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Ford, P. G.

Publications and source records attributed to Ford, P. G..

23 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Pioneer Venus radar results - Altimetry and surface properties

A topographic map of 93% of the Venus globe was depicted by the radar altimeter of the Pioneer Venus orbiter with a resolution better than 150 km. Extremes in relief expressed as a center-of-mass-to-surface radius extend from 6049 to 6062 km; the elevated terrain is dominated by a massive equatorial area equal in size to South America. The distribution of average meter-scale surface slopes is determined for the same regions in the 1 to 10 deg range; elevated areas have higher slopes, so that most features observed in the earth-based images are also evident in the vertical-incidence spacecraft measurements.

Pettengill, G. H.↗
NASA NTRS1979

Synchronization of clocks by very-long-baseline interferometry

Two hydrogen-maser clocks, one at Haystack Observatory and one at the National Radio Astronomy Observatory, were synchronized by means of observations of several extragalactic radio sources on March 28, and again on September 23, 1977. Observations were made sequentially in eight 360-kHz bands distributed between about 8.4 and 8.5 GHz with spacings designed to enable the group-delay difference between the signals received at the two observatories from a given source to be estimated unambiguously, within an uncertainty of less than 1 ns set by receiver noise. The epoch and the rate differences between the observatories' clocks for each experiment were estimated by analysis of observations that spanned several hours. The application of corrections for the contributions to the delays of the antennas, feeds, receiver systems, and recorders yielded absolute determinations of the clock epoch differences. During each experiment, portable cesium clocks were flown from the U.S. Naval Observatory to the observatories and back. The traveling-clock data, analyzed in each case after the VLBI synchronization had been completed, confirmed the VLBI results to within 18 and 14 ns for the first and second experiments, respectively.

Clark, T. A.↗
NASA NTRS1979

Venus - Preliminary topographic and surface imaging results from the Pioneer Orbiter

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 km above the surrounding terrain. Two of these features, one bright and the other dark, lie adjacent to each other astride the 65 N parallel between longitudes 310 E and 10 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 N, 283 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.

Pettengill, G. H.↗
NASA NTRS1979

Pioneer Venus radar mapper experiment

Altimetry and radar scattering data for Venus, obtained from 10 of the first 13 orbits of the Pioneer Venus orbiter, have disclosed what appears to be a rift valley having vertical relief of up to 7 kilometers, as well as a neighboring, gently rolling plain. Planetary oblateness appears unlikely to exceed 1/2500 and may be substantially smaller.

Pettengill, G. H.↗