Retrieval of total suspended matter concentration in the Yellow and East China Seas from MODIS imagery

Abstract

A retrieval algorithm, of total suspended matter (TSM) concentration in the Yellow Sea (YS) and East China Sea (ECS) was developed using observations made in the 2003 Spring and Autumn cruises over the YS and the ECS. Analysis of the in-situ backscattering coefficients of the suspended particles ( b bp) indicates that the accuracy becomes worse when the concentration of TSM ( C TSM) is higher than 20 mg/l. The accuracy of the b bp is improved by using a bio-optical model in which b bp is optimized with a non-linear least-square Levenberg–Marquardt method. The remote sensing reflectance ( R rs) is obtained by means of the optimization. The optimized R rs for waters with C TSM higher than 20 mg/l, together with the measured R rs for waters with C TSM lower than 20 mg/l, are used to establish the relationships between R rs(748), R rs(869) and R rs(645), which are used in the iterative method for atmospheric correction. Two atmospheric correction algorithms are switched according to the water turbidity. The shortwave infrared wavelengths (SWIR) method is used for waters with high-turbidity, and the iterative method is used otherwise. Results of the atmospheric correction were then applied to the Tassan model modified in this paper to compute the C TSM. Comparison between the retrieval results from MODIS imagery and the in-situ measurements indicates that the algorithms described in this paper can provide a reliable estimation of the C TSM distributions in the YS and ECS.