CHANGE DETECTION OF IRRIGATED CROP LAND USING SATELLITE IMAGERY

摘要

Natural resources management and environment follow up (mapping of cropland, delimitation of areas which are sensitive to desertification, fight of poverty, etc.) need appropriate decisions to be made. Or, those decisions can not be made without knowledge of the spatial extent and its environment. In the work frame of the Conservation of Biodiversity by Transhumance in the High Atlas project (CBTHA) which is taking place in Ouarzazate South of Morocco and covers about 1.6 millions of hectares, a study on the evaluation of agriculture settlements and deforestation is to be undertaken. To satisfy the purpose of this study, mapping tasks should be realized as a first step for gathering the best knowledge of actual irrigated crop land extent as well as the general evolution tendency. Nowadays, remote sensing and GIS are known as powerful tools for mapping, analysis and decision making. Hence, using these fields, the present study focuses on mapping the change in irrigated crop land from 1970 to 2006. To achieve this goal, three dates were selected: 1970, 1996 and 2006. Spot XS satellite images of 20 m resolution for 1996 and 2006 dates were acquired. Image processing which was undertaken include, image enhancement using histogram match, rectification, image mosaic as well as extraction of the area of interest. Pixel classification using maximum of likelihood algorithm followed by fuzzy classification was realized using the two sets of images acquired on 1996 and 2006. Moreover, for the 1970 data, irrigated crop land was digitized directly from georeferenced topographic maps at scale of 1/100000. Results from change detection show that there exists a high increase in irrigated crop land extent from 1970 to 2006. Furthermore, statistical as well cartographic results for the three dates will be used as a base to help in decision making during the evaluation of agriculture settlements and deforestation.