[Spectral characteristics of biological soil crusts in Gurbantonggut Desert, Xinjiang].

Large areas of desert in arid and semi-arid regions are covered by biological soil crusts. Tracking the presence, distribution and disappearance of biological soil crusts is important for ecosystem management of desert regions and provides highly valuable information about desertification and climate change studies in arid and semiarid environments. The objective of the present paper is to analyze the unique reflectance spectral features of three types of biological soil crusts (moss, lichen and algae) relative to bare sand and dry plant. The measurements for the reflectance of bare sand, dry plant and biological soil crusts derived from the field survey were performed in the laboratory under dry condition. The reflectance of biological soil crusts after they were hydrated with 0.5 and 1.0 mm water respectively was also measured in the laboratory. It was found that the reflectance of crusts was much lower than that of bare sand throughout the Vis-SWIR region. Moreover, the reflectance of crusts exhibited a slightly flattening plateau between 600 and 750 nm, attributed to the absorption of photosynthetic pigments. Based on the spectral features of biological soil crusts, it was proposed that continuum removal technique could be used to retrieve the coverage of biological soil crusts. A significant correlation between the minus logarithm of the absorption depth of the continuum removal spectra and the coverage of biological soil crusts was found (r2 = 0.990 7). The liquid-water hydration experiment demonstrated that the absorption of photosynthetic pigments was strengthened after hydration, making the detection of biological soil crusts much easier.