ABSTRACT: High-Resolution Topographic Measurements from Magellan Data

KIRK, RANDOLPH L., U.S. Geological Survey, Flagstaff, AZ

The high-resolution radar images of Venus returned by the Magellan spacecraft have proved enormously useful as a starting-point for geologic interpretation of the events that have shaped that planet's surface, but, as is true for the Earth, the interpretive process is greatly abetted by detailed knowledge of the surface relief. The

Magellan altimetry data (resolution 10-20 km) are useful in this regard, but topographic measurements at or near the image resolution are even more valuable. Such measurements are being obtained in a variety of ways. Radarclinometry, or "shape-from-shading," can be used to derive surface relief from a single image, but it can be fooled by variations in the radar-scattering properties of the surface, misinterpreting them as slope variations. Interferometry is a powerful tool that can measure the elevation of each image pixel to an accuracy of centimeters, but it can be applied only if the spacecraft returns to almost the exact point from which an earlier image was acquired, e.g., where successive orbits cross near the poles, and perhaps fortuitously at lower latitudes. Both of these me hods directly yield topographic models from which synthetic stereo pairs can be generated. Magellan will also obtain real stereo pairs: Its third cycle of mapping Venus will be devoted primarily to obtaining "right-eye-views" complementary to the images obtained in the first cycle. Such views from eight test orbits have already proved to be the highest quality stereo radar data ever generated. A major challenge, given the sheer volume of data to be obtained, will be the creation of quantitative topographic maps from the stereo images. Various approaches to this problem are being pursued, ranging from conventional compilation by technicians using analytic stereoplotters to automated image matching on a computer.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)