Abstract

More than one-third of the land worldwide is located in areas with arid and semiarid climates. Desertification has been increased in these areas during the recent decades. About 80% of that of Iran is located in the arid and semiarid areas. Sand dunes, as an indicator of desert land, cover an area of about 32 million hectares, out of which 12 million hectares have not been stabilized yet. Advancing sand dunes have resulted in much more damage to the agricultural products and urban areas of the region. In this survey, satellite images and aerial photos were employed to evaluate the role of land use changes on desertification within the years 1955, 1997 and 2002. Therefore, IRS (International Revenue Service) images of 2002 and available aerials photos of 1955 and 1997 were used. After making the aerial photos mosaic, processing was dose using ILWIS software. The needed data were completed by field surveying and the land use map was produce for two decades. To produce the land use map using digital processing methods, 10 sample sets (training points) were selected uniformly in the area. After preprocessing including geometric correction, image enhancement and band composition, image classification was done by maximum likelihood method and the land use map was produced. In this phase, the obtained land use map corresponded to the ground truth map, which was achieved using field surveying and recording of the coordinates of the points with GPS pixel to pixel, and accuracy obtained from the numerical classification was estimated to be 0.3%. Then, due to the obtained low accuracy, the visual interpretation method was used to produce the land use map, so the accuracy of 78.5% was achieved. Finally, the area of each land use and the rate of changes were calculated. The results indicated a decrease of 2000 ha in the desert area from 1955 to 1997 and of 160 ha from 1997 to 2002 as well as an increase in the area of the other land uses. The results showed no desertification in the study area, even though land degradation could obviously be identify in the area, resulting from the changes of gardens and agricultural land uses to industrial and urban areas.

Key words: Desertification, land use, remote sensing, IRS images, Ardakan, Iran.