Cartographie de l'occupation des terres en zone aride méditerranéenne par télédétection spatiale. Exemple d'application sur les Hauts-Plateaux sud oranais : Méchéria au 1/200000e
Authors: Manière Roger , Chamignon Christel 
Published: April 2020

Today, arid zones are more and more submitted to the influence of man with phenomena of increased desertisation. Its is necessary for these unfavored areas to provide land planning structures integrating all the eco-geographic factors of the environment through a precise knowledge of these areas.

This knowledge is accessible through pluri and interdisciplinary filed works but it is more difficult to get an overall view of these areas through national ecological investigations, due prohibiting costs and execution time. It is necessary to experiment with new techniques in order to fully understand past and present data but also to extend our knowledge to these areas where social pressure is high, with fast and inexpensive new methods.

For this purpose, remote sensing processed data are an adquate tool with its synoptic and diachronic functions. It could efficiently contribute to a complete inventory of human and natural resources and of potential resources, for the study of modifications during long or brief periods of time and to understand existing correlations between biotic and mesologic factors.

Two additional important factors are to be considered when dealing with arid countries :

-first, that the surface area to map and analyze fits perfectly with the possibilities of LANDSAT MSS,

-second, that there excellent climatic conditions with a low interference with clouds permitting for a large choice among actually existing images.

This study was focused on the south algerian which exactly represents typical habitats of steppic countries. The studied zone mesures 480 square kilometers, near the algerio-maroccan border.

The image processing, based on a supervised classification, was the following :

-selection of LANDSAT spectral subset,

-geometric rectification,

-supervised of the tow most significant channels (5 and 7 channels) and combination of among those available, and coding (linear, isopopulation , etc.) in 16 levels,

-combination of the two coded channels into 8 bit image ,

-input of digitized ground truth information in the form of a rasterised map, comparable to image on a pixel by pixel basis,

-computation of histograms for each ground truth category in the new feature space,

-classification of each pixel by comparing its signature to the histograms and applying maximum likelihood method,

-critical analysis of the produced image according to the purpose of the work an by comparison with other data from the same areas,

-definition of new standards, if necessary,

-display maps with production of high resolution films for a definitive edition using VIZIR color.

The map obtained by these image processing presents a land use map on the studied zone. Through this experimentation, numerical processing with supervised classification of MSS LANDSAT data appears a suitable method to produce land use maps in arid zone. The perception level obtained is very satisfactory with regard to the aims of the study. Furthermore, the most important point remains the demonstration of the existing correlation between vegetation and the morpho-pedologic features. Synthetic results obtained through professed remote sensing imagery permit for a clear distinction of any object and also help understand the monitoring ecological factors. The map clearly demonstrates that an overall view of complex systems and correlations between vegetal units and ecological factors are accessibles.

Today, with the Thematic Mapper of LANDSAT and SPOT system, with a higher resolution, will broaden the field of possible applications of satellite data to land use management. Thurthermore the utilisation of satellite imagery for mapping purposes and the inventory of natural resources is completed when a Geographic Information System is established.