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Naval Meteorology and Oceanography Command U.S. Naval Observatory
Tuesday September 19, 2017

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USNO Global VLBI Solution crf2004a

Presented here is the U.S. Naval Observatory's crf2004a 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, accepted for publication) 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 8 years of new data (including 42 VLBA RDV experiments from RDV01 to RDV42).

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 2004 March 6. This includes a total of 3630 diurnal sessions encompassing 4,021,910 measurements of group delay and delay rate. The weighted root-mean-square residuals of the solution were 24.099 ps in delay and 78.309 fs/s in delay rate. The SOLVE batch control file crf2004a_02.cnt.gz was used to generated this solution with an output spool file crf2004a_02.spl.gz. Tabulated below are the global and session values for the solution.

Source and Station Positions

Positions of 656 sources were estimated as global parameters. Positions for an additional 182 sources (including 3 radio stars) were estimated for each session independently as local parameters. A total of 80 sources with either no good observations or with bad data were excluded from the solution. Positions of all 125 stations were estimated as local (session) parameters.

Tabulated data.

*Global source positions crf2004a_02.sou_gsnoop.gz IERS format (gsnoop)
Global source positions crf2004a_02.sou.gz format description
Local source positions crf2004a_02.lso.gz format description
*Local source positions (weighted mean & wrms) crf2004a_02.sou_gsnoop_wrms.gz IERS format (gsnoop)
Local baseline vectors crf2004a_02.bas.gz format description

*Note: the complete set of 838 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.

Tabulated data.

EOP time series, IVS format crf2004a_02.eob.gz format description
Nutation angles crf2004a_02.nut.gz format description

Comparisons

Shown below are comparisons of the USNO crf2004a source positions with the ICRF Ext.1 and USNO crf2003b source positions. The weighted rms differences are at the end of the difference tables.

Tabulated data and plots.

crf2004a_02 minus ICRF Ext.1 Defining Difference Table Aitoff Plot: PS, JPG
crf2004a_02 minus ICRF Ext.1 Difference Table Aitoff Plot: PS, JPG
crf2004a_02 minus crf2003b Difference Table Aitoff Plot: PS, JPG

Position Time Series

Three additional solutions were made with identical parameterization and data as for crf2004a_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 (crf2004a_01_pts1.cnt.gz, crf2004a_01_pts2.cnt.gz, crf2004a_01_pts3.cnt.gz). Daily nutation offsets in longitude and obliquity were estimated for each session separately. Results are presented in the following tables.

Tabulated data.

crf2004a_pts1 Nutation angles crf2004a_01_pts1.nut.gz format description
crf2004a_pts2 Nutation angles crf2004a_01_pts2.nut.gz format description
crf2004a_pts3 Nutation angles crf2004a_01_pts3.nut.gz format description

Tabulated statistics and plots.

Min obs/pos: 1; Max Sigma/pos: NONE (i.e. all data)
Wrms Table; "arc" wrms and Chi^2/df (df=degree of freedom)
Positions Table in IERS (gsnoop) format; "arc" weighted mean and wrms
"Arc" Position Plots (PS, one file ~10 MByte)
Min obs/pos: 3; Max Sigma/pos: 1 mas
Wrms Table; "arc" wrms and Chi^2/df (df=degree of freedom)
Positions Table in IERS (gsnoop) format; "arc" weighted mean and wrms
"Arc" Position Plots (PS, one file ~8 MByte)

crf2004a_02 global minus "Arc" weighted mean Difference Table Aitoff Plot: PS, JPG

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