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Naval Meteorology and Oceanography Command U.S. Naval Observatory
Thursday November 23, 2017

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USNO Global VLBI Solution crfk2006a

Note: this is not a normal USNO solution but is a specialized solution with a specialized purpose and should only be used for such purpose.

Presented here is the U.S. Naval Observatory's crfk2006a global solution. The solution includes VLBA observations at 24 GHz (K-band) from 2002 May through 2005 August. A total of 8 diurnal sessions encompassing 57,936 measurements of group delay and delay rate were included*. Parameters estimated per session include twenty-minute piecewise linear continuous troposphere parameters; tropospheric gradients in the east-west and north-south directions, linear in time, estimated once per session; quadratic clock polynomials for the gross clock behavior; and sixty-minute piecewise linear continuous clock parameters. No ionosphere calibration was applied. ITRF2000 was used as a priori station positions and velocities. USNO Bulletin A (2006May03) was used as a priori EOP. Source positions were the only global parameters (i.e. parameters dependent on all observations) and were linked to the ICRF by constraining the right ascension and declination zero points to those of the ICRF Defining sources.

The weighted root-mean-square residuals of the resultant solution were 16.15 ps in delay and 42.40 fs/s in delay rate. The SOLVE batch control file crfk2006a_02.cnt.gz was used to generated this solution with an output spool file crfk2006a_02.spl.gz.

*These data are part of a joint NASA, NRAO, Bordeaux Observatory and USNO program to extend the ICRF to higher radio frequencies.

Source Positions

Positions of 250 sources were estimated as global parameters. A total of 12 sources with fewer than three good observationswere excluded from the solution.

Tabulated data.

Global source positions crfk2006a_02.sou_gsnoop.gz IERS format (gsnoop)
Global source positions crfk2006a_02.sou.gz format description

Plots.

Sky Distribution (Aitoff) PS JPG
Formal error histogram PS JPG
RA formal error: mean (median) 0.36 (0.11) mas
Dec formal error: mean (median) 0.78 (0.25) mas

Comparisons

Shown below are comparisons of the USNO crfk2006a source positions with the ICRF, ICRF-Ext.1, ICRF-Ext.2 and USNO crf2006a source positions. The weighted rms differences are at the end of the difference tables. In the vector difference 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. Note that the sigmas are based on the inflated errors for the ICRF and ICRF-Ext.1 comparisons. The sigmas are based on the formal errors for the ICRF-Ext.2 and the USNO frame comparisons.

Tabulated data and plots.

crfk2006a_02 minus ICRF Defining Difference Table Vector Plot: PS JPG
crfk2006a_02 minus ICRF-Ext.1 Difference Table Vector Plot: PS JPG
crfk2006a_02 minus ICRF-Ext.2 Difference Table Vector Plot: PS
Delta vs. RA: PS
Delta vs. Dec: PS
JPG
JPG
JPG
crfk2006a_02 minus crf2006a_02 Difference Table Vector Plot: PS JPG

Position Time Series

A total of 56 sources were observed in five or more sessions. To assess the position stability of these sources, four additional solutions were made with identical parameterization and data. In each of these solutions, one quarter of the 56 sources were estimated as "arc" parameters (i.e. an estimate of the position was derived for each session in which the sources were observed). The remaining sources were treated as global. Results are presented in the following tables and plots. In the position time series 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.

Weighted mean, wrms and reduced Chi2 Table wrms histogram: PS, JPG
Chi2 histogram: PS, JPG
wrms vs. Chi2: PS, JPG
Weighted mean positions Table IERS format (gsnoop)
Position time series PS (~400 KByte)
RA wrms: mean (median) 0.16 (0.13) mas; RA Chi2: mean (median) 5.0 (3.8) mas
Dec wrms: mean (median) 0.30 (0.22) mas; Dec Chi2: mean (median) 3.8 (2.8) mas

Shown below is a comparison of the source "arc" positions with their global positions. The weighted rms differences are at the end of the difference table. In the vector difference plot, green indicates a less than 3-sigma difference, orange indicates a 3-5 sigma difference and red indicates a greater than 5-sigma difference. Note that the sigmas are based on the formal errors.

crfk2006a_02 global minus "Arc" weighted mean Difference Table Vector Plot: PS, JPG

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