Mangrove mapping in North-Western Madagascar using SPOT-XS and SIR-C radar data

Abstract

Within the framework of an environmental impact study of aquaculture activities in the coastal marsh of Mahajamba (North-Western Madagascar), an assessment of the environmental conditions existing prior to the onset of aquaculture activities (production began in October, 1993) is essential. To this end, the area was mapped using SPOT-XS data, which made it possible to define the main ecodynamic tendencies of the mangroves before the development of the rearing ponds. The aim was then to implement fast, precise and reliable mapping methods, making it possible to follow mangrove alterations resulting from these aquaculture activities. Analysis of the radiometric behaviour of the various plant formations of the marsh, based on SIR-C radar data, revealed that the discrimination between these formations is easier when the frequency used is low and the polarization is crossed. Thematic analysis using textural classification was carried out with the L-band and polarization VH. The results generated are promising insofar as the mapping of mangroves is concerned with a fast treatment time and acceptable precision of the results.