It is shown that relative higher reflectivity of the crust in the blue region is caused due to the spectral characteristics of the phycobilins. This work is a first step towards mapping biogenic crusts by using airborne or spaceborne sensors which have the capability to detect in the blue band. Surprisingly, in semi-arid regions, relatively high values of NDVI were measured in landscapes where little, if any photosynthetic activity of higher plants exists. We found that the spectral reflectance curves of lower plants can be similar to those of the higher ones and their derived NDVI values can be as high as 0.30 units. We conclude that in semi-arid environments, the reflectance of lower plant communities may lead to misinterpretation of the vegetation dynamics and overestimation of ecosystem productivity.
Advantage is taken of a unique spectral feature of soil biogenic crust containing cyanobacteria.
Chapter 4 shows that the special phycobilin pigment in cyanobacteria contributes in producing a relatively higher reflectance in the blue spectral region than the same type of substrate without the biogenic crust. As a mapping tool the CI image is much more sensitive to the ground features than the original image. The absence, existence, and distribution of soil crust are an important source of information for desertification and climate change studies. The application of the proposed CI can be performed with imagery acquired by any sensor which contains the blue band. Currently, the most common data courses are color aerial photographs and Landsat-TM images as demonstrated in this paper.