Citation
Abstract
A combined analysis merges 17,000 DSN Very Long Baseline Interferometric (VLBI) observations with 303,000 observations from the Crustal Dynamics Project (CDP) and the International Radio Interferometric Surveying (IRIS) project. Observations from the Radio Reference Frame Development (RRFD) and Time and Earth Motion Precision Observations (TEMPO) programs through late 1990 form the DSN VLBI data set. The combined analysis yields angular coordinates of extragalactic radio sources with a precision of a few nanoradians, as compared with 5- to 10-nrad precision for coordinates derived in the past solely from DSN data. The improvement in the combined analysis is due to the new Mark UI DSN data, as well as to Increased statistical strength from the large volume of observations from non-DSN experiments. Such a unified analysis is made possible by recent improvements in parameter estimation software efficiency. The terrestrial reference frame is based on joint VLBI experiments employing both DSN and CDP antennas, and on specifying the coordinates of VLBI antennas in a proper geocentric coordinate system by means of Global Positioning System (GPS) collocation of VLBI, LLR, and SLR (Lunar and Satellite Laser Ranging) sites. Approximately 200 sources, fairly uniformly distributed over the sky at declinations ranging from —45 to +90 deg, form the 1990-3 catalog, and show formal uncertainties smaller than 5 nrad. At this level of precision, it is critical to estimate corrections to the International Astronomical Union (I[AU) models of precession and nutation, and the 1990-3 source positions should only be used in conjunction with these corrections. Furthermore, at this level, a number of ignored effects, such as tropospheric turbulence and source structure, may cause errors equal to or greater than the formal uncertainties. Attempts to assess the influence of unmodeled systematic errors by comparing source positions with catalogs derived from independent analyses of partially independent data place a lower limit of 2 to 3 nrad on currently achievable accuracies. This leads to a realistic estimate of the true level] of accuracy of approximately 5 nrad for this combined radio source catalog.
Details
- Volume
- 42-106
- Published
- August 15, 1991
- Pages
- 364–383
- File Size
- 1.1 MB