DETERMINING HEIGHTS AND SLOPES OF FAULT SCARPS AND OTHER SURFACES ON VENUS USING MAGELLAN STEREO RADAR

This report presents relationships and techniques for determining the heights and slopes of discretely dipping surfaces, such as normal faul t scarps, on the surface of Venus from measurements of their widths in Magellan stereo synthetic aperture radar (SAR) images. These surfaces are clearly recognizable as distinct bands of increased or decreased radar backscatter relative to flat-lying areas in the 120 to 280-m res olution Magellan SAR images, but are not generally imaged in the >10-k m resolution Magellan altimetry. Our methods take into account radar d istortion effects, and allow one to determine whether a slope is fores hortened, laid over, elongated, or in radar shadow. The techniques mak e use of graphs constructed for the Magellan incidence angle profiles so that investigators can determine the local height and slope of an i ndividual surface in a straightforward manner, but the techniques are applicable to any stereo radar data set if the radar incidence angles are known. Additionally, the techniques can be used to improve digital elevation models constructed using radar stereoscopy in areas that ha ve steep local terrain where stereoscopic fusion may be impossible due to the effects of layover or radar shadow. Using these techniques we show that there are normal fault scarps on Venus with heights in the 7 00-m range that have remarkable topographic slopes of close to 60 degr ees, something unheard of on Earth and which suggests a high effective cohesive strength of the Venusian crust.