Discriminacao de lateritas mineralizadas em ferro no deposito de N1 (Carajas-PA) por radar imageador: uma avaliacao atraves de classificacao textural / Discrimination of iron ore laterites in the deposit N1 (Crajas - PA) using radar imagery: an evaluation through textural classification

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

The use of imaging SAR presents a high potencial for geological applications in cloudy cover regions, such as the Brazilian Amazon, due to the side viewing geometry and the longer wavelengths, which result in the enhancement of the terrain and the all-weather sensing capability. As the macro and micro topography are normally highlighted in the Syntetic Aperture Radar (SAR) imagery, textural attributes extracted from this kind of data are important in geological applications such as rock alteration products discrimination and structural studies. The textures describe the arrangement of spatial pattern or the variation frequency of tonal values within a region in the scene. The association of minor features, too small to be detected individually, but which allow the identification and delimitation of areas with specific superficial properties, provides this spatial distribution. Within this context, a SAR geological investigation was carried out in the N1 iron deposit, located next to the northern border of the Carajás Mineral Province (Brazilian Amazon region). The test-site is characterized by an extensive lateritic cover, with sub-units closely related to the iron mineralizations and a specific low dense savanna-type vegetation (campus rupestres). The research was based on the airborne C-HH/VV SAR data (Narrow and Nadir Modes) acquired during the SAREX92 (South America Radar Experiment) campaign and also a RADARSAT-1 scene (Fine Mode, Beam 4) collected as part of the ADRO (Application Development and Research Opportunity) program. The SAREX Nadir Mode fligh was oriented parallel to the RADARSAT-1 ascending orbit. The Narrow Mode scene was acquired almost orthogonal to the dominant NW-SE geological trend in the area. The SAR data, with distinct illumination geometry, radiometry and spatial resolution, were digitally analysed through texture feature classification approaches derived from first and second order measures (grey level co-ocorrence matrix) aiming at the superficial mapping of the lateritic units. Roughness measures collected in the field were also important for the evaluation of the classification results. The investigation has shown that texture SAR attributes can be used for laterite mapping purposes based solely on the airborne data. The classification performance for the RADARSAT-1 data was considered poor. While general conclusions on the sensitivity of textural features to the SAR systems and the geometry of the the acquisition, mainly the azimuth and subordinately, the incidence angles, can made from the results of this study, there is a need to further refine these conclusions. Specifically it is recommended to evalue additional approaches to reduce RADARSAT-1 scene speckle through averaged images previously to the texture classification, and also to test additional classifier such as semi-variogram and segmentation.

ASSUNTO(S)

radarsat 1 ferro cobertura lateritica geologia carajás (pa) rugosidade projeto sarex radar de abertura sintética sar imagens de radar análise de texturas programa adro

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