Olivier Guelorget

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

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.

Remote sensing as a tool for diagnosis of water quality in indonesian seas

Shrimp development in Indonesia, after a decade of strong expansion and intensification, began to be faced with critical problems of mortality. General degradation of coastal waters is likely to be the major reason, and this mainly occurs on sites in the Java Sea which appear as confined seas subjected to high telluric effluent levels and anthropic pressure. Remote sensing provides synoptic vision over large areas. Several scenes were processed for land-use mapping using conventional classification techniques. In this study, this was specifically done to determine water quality. A general empirical relation for the Java Sea, independent of time and place, was found between image and field data, namely pigments and suspended matter. Applying this relation to a new site provides an initial approach to water type and, together with land use mapping, a preliminary assessment of the suitability of the area for shrimp aquaculture development. It also provides guidance for efficient subsequent field sampling. Recommendations are given for use of remote sensing to improve site assessment and monitoring.