A demonstration of an independent-station radio interferometry system with 4-cm precision on a 16-km base line

The 1.24‐km base line vector between the two antennas of the Haystack Observatory was determined from X band radio interferometric observations of extragalactic sources via a new method that utilizes the precision inherent in fringe phase measurements. This method was employed in 11 separate experiments distributed between October 1974 and January 1976, each being between about 5 and 20 hours in duration. The rms scatters about the means for the vertical and the two horizontal components of the base line obtained from the 11 independent determinations were 7, 5, and 3 mm, respectively. The corresponding scatter for the base line length was 3 mm; the mean differed from the result obtained in a conventional survey by 8 mm, well within the 20‐mm uncertainty of the survey. (The determination of the direction from the survey was too crude to be useful.) Another external check on our data was possible, since the azimuth and elevation axes of one of the antennas do not intersect but are separated by 318 mm. We estimated this horizontal offset from the radio interferometry data and found a difference of 10 ± 9 mm from the directly measured value, the relatively large rms scatter being due to the ∼0.96 correlation between the estimate of this offset and that of the vertical component of the base line. Use of a newly completed calibration system in future experiments should allow the scatter to be reduced to the millimeter level in all coordinates for short base lines. For long base lines, such repeatability should be degraded only to about the centimeter level if calibrated observations with sufficient sensitivity are made simultaneously at two frequency bands. An assessment of the accuracy of either our present or future base line results awaits the availability of an accepted, more accurate, standard for comparison. Nonetheless, base line changes can be determined reliably at any established level of repeatability.

Section: Introductionmentioning

confidence: 99%

Geodesy by radio interferometry: Determination of a 1.24‐km base line vector with ∼5‐mm repeatability

Rogers¹,

Knight²,

Hinteregger³

et al. 1978

“…Before the technique of independent station interferometry, including portable antenna interferometry, can gain acceptance as a valuable geodetic-geodynamic measurement tool, a series of demonstration experiments is required to establish its reliability and accuracy at the few-centimeter level. Among the many possible demonstrations, a short-base line experiment is one of the most effective for several reasons, as is discussed in the work by Thomas et al [1976]. Briefly stated, short-base line interferometry experiments can lead to accurate threedimensional, earth-fixed base line measurements that more easily test the basic interferometer.…”

Section: ; Anderson Andmentioning

confidence: 99%

“…In addition to demonstrating portable station interferometry, the present experiments were motivated by the difficulties encountered in comparing survey and interferometry base lines during the analysis of the 16-km Goldstone experiments [Thomas et al, 1976]. The accuracy of that comparison was only about 20 cm as a result of possible interferometer instrumental instability and geoidal uncertainties in the survey.…”

Section: ; Anderson Andmentioning

confidence: 99%

“…Since other interferometry base line measurements [e.g., Cohen, 1972;Hinteregger et al, 1972;Ryle and Elsmore, 1973;Shapiro et al, 1974] have been summarized elsewhere [e.g., Thomas et al, 1976]; they will not be discussed in detail here. All previous interferometry experiments have utilized nonportable antennas that unfortunately lack the mobility that would be required in an extensive geodetic monitoring program.…”

Section: Introductionmentioning

confidence: 99%

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A demonstration of a transportable radio interferometric surveying system with 3-cm accuracy on a 307-m base line

Ong¹,

Macdoran²,

Thomas³

et al. 1976

Self Cite

A precision geodetic measurement system (Aries for Astronomical Radio Interferometric Earth Surveying) based on the technique of very long base line interferometry has been designed and implementedthrough the use of a 9-m transportable antenna and the NASA 64-m antenna of the Deep Space Communications Complex at Goldstone, California. A series of experiments designed to demonstrate the inherent accuracy of a transportable interferometer was performed on a 307-m base line during the period from December 1973 to June 1974. This short base line was chosen in order to obtain a comparison with a conventional survey with a few-centimeter accuracy and to minimize Aries errors due to transmission media effects, source locations, and earth orientation parameters. The base line vector derived from a weighted average of the measurements, representing approximately 24 h of data, possessed a formal uncertainty of about 3 cm in all components. This average interferometry base line vector was in good agreement with the conventional survey vector within the statistical range allowed by the combined uncertainties (3-4 cm) of the two techniques. ß ß / ß ß ß / ß ß / ß / ß ß ß ß

“…Over the last few years, considerable progress [e.g., Thomas et al, 1976;Rogers et al, 1978;Ryan et al, 1978;Niell et al, 1979;Herring et al, 1981] has been made toward realizing the potential of radio interferometry for measuring crustal motions and global rotations of the earth with accuracies at the centimeter level. Toward this goal a series of experiments, primarily with NASA's Deep Space Network (DSN) antennas, has been conducted over the last decade to develop two generations of very long baseline interferometric (VLBI) systems.…”

Section: Introductionmentioning

confidence: 99%

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

Sovers¹,

Thomas²,

Fanselow³

et al. 1984

Self Cite

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...