Modification of SeaDAS SWIR atmospheric correction scheme for accurate retrieval of NIR remote sensing reflectance in the river delta regions of the world

Abstract

Coastal waters in the vicinity of the river delta regions of the world are characterized by significant concentrations of suspended sediments. To estimate the water sediment load from satellite observations, an important step is to accurately remove the optical effects of the intervening atmosphere. The NASA SeaDAS code [1] has been shown to accurately correct MODIS satellite data for atmospheric effects over most aquatic regimes, using near infrared (NIR) bands where water turbidity is low, and shortwave infrared (SWIR) bands where the NIR bands indicate high turbidity [2]. However, at very high sediment loads, of circa 500 g/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and above - and this is not an unusually high level in delta regions - the SWIR bands can themselves be influenced by the suspended sediment and their utility for atmospheric correction thus compromised. Indeed, the ocean color NIR bands saturate under these conditions and so become unviable for any manner of atmospheric correction. We have employed the MODIS water vapor bands in the 900 nm region of the spectrum to provide a correction to the 1.24 µm band MODIS reflectance, thereby extending the utility of the SeaDAS SWIR atmospheric correction to very high sediment concentration waters.