干旱区生态环境知识资源中心

The Biological Soil Crusts(BSC) (also known as organic or microphytic crust) can be formed by different combinations of microphytic communities including mosses, lichens, liverworts, algae, fungi, cyanobacteria (=blue-green algae or Cyanophyta), as wellas bacteria. Large areas of sand fields in arid and semi-arid regions are covered by BSC. Remote sensing distinction should be made between physical and biogenical crust formations. It was reviewed the advances of domestic and overseas studies of BSC spectral characteristics, as well as spectral reflectance measurement in situ of our workgruop. When the BSC is wet, it turns green, a notable change in the reflectance curve occurs. The wet BSC’s spectral reflectance curve is similar to those of the higher plants and therefore may lead to misinterpretation of the vegetation dynamics and to overestimation of ecosystem productivity. This spectral feature produces a much higher NDVI value for the wet moss BSC than for the dry moss BSC(0.65 vs. 0.30 units, respectively), a higher NDVI value for the wet algae BSC than for the dry algae BSC(0.30 vs. 0.15 units, respectively). The "maximum value composite" (MVC) technique is used to eliminate the effect of clouds and haze from vegetation maps. Misinterpretation of the vegetation dynamics could be more severe due to the MVC technique used to compose the global vegetation maps in the study of vegetation dynamics. But relatively limited research has been conducted to investigate the spectral characteristics of BSC change with different moisture conditions and under different seasons. More research works could be considered in spectral characteristics of BSC. The researches would be useful for detecing and mapping BSC, from remote sensing imagery. It also is to the advantage to employ Vegetation Index wisely.