The Use of Ers Data for Monitoring of Land Cover Change in Sahelian Regions the Example of the Delta of the Niger River (mali)

Vegetation analysis in semi arid regions is in high demand and remote sensing applications are well established. In the field of change detection of Sahelian landscapes, one has to inventory states of vegetation at different recording dates. The Inland Niger Delta (Mali) is an azonal hydrographical landscape complex within the semi arid West African zone of the Sahel with water available through all the year. The changes in the land cover is due to pre-flood and post flood hydrological conditions of the Niger, which depends to seasonal and annual pluviometric events. Our purpose is to study different ERS images on the same area, in order to survey changes in the landscape between different seasons and different years. One of the advantages of using ERS data upon Landsat and Spot images for studying the inter seasonal and interannual changes over this large wetland, is that the view of the ground is no more obstructed by the frequent clouds and mist as it is usually on passive remote sensing images. In order to observe with accuracy annual changes as well as seasonal one, we have selected a set of ERS images in the region of Mopti, taken in the pre-flood and post flood periods between 1992 and 1996. We first have reduced the speckle on ERS images by means of appropriate filters in order get a more accurate vision of change. This changes are detected with colour making images by RGB techniques from three dates images. On the resulting images, major variations in the back scattering of landscape units will appear as coloured flat zones. With the help of ground truth and aerial photographs of some wellknown areas, the coloured zones are interpreted whether as flood, or as changes in the vegetation cover.