DETECTION DES CHANGEMENTS D’UN MILIEU NATUREL PAR L’IMAGERIE OPTIQUE LANDSAT DANS LES REGIONS SEMI-ARIDES: CAS DE DJEBEL AOUD ASMA (MONTS DE OULED ALI, SIG, WILAYA DE MASCARA, ALGERIE)

Abstract

Analyzing and understanding the dynamics of physical environments, due to quarrying, is a fundamental issue in detecting change, in semi-arid natural environments. The mountains of Ouled Ali (Beni Chougrane Mountains) contain highly unstable areas that make the region of Sig (Wilaya of Mascara) vulnerable. Observation and qualification of landscape changes is the easiest way for career monitoring. This exploitation has a direct and indirect impact on the ecosystem and the surrounding environment. The slopes of Aoud Asma Mountain (Ouled Ali Mountains) affected by the exploitation of quarries are the subject of our study whose purpose is to characterize their kinematics. To do this, the means are many and varied; each of them has specific properties as regards the type of use, the quantity measured and its scope and accuracy. The change of space mapping by a correlation of optical images is one of these methods.The work methodology adopted is based on the application of Principal Component Analysis (PCA), Intensity, Hue and Saturation of rock (IHS) and Normalized Vegetation Index (NDVI). Two Landsat images were used: Landsat5 image (25thSeptember, 1999) and Landsat7 image (02ndSeptember, 2011). It is followed by a comparison with the ground truth and a mapping of physical space dynamics of the study area. The PCA, IHS and NDVI results allowed us to highlight the bare soils, and the degradation of forest cover and halophyte vegetation. Moreover, the quarrying contributed largely, in some places, to the change of space of AoudAsma Mountain of Ouled Ali Mountains.