DEVELOPMENT AND IMPLEMENTATION OF SPECTRAL CRUST INDEX OVER DUNE SANDS

Advantage is taken of a unique spectral feature of soil biogenic crust containing cyanobacteria. It has been shown that the special phycobil in pigment in cyanobacteria contributes in producing a relatively high er reflectance in the blue spectral region than the same type of subst rate without the biogenic crust. A spectral crust index (CI) has been developed, based on the normalized difference between the RED and the BLUE spectral values: CI = 1 - (RED - BLUE)/(RED + BLUE). Applying the index to a sand dune environment, it has been shown that the CI can b e used to detect and to map, from remote sensing imagery, different li thological morphological units, such as, active sands, crusted interdu ne areas and playas, which are expressed in the topography. As a mappi ng tool the CI image is much more sensitive to the ground features tha n the original images. The absence, existence, and distribution of soi l crust are an important information for desertification and climate c hange studies. They are also highly valuable information for developin g agricultural regions and/or infrastructures in arid environments sin ce soil crusts contribute to soil stability, soil build-up, soil ferti lity, and to the soil water regime. The application of the proposed CI can be performed with imagery acquired by any sensor which contains t he blue band. Currently, the most common data sources are colour aeria l photographs and Landsat TM images as demonstrated in this paper. How ever, CI should be applicable to other sensors such as the SPOT-VEGETA TION, MOMS-2P, SeaWiFS and MODIS which will be available in the coming years.