Modeling the reflectance spectra of tropical coastal waters

Abstract

This work aims to extract optical parameters of coastal sea water with high sediment and chlorophyll content by fitting reflectance spectra to a model. Sea-truth water sampling campaigns were carried out from Dec 1996 to Dec 1999 in coastal waters around Singapore. In-situ reflectance spectra were acquired using a portable spectroradiometer. Laboratory measurement of the total suspended solid (TSS) and chlorophyll-a (Chl-a) were made from the water samples. The Chl-a concentration ranges from 1 to 90 mg/m3, with an average value of about 10 mg/m3. The three component model for sea water was used to model the reflectance spectra. The model also includes chlorophyll fluorescence and surface reflection due to skylight. Each reflectance spectrum is fitted to the model by finding a set of the fitting parameters that best fits the reflectance curve to the model. The downhill simplex method is employed as the optimization procedure. The chlorophyll absorption coefficient at 440 nm is retrieved and is found to relate to the measured chl-a concentration by a power law relation.