Radio interferometric determination of intercontinental baselines and Earth orientation Utilizing deep space network antennas: 1971 to 1980

Abstract

A series of experiments has been conducted during the last decade to develop a radio interferometry system capable of measuring crustal and rotational motions of the earth, as well as source positions for a reference frame based on compact extragalactic radio sources. With the exception of one session between Big Pine, California, and Westford, Massachusetts, the observing stations have been those of NASA's Deep Space Network in California, Spain, and Australia. Approximately 2400 observations of extragalactic radio sources were made between August 1971 and February 1980 during 48 separate sessions. A single multiparameter fit was applied to the observed values of delay and delay rate to extract astrometric and geophysical parameters from this decade-long sequence. The fit produced estimates of 684 parameters, including station locations, radio source positions, polar motion, universal time, the precession constant, and solid earth tides. The a priori model included gravitational bending, the 1980 International Astronomical Union (IAU) nutation series, the 1976 IAU expressions for Greenwich mean sidereal time and precession, Bureau International de l'Heure estimates of universal time and polar motion, and monthly mean values for zenith troposphere delay. The rms residuals were 0.52 ns for delay and 0.30 ps/s for delay rate. Intercontinental baseline lengths have been determined with formal uncertainties of 4 to 10 cm. Universal time and polar motion were measured at 49 epochs, with formal uncertainties (for the more recent data) of 0.5 ms for UT1 and 6 and 2 millis6conds of arc (mas), respectively, for the X and Y components of polar motion. Our 1971-1980 data produced an estimate of the lunisolar precession constant that is smaller than the 1976 IAU value by 3.8 mas/yr with an approximate accuracy (la) of 2 mas/yr. The earth tide results agree with the commonly accepted values.Goldstone, California, and at Madrid, Spain), on a transcontinental baseline (Big Pine, California, to Westford, Massachusetts), and on two intercontinental baselines (Goldstone, California, to Madrid, Spain, and Goldstone, California, to Tidbinbilla, Australia). A single multiparameter fit has been made to this decade-long sequence of observations to extract significant astrometric and geophysical parameters. The adjusted parameters included station locations, source positions, polar motion, universal time, the precession constant, the Love numbers and phase angle for the solid earth tides, and the gamma factor of relativity theory. This paper outlines the techniques and analysis of these experiments and presents results of geophysical significance. A paper presenting the radio source positions is in preparation.In interferometry measurements the random broadband emission of an extragalactic radio source is simultaneously recorded at two widely separated radio antennas. Cross correlation of the recorded data at a central site leads to a determination of the difference in arrival times of the radio wave front at the two antennas. Since thi...

Geocentric Terrestrial Reference Frame Accuracy: DSN Spacecraft Tracking and VLBI/Lunar Laser Ranging

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