title: Venus: preliminary topographic and surface imaging results from the pioneer orbiter.
abstract: Three large Venus surface features, identified previously in images obtained from Earth-based radar observations, are shown by the Pioneer Venus radar mapper to be elevated 5 to 10 kilometers above the surrounding terrain. Two of these features, one bright and the other dark, lie adjacent to each other astride the 65 degrees N parallel between longitudes 310 degrees E and 10 degrees E. The combined region forms a huge tectonically uplifted plateau, surmounted by radar-bright ridges that may have either a volcanic or tectonic origin. The third feature, located at 30 degrees N, 283 degrees E, is radar-bright and may consist of volcanic material extruded along a fault zone. A first radar-scattering image, compiled from data obtained by the mapper in its imaging mode, shows a region north of the equator; several circular depressions seen in this area may result from meteoritic impact.
authors.forename: G H
authors.initials: GH
authors.lastname: Pettengill
authors.forename: P G
authors.initials: PG
authors.lastname: Ford
authors.forename: W E
authors.initials: WE
authors.lastname: Brown
authors.forename: W M
authors.initials: WM
authors.lastname: Kaula
authors.forename: H
authors.initials: H
authors.lastname: Masursky
authors.forename: E
authors.initials: E
authors.lastname: Eliason
authors.forename: G E
authors.initials: GE
authors.lastname: McGill