Potential of ASAR/Envisat Data for Mud Bank Monitoring in French Guiana Compared to ASTER Imagery

Abstract

In French Guiana, the constant migration of large mud banks resulting from the Amazon River's sedimentary discharge has a negative impact on the local economy. Two radar images from the new ASAR/Envisat sensor have been analysed and compared to one ASTER image to assess their potential for mud bank monitoring. Bathymetric data were also recorded at times close to those of the satellite acquisitions, enabling a comparative study of the mud bank morphology and bathymetry and satellite information.The emerged parts of the mud banks, whether consolidated/solid (slikke or mudflats, mud bars, etc.) or fluid mud are easily detectable on the ASAR images. However, the results show that mud bank covered by a shallow layer of water (a few tens of centimetres) is not detectable on ASAR images. For deeper waters the ASAR signal is independent of water depth. ASAR's multipolarized images provide little more information than that obtained from older sensors having only a single polarization (ERS-1/2 and RADARSAT-1). The Horizontal transmit and Horizontal receive (HH) and Vertical transmit and Vertical receive (VV) polarizations have equivalent cartographic potentials, markedly superior to that provided by the VH polarization. However, the VH brings out certain information that is hard or impossible to see in HH or VV, for example, some offshore emerged portions of the banks, and provides a better separation between water and coastal mangrove forest. The ASTER image enables effective mapping of the extent of emerged mud banks and identification of three classes of water depth.