MAPEAMENTO DE LATERITAS MINERALIZADAS EM FERRO DO DEPÓSITO DE N1 (CARAJÁS-PA) ATRAVÉS DE CLASSIFICAÇÃO TEXTURAL DE IMAGENS DE RADAR DO SAREX'92.

Abstract

SAR imagery presents a high potential for geological applications in the moist tropic due to the topographic enhancement of the terrain and the all-weather sensing capability. As the terrain macro (slope variations) and micro-topography (roughness in the wavelength scale of the SAR) are highlighted in this imagery, textural attributes can be used for rock type and weathering product mapping. Texture describes the arrangement of spatial patterns or variations in tone within the image. The N1 iron deposit, located in the northern border of the Carajas Province, is related to an almost horizontal plateau with a lateritic cover showing sub-units closely related to the iron mineralizations and to specific savanna-type vegetation. The research was based on the airborne CV-580 C-band ( l = 5.6cm) SAR imageries with dual polarization (HH, VV) and distinct illumination geometry acquired during the SAREX’ 92 (South American Radar Experiment 1992 ). The SAR data set was analyzed through textural classifications derived from first and second order measures (Gray Level Co-occurrence Matrix) aiming at the mapping of the lateritic units. The comparison of the classified maps and the surficial geology has revealed that the use of SAR texture is still limited as an operational tool. However, textural SAR classification based on GLCM can be used as preliminary map of the spatial distribution of laterites for field verification. In situ surface roughness measurements were also important for the evaluation of the classification results and the texture attributes were sensitive to the sensor and target parameters.