IMAGE-ANALYSIS AND CARTOGRAPHY OF SAND HIP MASSIFS ON HIGH-RESOLUTION IMAGES - 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 domes are covered by small sharp dunes of fine sand (akles). The homogeneity of the substratum does not favour a spectral approach. The cartography of the domes and deflation areas is performed by using the methods of Mathematical Morphology. Panchromatic SPOT images are preferred, because the 10m pixel resolution is the only unclassified satellite image data that enables differentiation of the landforms. The initial image is processed with grey tone filters in order to homogenize the akle areas. It is next thresholded and the contours of the resulting sets are then regularized. The validation is obtained by comparison with aerial photointerpretation. At a smaller scale, the orientations of the domes are measured on images from their medial axes.