[IGSREPORT-15529] Wk 1445 MIT T2 Analysis Report
Tom Herring
tah at mtglas2.mit.edu
Wed Oct 3 05:02:07 PDT 2007
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IGS Electronic Report 03 Oct 04:53:07 PDT 2007 Message Number 15529
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Author: Thomas Herring
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MIT ANALYSIS REPORT GPS-WEEK 1445 Dates: 07sep16 to 07sep22
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MIT (Massachusetts Institute of Technology)
Room 54-618
77 Massachusetts Avenue,
Cambridge, MA 02139
e-mail: tah at mit.edu
tel: (617)253-5941 (Tom Herring)
fax: (617)253-1699
PRODUCTS GENERATED:
The following products are generated and uploaded into CDDIS @ NASA/GSFC
MIT1445g.SNX Combined sinex file from all available analysis centers
MIT1445g.SUM Name of this summary file
MIT1445g.RES File of the individual AC position estimates residuals
to the combined solution for the week.
0.0 Starting Week 1431, we changed the center weighting scheme. The results
from each center are compared to results from the combination of all
other centers. The RMS difference between the N and E components of the
common sites is used to scaled the covariance matrix to be consistent
with this RMS. An additional factor of 2 in variance is applied to all
centers to have, on average, the same scaling before the change.
0.1 Starting Week 1420, we dropped JPL from the combination due to the many
meta data errors that are not correctly reported in their sinex file.
Even with downweighting this solutions, the bad antenna errors, which
can be over 1 meter, are corrupting the combination.
1.0 Starting Week 1400 adopted the IGS05 apriori coordinate file and the
reference ststions in the list.
1.1 Starting Week 1386 ESA re-instated into combinations. The problems
with the sinex files seem to have been resolved.
1.2 Starting Week 1385 we started downweighting the ESA solution in the
combination because it is corrupting the combination. The problem
started in Week 1376 with a rapid increase in the RMS fit of the ESA
solution to combination from ~2mm horizontal to ~7mm horizontal. At
the same time, the RMS fit of the other centers in the combination increased
from ~1mm to ~2mm. Downweighting the ESA solutions, restored the fits of
the other centers to their pre-Week 1376 values.
1.3 Starting Week 1244 we adopted the 99 IGS reference sites in
IGS03P33_RS99.snx. System denoted as IGb00.
1.4 Starting Week 1203 we changed the method used to compute the variance
scaling for each sinex file. The old method is described in item 2 of
the analysis procedures below. In the new method, we determine the scaling
factor by the ratio of the adjustments to the IGS00 frame from a loose,
rotated and translated solution, to the sigmas determined for the adjustment.
The new method is robust when some of the reference sites have changed
position (because of outlier detection during the rotation/translation
step) and is not senstive to any aproiri rescaling factors used in the
analysis.
1.5 Starting Week 1202 adopted IGS01P37_RS54 for reference frame. Dropped
KOKB and FAIR from frame definition.
1.6 Starting Week 1125, we removed AREQ from the sites used in determining
the variance re-scaling of the center SINEX files. This site
appears to have moved by 0.5 meters at around week 1120.
1.7 Starting Week 1110, we stopped applied a pole-tide correction to
SIO sinex files because this correction is already made in their
analysis.
1.8 Starting Week 1066, we adopted the IGS realization of the ITRF97
(referred to as IGS97). We also replaced our constrained solution
a loose solution with translation (+-1 mm) and orientation (+-0.1 mas)
constraints applied.
1.9 Starting Week 1020, we adopted the ITRF97 reference frame
2.0 Starting Week 1002, we re-ordered the summary to give the residual
summary and the SINEX file errors first.
CENTER SINEX ERRORS: (corrected during processing).
CNT Site Type of Error Used values IGS.SNX values
HISTORY and PROCEDURES
----------------------
0.0 Starting Week 998 we adopted full checking of the center sinex
headers and we correct the solutions for differences between the
headers and a modified version of IGS.SNX. (The modifications are
to put full precision antenna L1/L2 offsets and to correct the WUHN
entry. The station log for this site shows height to BCR not ARP).
A new error reporting block has been added below. We also have
removed some of the routine documention in this summary.
0.1 Starting week 993 we started to add corrections for the pole-tide to
the SIO, NGS, and ESA sinex. According to the analysis descriptions
none of these centers apply the pole tide correction. Starting with
the re-submission of week 992, we corrected the LOD values in JPL sinex
files from regularized LOD (should be called LODR in the SINEX file)
to standard LOD. (Since starting multiday polar motion combinations
we have been correcting the sign error in the JPL LOD values.
0.2 Starting week 989 we include as Section 5.0 of this summary, the
Earth rotation parameter estimates from the constrained combination
solution in the IERS format.
0.3 Starting Week 980 we include multiday polar motion/UT1 estimates into
our analysis. We also no longer need to deconstrain the AC sinex
files although to add back into the covariance matrices at rotational
uncertainity which is coupled between station positions and EOPs.
0.4 Starting Week 0943 we base the analysis on the ITRF96 system and the
reference site list for the ITRF96 system. The increase in the number
of sites used to obtain analysis variances increases the variance
factors for all centers by factors between 2 and 4. The Chi**2 for
the center residuals is now much closer to 1.0
0.5 Starting Week 0931 we added a new residual file to our submissions.
A description of the contents of the file is given in the file itself.
We also changed the treatment of the translation of the individual
AC solutions. The generation of the weighting factors and the constrained
combined solution remains unchanged. However, in the unconstrained
analyses (used for AC comparisons) we now allow explicit translation
and scale parameters in the solution. The net effect is to generate
more realisitic sigmas for the center of mass position estimates and to
make the coordinate estimates immune to real center of mass translations
and scale changes.
0.6 Starting Week 0901 we started using a new apriori file not Non-ITRF94 coordinates
based on the analysis of week 0822-0900 sinex files.
1.0 Analysis Procedures:
(1) Each centers sinex solutions are de-constrained by adding back
in a rotational uncertainty.
(2) Covariance matrices are re-scaled by computing the chi**2/freedom of
the position residuals to the reference sites in IGS00 from an loosely
constrained solution that is rotated and translated on to the IGS00 system.
During the rotation/translation step, outliers (4-sigma based on fit) are
removed and this new scheme is more robust when some of the reference sites
have moved (due earthquakes and/or equipment changes).
(2o) This procedure was replaced Week 1203 with the one described above.
Covariance matrices from each center are re-scaled to generate
unit increment in chi square per degree in the tight constraints solution.
The values are are based in the chi**2 per degree of freedom increment
when the loosely constrained solution is constrained to the ITRF1996
coordinates of the 55 Reference sites. Orientation changes are estimated
in this step, but translations and scale are NOT estimated.
(3) The tight solution is generated with the following constraints on
the core sites. Starting Week 0858, ITRF94 is used for the coordinate
system. Starting Week 0878, we changed the site selection here to use
WTZR and GOL2. Starting Week 0897 we stopped using MADR as a core site.
We continue not use MADR in the reference site list.
Earth rotation parameters are estimated for each center (even when not given
in the original SINEX files. In this case the partial derivatives are
computed from the station coordinates).
(4) When the combined and center solutions are compared to ITRF97, the
heights are given a variance 10 times larger than the horizontal coordinates.
The same variance ratio is used when the RMS to ITRF97 core sites is
computed.
(5) Starting Week 0826, we show the differences in the coordinates for
five non-core sites, in remote areas. Four of these sites are processed
by all centers. These sites are not used in the RMS calculations or
the transformation estimation to the 13 core sites. The change in procedure
was because FORT is no longer being processed by all centers. AREQ has
been added to the list for this reason. After Week 0943, when the reference
site list increased we no long summarize additional sites.
(6) Starting Week 0826, we start to show a comparison of each centers
results with the combined solution for the week. When the constraints
are applied to loose combined solution to translate, rotate and scale it
to the ITRF97, the constraints are actually applied using the full
covariance matrix of the combined solution (rather than simply directly
applying the transformations to the coordinates). The approach we use
constrains the center of mass to have zero variance relative to ITRF97.
The result of this is that the combined solution has the same center
of mass position and scale as ITRF97, and therefore when each of the
centers are compared to the combined solution, they generate very similar
translations and scales as they do the ITRF97. Had we simply applied
the transformations to the coordinates, the translations and scale would
have been the difference between the combined translations and scale and
the individual center's translations and scale.
This new section is numbered 4.0.
(7) Starting Week 868, we updated the coordinates of sites not included
in the ITRF94 coordinate files. This introduces a discontinuity in the
the adjustments to some of the "isolated" sites shown below.
2.0 COMBINED FIT TO IGS05
Transformation of loose solution COMBINED to IGS05
-----------------------------------------------
For 0 Sites, RMS after 7 parameter transformation 0.0 mm COMBINED wrt IGS05
X-tran +- Y-tran +- Z-tran +- Scale +-
(mm) (mm) (mm) (mm) (mm) (mm) (ppb) (ppb)
0.0 10000.0 0.0 10000.0 0.0 10000.0 0.000 10.000 COMBINED CoM
RMS Fits of COMBINED to IGS05
Adjustments to core site positions for COMBINED
SITE dNorth +- dEast +- dUp +-
(mm) (mm) (mm) (mm) (mm) (mm)
Reference sites NOT used
3.0 CENTER FITS TO IGS05
4.0 CENTER FITS TO COMBINED SOLUTION
5.0 EOP ESIMATES FROM THE CONSTRAINED COMBINED SOLUTION
MJD Xpole Ypole UT1-UTC LOD Xsig Ysig UTsig LODsig Nr Nf Nt Xrt Yrt Xrtsig Yrtsig XYcorr XUTcor YUTcor
(10**-6") (0.1 usec) (10**-6") (0.1 usec) (10**-6"/d) (10**-6"/d)
******** 0 0 0 0 10062 10062 6708 1491 0 0 0 0 0 10050 10050 0.000 0.000 0.000
******** 0 0 0 0 14300 14300 6944 1633 0 0 0 0 0 10100 10100 0.000 0.000 0.000
******** 0 0 0 0 22622 22622 7535 1764 0 0 0 0 0 10149 10149 0.000 0.000 0.000
******** 0 0 0 0 32016 32016 8459 1886 0 0 0 0 0 10198 10198 0.000 0.000 0.000
******** 0 0 0 0 41788 41788 9667 2000 0 0 0 0 0 10247 10247 0.000 0.000 0.000
******** 0 0 0 0 51745 51745 11106 2108 0 0 0 0 0 10296 10296 0.000 0.000 0.000
******** 0 0 0 0 61812 61812 12732 2211 0 0 0 0 0 10344 10344 0.000 0.000 0.000
6.0 NO ANTENNA OFFSETS AVAILABLE
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