A Simple Atmospheric Correction Algorithm for MODIS in Shallow Turbid Waters: A Case Study in Taihu Lake

Abstract

A simple atmospheric correction algorithm (SACA) based on a “known” empirical spectral relationship at two bands of MODIS sensor has been developed as a modification to improve the MODIS ocean color products in shallow turbid waters. The analysis results for spectral characteristics suggest that 531, 551, 667, and 678 nm are the optimal bands for constructing the empirical spectral relationship of the SACA algorithm. In order to work efficiently with high adjacency effects and water bottom reflectance in shallow inland lakes, the image statistics method is suggested for the SACA algorithm to determine the aerosol scattering contribution. Using the in situ measurements taken in Taihu Lake on October 27 and 28, 2003, MODIS water-leaving reflectance derived from the atmospheric correction were evaluated using the SWIR and SACA methods, indicating that the SACA algorithm produces a superior performance at visible bands but provides a poor result at NIR bands to the SWIR algorithm. To solve this problem, a combined method is suggested: the SACA algorithm is operated at visible bands, while the SWIR algorithm is executed at NIR bands. Results indicate that the MODIS-derived water-leaving reflectance in shallow turbid water within 20% may be obtained using the combined method. These findings imply that the SACA algorithm is an acceptable atmospheric correction method for deriving the water-leaving reflectance from MODIS data in shallow turbid waters.