From AC Fri Aug 20 04:17:56 1999 From: AC (AC) Date: Fri, 20 Aug 1999 4:17:56 PDT Subject: [IGSMAIL-2432] ITRF96/97 IGS product changes Message-ID: ****************************************************************************** IGS Electronic Mail Fri Aug 20 4:17:56 PDT 1999 Message Number 2432 ****************************************************************************** Author: AC Coordinator Subject: ITRF96/97 IGS product changes Dear IGS colleagues, On 1 August 1999 the IGS changed its realization of the International Terrestrial Reference Frame by switching from the ITRF96 to the ITRF97. At the same time the set of reference stations (RF) was slightly enhanced from 47 to 51 sites. The main change was the inclusion of a few sites for which the accuracy was insufficient in the ITRF96 but which now seem to be well determined in the ITRF97. A SINEX file containing the necessary information about these 51 reference stations may be found at the IGS Central Bureau (ftp://igscb.jpl.nasa.gov/igscb/station/coord/ITRF97_IGS_RS51.SNX). Although the ITRF96 and ITRF97 frames are nominally aligned globally in all 7 Helmert components and their rates, comparison of the IGS subset of RF sites shows significant differences between the ITRF96 and ITRF97 realizations. Several analysis centers have also observed these differences. Some detective work by Zuheir Altamimi and Remi Ferland has shown that this may be related to the use of the full covariance matrices to align the two ITRF solutions. Based on the differences observed by several of the analysis centers the expected differences between the IGS products based on the ITRF96 and ITRF97 reference frames are given below. These values are based on the work done by Remi Ferland at NRCan using the ITRF coordinates and velocities of 45 IGS reference stations. Transformation from IGS(ITRF96) to IGS(ITRF97) at epoch 01-AUG-1999: ==================================================================== TX TY TZ RX RY RZ D mm mm mm mas mas mas ppb Offset 0.3 0.5 -14.7 0.159 -0.263 -0.060 1.430 +/- 2.1 2.1 2.1 .090 .098 .088 .31 -------------------------------------------------------------------- dTX dTY dTZ dRX dRY dRZ dD mm/y mm/y mm/y mas/y mas/y mas/y ppb/y Drift -0.7 0.1 -1.9 0.013 -0.015 0.003 0.192 +/- .3 .3 .3 .011 .012 .011 .043 -------------------------------------------------------------------- * The IERS convention for the transformation parameters was followed. * The equivalent changes in polar motion, in the sense (ITRF97 - ITRF96), may be obtained using PMx = RY and PMy = RX. Unlike past IGS ITRF changes, the transformations should be quite exact, rotations in particular, for the IGS Final orbits/ERPs. This is the result of the minimum constraint solutions adopted for all AC and IGS final products at the end of 1998. For completeness the results of different analysis centers have been included below. The agreement with the expected changes is very good in most cases. I would like to thank all individuals who have taken the time and effort to study these differences and to report them, special thanks are due to Zuheir Altamimi and Remi Ferland who have done most of the hard work related to the ITRF97. Many thanks also to Jim Ray and Jan Kouba for their corrections and useful suggestions. Hoping to have informed you sufficiently I remain, with kind regards, Tim Springer IGS Analysis Center Coordinator Solution description -------------------- O1 : USNO: Rapid orbit differences for 20-26 July 1999 O2 : EMR: EMR10217.SUM final orbit product differences for GPS week 1021 C1 : EMR: Remi Ferland NRC SINEX vs ITRF97_GPS.SNX (RF47) C2 : IGN: Zuheir Altamimi ITRF96 vs ITRF97 using diagonal matrix (not full) C3 : EMR: EMR10217.SUM and EMR10227.SUM final coordinate product differences for GPS weeks 1021 and 1022 P1a: EMR: Remi Ferland PM differences (Oct/98-May/99) P1b: EMR: Remi Ferland PM differences based on MIT GNAAC (Oct/98-May/99) P2 : USNO: Marshall Eubanks based on VLBI (1979.6-1999.3). P3 : EMR: EMR10217.SUM final pole product differences for GPS week 1021 P4 : CODE: ERP differences 200/1993-212/1999 (IGSMAIL #2422) Transformations from ITRF96 to ITRF97 at epochs noted: -------------------------------------------------------------------------- TX(mm) TY(mm) TZ(mm) RX(mas) RY(mas) RZ(mas) D(ppb) EPOCH -------------------------------------------------------------------------- O1 1.1 0.0 8.4 0.07 -0.22 0.02 0.0 23-07-1999 O2 -0.9 1.0 -8.5 0.12 -0.22 -0.01 0.0 01-08-1999 -------------------------------------------------------------------------- C1a 1.2 0.0 -11.0 0.11 -0.21 -0.05 0.82 01-01-1997 C1b -0.0 -0.2 -16.4 0.08 -0.25 -0.11 1.25 01-01-1999 C2 0.8 0.6 -10.2 0.12 -0.15 -0.06 0.79 01-01-1997 C3 0.6 0.0 -12.0 0.12 -0.23 -0.01 1.33 01-08-1999 -------------------------------------------------------------------------- C1 -0.6 -0.1 -2.7 -0.011 -0.024 -0.028 +0.212 ** RATE ** C2 -0.3 -0.2 -1.4 -0.010 0.005 0.000 +0.22 ** RATE ** -------------------------------------------------------------------------- Earth rotation parameter difference (ITRF97 - ITRF96) at epochs noted: -------------------------------------------------------------------------- PMx(mas) PMy(mas) UT(ms) EPOCH -------------------------------------------------------------------------- P1a -0.27 0.17 01-01-1999 P1b -0.28 0.18 01-01-1999 P2 -0.18 0.19 0.013 01-01-1997 P3 -0.23 0.13 01-08-1999 P4 -0.23 0.07 19-07-1993 -------------------------------------------------------------------------- P2 0.004 -0.014 0.003 ** RATE ** P4 0.014 0.011 ** RATE ** -------------------------------------------------------------------------- -- ----------------------------------------------------------------------------- Tim Springer Astronomical Institute, University of Berne springer at aiub.unibe.ch Sidlerstrasse 5, CH-3012 Bern, Switzerland http://www.cx.unibe.ch/aiub/ Tel: +41 31 6318592 Fax: +41 31 6313869 http://ftp.unibe.ch/aiub ----------------------------------------------------------------------------- [Mailed From: Tim Springer ]