From tah at chandler.mit.edu Wed Jul 2 23:14:18 2003 From: tah at chandler.mit.edu (Tom Herring) Date: Thu, 3 Jul 2003 02:14:18 -0400 (EDT) Subject: [IGSREPORT-10387] Wk 1223 MIT T2 Analysis Report Message-ID: <200307030614.CAA25131@mtglas.mit.edu> ****************************************************************************** IGS Electronic Report 02 Jul 23:15:10 PDT 2003 Message Number 10387 ****************************************************************************** Author: Thomas Herring ******************************************************************************** MIT ANALYSIS REPORT GPS-WEEK 1223 Dates: 03jun15 to 03jun21 ******************************************************************************** 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 MIT1223g.SNX Combined sinex file from all available analysis centers MIT1223g.SUM Name of this summary file MIT1223g.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