Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis.

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.

Venus winds are zonal and retrograde below the clouds.

Winds in the lower atmosphere of Venus, inferred from three-dimensional radio interferometric tracking of the descents of the Pioneer day and north probes, are predominantly easterly with speeds of about 1 meter per second near the surface, 50 meters per second at the bottom of the clouds, and more than 200 meters per second within the densest, middle cloud layer. Between about 25 and 55 kilometers altitude the average flow was slanted equatorward, with superimposed wavelike motions and alternating layers of high and low shear.

Wind velocities on venus: vector determination by radio interferometry.

To determine the wind directions and speeds on Venus, as each Pioneer probe fell to the surface we tracked its motion in three dimensions using a combination of Doppler and long-baseline radio interferometric methods. Preliminary results from this tracking, coupled with results from test observations of other spacecraft, enable us to estimate the uncertainties of our eventual determinations of the velocity vectors of the probes with respect to Venus. For altitudes below about 65 kilometers and with time-averaging over 100-second intervals, all three components of the velocity should have errors of the order of 0.

Transcontinental baselines and the rotation of the Earth measured by radio interferometry.

Nine separate very-long-baseline interferometry (VLBI) experiments, carried out in 1972 and 1973 with radio telescopes 3900 kilometers apart, yielded values for the baseline length with a root-mean-square deviation about the mean of less than 20 centitneters. The corresponding fractional spread is about five parts in 10(8). Changes in universal time and in polar motion were also detertnined accurately from these data; the root-mean-square scatter of these results with respect to those based on optical methods were 2.