USNO Global VLBI Solution crf2006a
Presented here is the U.S. Naval Observatory's crf2006a 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 changes, 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), 3) a priori mean gradients computed from a GSFC Data Assimilation Office model for meteorological data from 1990-95, and 4) 5 degree elevation cutoff (versus 6 degree cutoff as was done for the ICRF). The solution also includes the most recent data and 8 years of VLBA RDV experiments (RDV01 to RDV53).
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 2006 January 19. This includes a total of 3939 diurnal sessions encompassing 4,665,274 measurements of group delay and delay rate. The weighted root-mean-square residuals of the solution were 24.035 ps in delay and 82.234 fs/s in delay rate. The SOLVE batch control file crf2006a_02.cnt.gz was used to generated this solution with an output spool file crf2006a_02.spl.gz. Tabulated below are the global and session values for the solution.
Source and Station Positions
Positions of 685 sources were estimated as global parameters. Positions for an additional 186 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 128 stations were estimated as local (session) parameters.
*Note: the complete set of 871 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 crf2006a source positions with the ICRF, ICRF-Ext.1, ICRF-Ext.2 and USNO crf2005c 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 crf2006a_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 ( crf2006a_01_pts1.cnt.gz, crf2006a_01_pts2.cnt.gz, crf2006a_01_pts3.cnt.gz, crf2006a_01_pts4.cnt.gz, crf2006a_01_pts5.cnt.gz, crf2006a_01_pts6.cnt.gz, crf2006a_01_pts7.cnt.gz, crf2006a_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.