IMAGE-ANALYSIS AND CARTOGRAPHY OF SAND HIP MASSIFS ON HIGH-RESOLUTIONIMAGES - APPLICATION TO THE GREAT WESTERN ERG (NW OF ALGERIAN SAHARA)

The northeastern part of the Great Western Erg (Algerian Sahara) is an area with a continuous cover of coarse sands organized in alignments of large domes separated by corridors where deflation prevails. The do mes are covered by small sharp dunes of fine sand (akles). The homogen eity of the substratum does not favour a spectral approach. The cartog raphy of the domes and deflation areas is performed by using the metho ds of Mathematical Morphology. Panchromatic SPOT images are preferred, because the 10m pixel resolution is the only unclassified satellite i mage data that enables differentiation of the landforms. The initial i mage is processed with grey tone filters in order to homogenize the ak le areas. It is next thresholded and the contours of the resulting set s are then regularized. The validation is obtained by comparison with aerial photointerpretation. At a smaller scale, the orientations of th e domes are measured on images from their medial axes.