Ability of Landsat satellite images 5, 7 in determining Alkalinity of soil changes in Qhahavand plain (Hamedan province)

Remote sensing technology is useful tool for spatial and temporal monitoring of natural phenomenon. Secondary salinization is known as the main causes of soil degradation where inappropriately land management occurred in a region. Total saline and sodic soils in Hamedan province are estimated at 70,000 hectare that includes 9.5 percent of total cultivable lands in this province. This paper tries to show important aspects of applying remote sensing in classification of sodic soils in Qahavand plain. The objective of this study is to monitor the sodic soils by using satellite information landsat-5&7. Classification of satellite imagery for alkalinity was carried out by investigation various bands and indexes such as PCA57, PCA123, NDVI, GRI, BRI. The supervised classification and spectral response angular mapping method used to classify the images. The soil maps were prepared by geographic information system in 1:50,000 scale. The results showed that total sodic soils areas were extended during last 11 years by 9.8 percent. The change in low sodisity class (A1) was 23.1 percent; in medium sodisity class (A2) was 13.7 percent and in sever sodisity class (A3) was 0.3 percent. The area of bare soils was 3005 hectares which is estimated 8446 hectares now and increased by 181 percent. The most important reasons for extension of sodic soils in this region are lack of proper land use and water management and conversion of land uses.