遥感与地理信息系统学报

抽象的

Contribution of Images ETM and GIS for the Detection of Dynamic Changes in Steppic Space in the Wilaya of Naama Under the Combined Effect of Climate Change and Socio-Spatial Mutations

Abdelkrim B*, Mohamed A, Tewfik M, Rachid N

This paper highlights the contribution of landsat images to the dynamic monitoring of the steppe area in the high Oran plains (Algeria). The qualitative and quantitative analysis of the rapid evolution of the landscape and especially the silting up in the cities demonstrate an interesting measurement which allows making a provisional assessment of the current state of the study area. This analysis will raise awareness among the population; the local elected officials and the decision maker about the extent of the sanding phenomenon. By using this analysis, the changes in surface condition between 1957 and 2002 which extracted from different images of Lands at MSS, TM and ETM+had been done. Consequently, three methods of detection of changes (rapid identification and quantification of changes, multidate colored composition technique and dynamic soil cover index techniques) were used to locate the different zones where underwent deep mutations, the special extension of the silting up and the degradation of the grounds inside the regions of the wilaya of Naâmaregion.It is important to note that we used the Olsson model for atmospheric corrections of images. This study is conducted in the high Oran plain which is administratively attached to the wilaya (department) of Naâma. It covers an area of 29,825 km2, between 32°08’and 34°16’ north latitude and 0°09’and 1°43’ west longitude. The use of remote sensing data through the dynamic soil covers index and the diachronic color-composite images allowed focusing the different changes that took place from 1987 to 2002. These changes which concern the changes in the ratio of landscape units in the steppe zone necessitate testing several indices of change (vegetation index, gloss index, curass index and principal component analysis) to minimize errors in the assessment of results of these changes. It is well known that the remote sensing for the result of dynamic changes is influenced by cyclical variations (season, weather conditions). Therefore the radiometric and atmospheric corrections to the images are necessary. Emphasis was placed on the processing of diachronic remote sensing data for the monitoring and development of silting in an arid environment concerning the southwestern part of the high Oran plains. In fact, this analysis revealed that for the entire study region, the surface silted areas increased from 1.38% in 1957 to 42.9% in 2002 or an area of 1,280,762 ha; which corresponds to an extension of 28,461.4 ha per year. It is important to note that the diachronic study involved delicate phases, in particular the choice of the mathematical model for the atmospheric correction (absolute or relative) of the satellite images as well as the determination of the parameter of the real reflectance of the soil for the test samples. This parameter requires adequate equipment (spectroradiometer) or a database on the absolute reflectance of objects. Also, in this study it is recognized that the indices are not very effective for detecting change in an arid zone where the characteristics of the soil and the presence of sand considerably influence the spectral aspect of objects.