Abstract
Tone and texture on synthetic-aperture radar (SAR) images acquired from the Seasat satellite enhance the topography of the heavily forested Valley and Ridge area in the southern Appalachians. Mapping from the radar images provides topographic information which serves for making lithologic and structural interpretations. The radar selectively suppresses drainage features and geomorphic lineaments of low relief, whose strike direction is within 15° of the direction of radar illumination. This shortcoming is compensated partly by the dual directions of scene illumination obtainable with the Seasat imaging system.
Perception of geomorphic lineaments on the Seasat radar images is greater than on corresponding Landsat multispectral scanner (MSS) images by a factor of about 2, though the radar system introduces two types of geometric distortion that do not occur on the MSS images. Short linear features tend to be rotated on the radar imagery, and steep slopes are excessively compressed toward the imaging direction owing to radar layover. The preferred orientations of short, geologically uncorrelated lineaments are more readily interpreted from the Seasat radar data. The observed coincidence of some uncorrelated lineaments with reported magnetic and gravitational trends in the basement, the alignment with known structural features, and the orthogonal relations of certain lineaments revealed from the radar images provide a basis for further detailed geologic study.
The excessive geometric distortion of sloping topography on the Seasat radar images due to layover is largely a function of the Seasat imaging geometry. The low inclination of the imaging radar beam from vertical produces layover of all slopes that exceed about 20°. Airborne radar images acquired with the same illumination direction as the Seasat images, but with a much higher inclination of the imaging beam from vertical, provide equivalent enhancement of the topography with virtually no distortion due to layover. Difference in wavelength and image resolution between the Seasat and the airborne imaging radars are insignificant factors relative to the geometric distortion due to layover. On future orbital imaging radars the advantages of terrane enhancement can be retained and the disadvantages of geometric distortion can be significantly reduced by utilizing a more highly inclined viewing geometry.
