Coastline and mudbank monitoring in French Guiana: contributions of radar and optical satellite imagery

The constant migration of mudbanks resulting from the sedimentary discharge of the Amazon River has an enormous impact on the French Guianese economy. Consequently, there is great local interest in finding tools that can be used in mapping and monitoring the mudbank migration with an acceptable level of reliability and a high frequency of measurement. This involves the ability to detect submarine mudbanks that interfere with access to port channels and impede navigation. Radar and optical satellite images of French Guiana acquired between 1997 and 2001 have been analysed to assess their utility in detecting mudbanks and monitoring coastline change. In the present study, the information derived from radar and optical satellite imagery was analysed with respect to tidal height. The influence of the radar incidence angle was considered, as well as the advantages of having multidate sequences when mapping coastal zones undergoing significant change. A comparative study between radar (European Remote Sensing Satellite (ERS) and RADARSAT) and optical (advanced spaceborne thermal emission and reflection radiometer (ASTER)) images was also conducted. The results show that low-angle radar is more suitable for detecting mudbanks, whereas high-angle radar is more appropriate for monitoring coastline change. Emerged mudbanks and mudbanks under a shallow layer of water (a few tens of centimetres at the most) are easily detectable in radar images. For high tidal levels, the optical images provide more information on the mudbanks than the radar images. Conversely, for low tidal levels, the information on the mudbanks is more detailed with radar imagery.