This book will occupy a prominent place on the shelves of many students and geologists who will analyze the Venus radar data acquired by the Magellan spacecraft. Because the Magellan images are so well documented here and in other Magellan Project documentation cited herein, it is likely that Magellan data will serve as training material for Earth studies. It is an enormous data set; the Magellan Mission had the daunting task of mapping all of Venus, which is nearly Earth size but with no obscuring ocean basins. In the early phases of mission planning over a decade ago, radar interpretation as applied to the understanding of geologic features was an infant science. Most planetary scientists were accustomed to interpreting conventional optical images, and few were familiar with the peculiarities of radar images. Today there are many more scientists who are expert in using radar data, but there will long remain a strong need for the information in this book, even for those of us who feel that we know all the foibles of the Magellan data sets.
An overview of Magellan Mission requirements, radar system characteristics, and methods of data collection is followed by a description of the image data, mosaic formats, areal coverage, resolution, and pixel DN-to-dB conversion. The availability and sources of image data are outlined. Applications of the altimeter data to estimate relief, Fresnel reflectivity, and surface slope, and the radiometer data to derive microwave emissivity are summarized and illustrated in conjunction with corresponding SAR image data. Same-side and opposite-side stereo images provide examples of parallax differences from which to measure relief with a lateral resolution many times greater than that of the altimeter. Basic radar interactions with geologic surfaces are discussed with respect to radar-imaging geometry, surface roughness, backscatter modeling, and dielectric constant.
Techniques are described for interpreting the geomorphology and surface properties of surficial features, impact craters, tectonically deformed terrain, and volcanic landforms. The morphologic characteristics that distinguish impact craters from volcanic craters are defined. Criteria for discriminating extensional and compressional origins of tectonic features are discussed. Volcanic edifices, constructs, and lava channels are readily identified from their radar outlines in images. Geologic map units are identified on the basis of surface texture, image brightness, pattern, and morphology. Superposition, cross-cutting relations, and areal distribution of the units serve to elucidate the geologic history.
218 pages, over 75 photos and illustrations, many in color.
