USNO Global VLBI Solution crf2002a
Presented here is the U.S. Naval Observatory's crf2002a global solution. Parameterization of this solution follows that of the International Celestial Reference Frame (ICRF) solution (Ma et al. 1998, AJ, 116, 516) but includes several analysis improvements, the most important of which are 1) using the Niell Mapping Function to model the troposphere, 2) more frequent estimation of troposphere gradients (once every 6 hours instead of once every 24 hours as was done for the ICRF) and 3) a priori mean gradients computed from a GSFC Data Assimilation Office model for meteorological data from 1990-95. The solution also includes more than 7 years of new data (including most of the VLBA RDV experiments from RDV01 to RDV33).
The resultant global SOLVE solution includes most available VLBI observations at 8.4 GHz (X-band) and 2.2 GHz (S-band) from 3 August, 1979 through 30 May, 2002. This includes a total of 3338 diurnal sessions encompassing 3,393,677 measurements of group delay. The weighted root-mean-square residuals of the solution were 22.869 ps in delay (delay rate was not used in the solution). The SOLVE batch control file crf2002a_02.cnt.gz was used to generated this solution with an output spool file crf2002a_02.spl.gz. Tabulated below are the global and session values for the solution.
Source and Station Positions
Positions of 577 sources were estimated as global parameters. Positions for an additional 144 sources (including 3 radio stars) were estimated for each session independently as local parameters. A total of 77 sources with either no good observations or with bad data were excluded from the solution. Positions of all 122 stations were estimated as local (session) parameters.
*Note: the complete set of 721 source positions can be obtained by down-loading these two files. The positions for the local sources are weighted mean positions. The position uncertainties for the local sources are the weighted root-mean-square deviations from the weighted mean positions.
Earth Orientation Parameters
Daily nutation offsets in longitude and obliquity were estimated for each session separately.
Shown below is a comparison of the USNO crf2001a solution with the ICRF Ext.1 source positions. The weighted rms differences are at the end of the difference tables.
Tabulated data and plots.
Position Time SeriesThree additional solutions were made with identical parameterization and data as for crf2002a_02. In each of these three solutions, one third of the sources were estimated as "arc" parameters (all other sources were treated as global). The SOLVE BATCH control files for these additional solutions are available here (crf2002a_pts1.cnt.gz, crf2002a_pts2.cnt.gz, crf2002a_pts3.cnt.gz). Daily nutation offsets in longitude and obliquity were estimated for each session separately. Results are presented in the following tables.
Tabulated statistics and plots.