USNO Global VLBI Solution crf2005c
Presented here is the U.S. Naval Observatory's crf2005c global solution. Parameterization of this solution follows that of the International Celestial Reference Frame (ICRF) solution (Ma et al. 1998, AJ, 116, 516) and its extensions (Fey et al. 2004, AJ, 127, 3587) 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 the most recently taken data and 8 years of VLBA RDV experiments (RDV01 to RDV51).
The resultant global SOLVE solution includes most available VLBI observations at 8.4 GHz (X-band) and 2.2 GHz (S-band) from 1979 August 3 through 2005 September 12. This includes a total of 3874 diurnal sessions encompassing 4,435,016 measurements of group delay and delay rate. The weighted root-mean-square residuals of the solution were 23.750 ps in delay and 80.272 fs/s in delay rate. The SOLVE batch control file crf2005c_02.cnt.gz was used to generated this solution with an output spool file crf2005c_02.spl.gz. Tabulated below are the global and session values for the solution.
Source and Station Positions
Positions of 676 sources were estimated as global parameters. Positions for an additional 194 sources (including 2 radio stars) were estimated for each session independently as local parameters. A total of 83 sources with either no good observations or with bad data were excluded from the solution. Positions of all 126 stations were estimated as local (session) parameters.
*Note: the complete set of 870 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 are comparisons of the USNO crf2005c source positions with the ICRF, ICRF-Ext.1, ICRF-Ext.2 and USNO crf2005b source positions. The weighted rms differences are at the end of the difference tables. In the plots, green indicates a less than 3-sigma difference, orange indicates a 3-5 sigma difference and red indicates a greater than 5-sigma difference.
Tabulated data and plots.
Position Time SeriesEight additional solutions were made with identical parameterization and data as for crf2005c_02. In each of these solutions, one eighth 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 ( crf2005c_01_pts1.cnt.gz, crf2005c_01_pts2.cnt.gz, crf2005c_01_pts3.cnt.gz, crf2005c_01_pts4.cnt.gz, crf2005c_01_pts5.cnt.gz, crf2005c_01_pts6.cnt.gz, crf2005c_01_pts7.cnt.gz, crf2005c_01_pts8.cnt.gz ). Daily nutation offsets in longitude and obliquity were estimated for each session separately. Results are presented in the following tables and plots. In the plots, green indicates a less than 3-sigma difference, orange indicates a 3-5 sigma difference and red indicates a greater than 5-sigma difference.
Tabulated statistics and plots.