Métodos digitais de obtenção de limiares topográficos de processos erosivos a partir de produto de radar

Abstract

Among the aspects of the studies of erosive processes, there is the proposition of topographic thresholds, given by an inverse relationship between contribution area (A) and slope (S), which conditions the surface runoff to cause gully initiation. The aim of this work was the study in the onset of gully erosion, using Alos/Palsar data. The study area was the watershed of the Ribeirão do Pântano, located in municipalities of Descalvado, Analândia e São Carlos (São Paulo state). The gully heads were identified in aerial images from the year 1988, as they are the oldest records found. Results indicate that the model from the radar is not free from noise and errors that may affect the proper extraction of information, requiring an initial treatment. For that, different treatment strategies were tested using the Focal Statistics tool, from ArcGIS 10.5 software to obtain morphometric parameters related to erosion processes in a more consistent way. The treatments were also applied to the Topographic Map data in some areas in the watershed, in order to analyze whether the radar data could be used as an alternative to the map. A correlation analysis between parameters A and S, obtained from both databases, it was possible to suggest the most proper treatment for the watershed, in addition to evidencing the ability of the Alos / Palsar to replace the Topographic Map, facilitating topographic threshold studies, which are scarce in our country. Using the treatment, the SxA index was applied to two sub-watersheds on the BHRP, with the higher concentrations of erosion processes on the same geological formation. The index obtained from the analysis in sub-watershed 1 was S = 0.0371A-0.4, and in sub-watershed 2 was S = 0.0297A-0.376, which were shown to be in accordance with the topographic threshold of other works carried out in Brazil, in places with similar characteristics of geology and land use, whose authors used Topographic Map data. In summary, the radar product proved to be efficient in the study of topographic threshold, which is fundamental in understanding the dynamics of the formation of erosive processes as an aid in territorial planning actions.