Avaliação do desempenho de índices espectrais na identificação de áreas desertificadas

Abstract

The NDVI, TGSI, Albedo, bare soil line, Tasseled Cap and Thermal index are essential for terrestrial surface mapping and are important for desertification studies. The hypothesis was that spectral indexes from remote sensing images allow the identification and mapping of desertification. NDVI, TGSI, Albedo, Soil Line, Tasseled Cap and Thermal were applied to the Irauçuba Centro Norte desertification area, FLONA and the exclusion areas from 2000 to 2008. The TM sensor images of the USGS platform, path / row (217/063; 218/062; 218/063, from the end of the rainy season and the end of the dry period of 2000, 2001, 2003, 2004, 2005, 2006, 2007 and 2008; Flaash and geometric correction with Landsat 08 image. Mosaic of the scenes and cut of the areas of interest was done. To identify and evaluate desertification, range were used for each index, according to the literature. NDVI values were compatible with desertified areas in the Irauçuba Centro Norte desertification area, FLONA and exclusion areas. The TGSI indicated the presence of sand in superior amounts in relation to the silt and clay in all the studied areas. The albedo presented values compatible with desertified areas in the desertification field and in the exclusion areas. In relation to FLONA, the albedo was reduced due to the presence of residues and water bodies presenting values compatible with non-desertified areas. The bare soil line indicated sparse vegetation in all studied areas. The Tasseled Cap Brightness transformation indicated greater clustering of pixels around its axis, while greater dispersion around the Greenness axis was observed in all areas studied during all periods of the time series. The surface temperature presented reduced values in times of good vegetation cover, however, in all the studied areas, values of temperatures compatible with exposed soils were verified. The interaction between the NDVI, TGSI and Albedo in the core and FLONA, were presented in a radar-type graph, indicating the relation between them. Stacking of the data was performed and there was no change in the indices over the years studied, denoting the occurrence of desertification. With the analysis of the results, it can be concluded that the NDVI, TGSI, Albedo, bare soil line and Tasseled Cap indexes allowed the identification and mapping of desertification in the Irauçuba Center North desertification area and in the exclusion areas and the susceptibility of FLONA to desertification