A comparison of synthetic aperture radar (SAR) parameters that are characteristic of airborne and orbital systems (e.g., SEASAT and SIR-A) indicates that the major advantage of airborne SAR is its inherent flexibility in matching image acquisition flight paths and altitudes to enhance the geologic "grain" of the terrain and the prevalent relief. The latter factor is particularly significant in low-relief areas, such as the Texas Gulf Coast. There, extensive SAR image coverage was acquired by flying the airborne system at a relatively low altitude, with the radar antenna tilted at a shallow angle. The combination of low altitude and antenna positioning provided a grazing illumination that highlighted, by shadowing, the otherwise subtle relief features in the resulting imag ry. A comparison of the SAR with Landsat imagery in a key area demonstrates how "featureless" the terrain appears when illuminated with an energy source in a higher position.

The illumination geometry-enhanced SAR imagery has been used to evaluate three areas in the Gulf coastal plain of Texas. These are, from east to west, an area of salt domes near Houston, an area of strong fractural control near Matagorda, and an area of serpentine plugs near Luling-Austin.

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