Extraction of vegetation cover in an arid area based on satellite data

Abstract

An attempt is made to derive a vegetation index applicable for extraction of vegetation cover in an extremely arid area such as Taklimakan Desert from Landsat TM image data. In this method a ratio of vegetation coverage in each pixel is computed from the ratio of Landsat TM band 5 and 7 digital values. Then if the value of the ratio is larger than the threshold NDVI (Normalized Vegetation Index, Rouse et. al., 1974) is selected while if the value is less than the threshold SAVI is selected thus the vegetation index consisting of combination of NDVI and SAVI is made which can be defined as NDSAVI. The threshold is decided as follows. The reflectance in the spectral bands corresponding to TM band 5 and 7 is measured for various places in Taklimakan Desert using spectral radiometer which are compared with NDVI and SAVI and an appropriate threshold is decided. It has been confirmed that NDSAVI map shows better correspondence with actual vegetation cover in an arid area than single NDVI or SAVI maps.