account all water constituents which modify the backscattered radiation field as well as the aerosol path radiance, an inverse modeling technique based on a two‐flow radiative transfer approximation and a simplex optimization procedure has been developed. It uses simultaneously the radiances of the first four CZCS spectral channels and minimizes the χ2 difference between the modeled and CZCS‐derived “Rayleigh‐corrected radiances.” The two‐flow model is calibrated with a set of radiance data which was simulated with a matrix‐operator radiative transfer model. In a first test, the inverse modeling procedure has been used to produce maps of the quantitative distributions of phytoplankton chlorophyll, suspended matter (dry weight), and gelbstoff; aerosol path radiance; and signal depth of the North Sea. By including the aerosol path radiance as a variable, the procedure implies the atmospheric correction. A map of the residual χ2 values indicates the success of the retrieval for each of the pixels.