From tah at mtglas2.mit.edu Mon Nov 10 11:57:17 2003 From: tah at mtglas2.mit.edu (Tom Herring) Date: Mon, 10 Nov 2003 14:57:17 -0500 (EST) Subject: [IGSREPORT-10758] Wk 2651 MIT T2 Analysis Report Message-ID: <200311101957.OAA14131@mtglas2.mit.edu> ****************************************************************************** IGS Electronic Report 10 Nov 11:57:32 PST 2003 Message Number 10758 ****************************************************************************** Author: Thomas Herring ******************************************************************************** MIT ANALYSIS REPORT GPS-WEEK 2651 Dates: 30oct27 to 30nov02 ******************************************************************************** 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 MIT2651g.SNX Combined sinex file from all available analysis centers MIT2651g.SUM Name of this summary file MIT2651g.RES File of the individual AC position estimates residuals to the combined solution for the week. 0.0 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. 0.0 Starting Week 1202 adopted IGS01P37_RS54 for reference frame. Dropped KOKB and FAIR from frame definition. 0.1 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. 0.2 Starting Week 1110, we stopped applied a pole-tide correction to SIO sinex files because this correction is already made in their analysis. 0.3 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. 0.4 Starting Week 1020, we adopted the ITRF97 reference frame 0.5 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 IGS00 Transformation of loose solution COMBINED to IGS00 ----------------------------------------------- For 0 Sites, RMS after 7 parameter transformation 0.0 mm COMBINED wrt IGS00 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 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 IGS00 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 10051 10051 6701 1350 0 0 0 0 0 2025 2025 0.000 0.000 0.000 ******** 0 0 0 0 10308 10308 6872 1366 0 0 0 0 0 2049 2049 0.000 0.000 0.000 ******** 0 0 0 0 10949 10949 7299 1382 0 0 0 0 0 2074 2074 0.000 0.000 0.000 ******** 0 0 0 0 11921 11921 7947 1398 0 0 0 0 0 2098 2098 0.000 0.000 0.000 ******** 0 0 0 0 13158 13158 8772 1414 0 0 0 0 0 2121 2121 0.000 0.000 0.000 ******** 0 0 0 0 14600 14600 9733 1430 0 0 0 0 0 2145 2145 0.000 0.000 0.000 ******** 0 0 0 0 16198 16198 10799 1445 0 0 0 0 0 2168 2168 0.000 0.000 0.000