From AC Tue Mar 14 08:03:33 1995 From: AC (AC) Date: Tue, 14 Mar 1995 8:03:33 PST Subject: [IGSMAIL-0906] Wk 0782-785 IGS Final Orb. Message-ID: ****************************************************************************** IGS Electronic Mail Tue Mar 14 8:03:33 PST 1995 Message Number 0906 ****************************************************************************** Author: AC Coordinator Subject: Wk 0782-785 IGS Final Orb. ******************************************************************************* IGS Final orbits/clocks completed and put onto CDDIS (Weeks 782 - 785) (Jan. 01 - Jan. 28, 1995) ******************************************************************************* According to the recommendations of the Analysis Centre Workshop the IGS Rapid Orbits were recomputed using up to date orbits and the final EOP values of Bulletin B, published by IERS. ( Daily values, page 2 of Bull. B ) The EOP were corrected for the difference between the IERS pole series and ITRF as published in the IERS 1993 Annual Report (p. II-19, Table II-3), so both the IGS orbits and the associated ERP files are consistent with ITRF93 (current epoch). We have downloaded all the submitted ephemeris and ERP files from CDDIS before the final orbit/clock combination to ensure that the sets are complete and up to date. In the final combination we have largely followed the actions taken during the Rapid orbit generation and since there were very few orbit resubmissions, both the IGS Rapid and Final orbits are virtually the same except for the the orientation difference (the current Bull.A and the final Bull.B). Orbit evaluation are also nearly the same, since we used centre specific ERP in the long arc evaluations. For more information see the corresponding summary files on CDDIS. Starting with the GPS week 742 a new clock combination scheme was put in place for the final orbit/clock combinations. The clock solution alignment and centre clock weight assignment are based on non SA broadcast satellite corrections only (PRN12, 15, 20). This should result in more realistic and objective clock weighting than employed before, provided that the non SA satellites are representatives of centre clock solution quality. Starting with the GPS week 756 the new IGS erp format (see IGSMAIL# 662) is used by all Analysis Centres and for the IGS erp files. ERP rates, whenever given, are also utilized in both orbit combination and the long arc evaluation. PRODUCTS GENERATED: The resulting final IGS ephemeris and clocks are in daily files in the SP3 format. The sat. orb. accuracy codes displayed in the headers are based on weighted RMS for each satellite. Note that each file contains all the submitted satellites. If satellite or centre had to be excluded from the combination it is noted in the summary file along with the reason for doing so. The IGS FINAL ORBIT files generated and uploaded into CDDIS @ NASA/GSFC are: IGS07820-6.SP3 IGS GPS orbit/clock files for days 0-6, week 0782 IGS07830-6.SP3 IGS GPS orbit/clock files for days 0-6, week 0783 IGS07840-6.SP3 IGS GPS orbit/clock files for days 0-6, week 0784 IGS07850-6.SP3 IGS GPS orbit/clock files for days 0-6, week 0785 IGS07827.ERP EOP associated with the above orbits (Bull. B aligned to ITRF) IGS07837.ERP EOP associated with the above orbits (Bull. B aligned to ITRF) IGS07847.ERP EOP associated with the above orbits (Bull. B aligned to ITRF) IGS07857.ERP EOP associated with the above orbits (Bull. B aligned to ITRF) IGS07827.SUM Complete summary/statistics report IGS07837.SUM Complete summary/statistics report IGS07847.SUM Complete summary/statistics report IGS07857.SUM Complete summary/statistics report The old Rapid Orbit files have been renamed (on CDDIS) to: (Note this is temporary, based on discussions with AC and GB and may be changed ) IGR07820-6.SP3 Rapid service orbits/clocks for days 0-6, week 0782 IGR07830-6.SP3 Rapid service orbits/clocks for days 0-6, week 0783 IGR07840-6.SP3 Rapid service orbits/clocks for days 0-6, week 0784 IGR07850-6.SP3 Rapid service orbits/clocks for days 0-6, week 0785 IGR07827.ERP Rapid service EOP associated with the above orbits (Bull A) IGR07837.ERP Rapid service EOP associated with the above orbits (Bull A) IGR07847.ERP Rapid service EOP associated with the above orbits (Bull A) IGR07857.ERP Rapid service EOP associated with the above orbits (Bull A) IGR07827.SUM Rapid service complete summary/statistic report IGR07837.SUM Rapid service complete summary/statistic report IGR07847.SUM Rapid service complete summary/statistic report IGR07857.SUM Rapid service complete summary/statistic report ***************************************************************************** REMARKS/CORRECTIONS: 1. Starting on January 1, 1993 all the IGS products, including the IGS combined orbits, are based on ITRF93. This reference frame change introduces a small discontinuity, mainly in orientation. More specifically the following changes took effect on Jan 1/95 (day 0, GPS week 782): (IGS(ITRF93)-IGS(ITRF92); epoch 1995.0; transformation parameters consistent with the IERS conventions) IGS Orbits: T1(cm) T2(cm) T3(cm) D(ppb) R1(mas) R2(mas) R3(mas) -.9 -1.2 .3 0 1.66 .68 .4 rates -.02 -.11 .15 0 .12 .15 -.13 The corresponding erp file changes: (IGSERP(ITRF93)-IGSERP(ITRF92)): X(ITRF93)-X(ITRF92) = -0.68mas Y(ITRF93)-Y(ITRF92) = -1.66mas UT1(ITRF93)-UT1(ITRF92)= 0.034ms These parameters which are consistent with the IERS values, can be used to precisely relate the 1994 and 1995 IGS combined products. For more details please refer to IGSMAIL#824. 2. Starting with week 0782 the IERS Bulletin B pole used as reference is first corrected with the parameters published in the IERS 1993 Annual Report, page II-19 (Table II-3), which aligns the pole series with the ITRF93 [Mailed From: Jan Kouba ]