Resumo

MARCHIONNI, Daniela S  e  CAVAYAS, François. Radar remote sensing as a source of structural and lithological information: RADARSAT-1 SAR spatial image analysis. Geoacta [online]. 2014, vol.39, n.1, pp.62-89. ISSN 1852-7744.

In recent years, radar imagery has become a frequently used tool for geological information extraction as more numerous radar remote sensing systems that make available a great variety of images of great utility to geological mapping have become available. Given these radar systems’ observation geometry (side viewing) and signal nature (active microwave), the data acquired by these radar sensors are substantially different from those obtained by optical sensors, making them able to be considered as a complementary information sources. The processes involved in the formation of radar imagery are highly dependent on the properties of the radar beam in terms of both the signal character (frequency and polarization) and the observation geometry (incidence angle, look direction). The satellites carrying on-board radar sensors can acquire images in either ascending or descending orbit and in either right- or left-looking directions as well as with different inclination angles (thus varying illumination conditions). Therefore images of the same area taken by different systems can provide very different information. Thus, determining the criteria for image selection for a particular application is an essential step. The microwave’s sensitivity to dielectric properties, moisture content and surface roughness, particularly in relationship to the wavelength of the radar beam, will be reflected in the images tone and texture since these factors directly affect the signal intensity. Radar sensors can highlight subtle morphological variations in an outcrops’ micro topography even when its size is below the limit of the spatial resolution of the imagery. The terrain morphology (its slope and aspect) will have a significant impact on the return signal since it affects the local radar beam incidence angle. Moreover, the side-viewing geometry will benefit the identification of lineaments and structural features in general when they have a morphological expression and if their observation is enhanced by the radar beam illumination. Given the great variability of the factors involved in formation of a radar image, and given how all these factors interact with the characteristics of the imaged area, all these elements must be taken into account to faithfully interpret the geological characteristics of a particular territory. The basis and results of some analyses of the potential of radar imagery to manifest lithological variations and to benefit the detection of structural and morphological features are presented here.

Palavras-chave : Radar systems; Spatial analysis; Morphology; Lithology; Structures.

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