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Wednesday
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May 16, 2012
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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.
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.
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
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wrms histogram:
PS,
JPG
Chi2 histogram:
PS,
JPG
wrms vs. Chi2:
PS,
JPG
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| 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.
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