Abstract

In the tropical semi-arid environment of Brazil geological applications with radar are still rare. The objective of this research was the evaluation of multipolarized L-band radar images acquired by the sensor SAR-R99B (SIVAM-CENSIPAM) for geological mapping in the lower Curaca valley, an important Cu-rich district of the Bahia state. The test-site is characterized by a flat terrain, with moderate to sparse caatinga vegetation and shallow residual soils closely related to changes in the geological substratum. These characteristics favor the evaluation of SAR images for geological mapping. The test-site is part of the Sao Francisco Craton, and encompasses paleoproterozoic granulitic and gneissic rocks and an intrusive sequence of mafics and ultramafics. Subordinately, metasediments with neoproterozoic ages also occur. In this investigation it was evaluated multipolarized L-band images (L-HH, L-VV, L-HV), amplitude format with 6-meter of spatial resolution. The photogeological procedures were applied using the graphical interface of viewing and digital enhancements available in the FOCUS package (PCI Geomatics software), calibrated with bibliographic and field information. The results of the photogeological interpretation showed that L-VV presented the best performance in the discrimination of lithologies given by a higher tonal/textural contrast of more frequent units (mica- schists, quartz-feldspar gneiss) and a better detailment of more restricted ones (marbles, mafic-ultramafics). Regarding the structural characterization, the three polarizations showed a similar performance, with a slightly disadvantage of L-HH revealing the importance of the vertical component of polarization in the L-VV and L-HV images in the enhancement of structural features. The excellent radiometric quality of calibrated SAR data, high spatial resolution and good response sensitivity to variations of macro, micro-topography and moisture were responsible for the results of the analysis.

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