From: rothacher@ubeclu.unibe.ch (MARKUS ROTHACHER) Author: Markus Rothacher Date: 30 Oct 1998 18:07:59 Subject: [IGEXMail-0052] First Precise GLONASS Orbits from CODE Precedence: bulk ****************************************************************************** IGEX Electronic Mail 30-Oct-1998 18:07:59 Message No 0052 ****************************************************************************** Author: rothacher@ubeclu.unibe.ch (MARKUS ROTHACHER) Subject: First Precise GLONASS Orbits from CODE Author: Markus Rothacher Dear Colleagues, we would like to announce that the first GLONASS precise orbits have been computed at the CODE Analysis Center using the data of the global IGEX network. The analysis was done by fixing the GPS orbits and Earth rotation parameters to the CODE final GPS solution and estimating orbital parameters only for the GLONASS satellites using double differences (including double differences between GLONASS and GPS satellites). The orbits were computed for GPS week 0979 (the week before the official start of IGEX) and stem from overlapping 3-day solutions with 3-day arcs. The GLONASS/GPS precise orbits are available at the anonymous ftp area of CODE and can be downloaded for tests as follows: ftp 130.92.6.17 (-or- ubeclu.unibe.ch) userid: anonymous passwd: "your e-mail address" cd aiub$ftp cd code get corWWWWD.eph (WWWW: GPS Week, D: Day of GPS Week) bye The orbits are given in the SP3 format (modified for GLONASS according to IGEXMAIL #0039) and refer to the ITRF96 system. The satellite clock values included in the precise orbit files are broadcast clock values for GLONASS (no improvement done so far) and precise CODE estimates for GPS satellites. Although only a very few IGEX station were operational at this time, the orbits are of a quality of about 30 cm, a factor of 8 better than the GLONASS broadcast orbits. The quality has been assessed using two approaches: 3-Day Fit: An rms of about 20-30 cm is obtained when fitting a 3-day arc through the satellite positions contained in three consecutive SP3 files SLR O-C Check: We computed the O-C (observed-computed) values of the SLR data to the GLONASS satellites for this week. The corresponding rms is about 30-40 cm. The table below summarizes the SLR quality check of GLONASS orbits obtained from the broadcast messages and computed using the GLONASS microwave data: DOY RMS O-C RMS O-C Broadcast Microwave 284 1.71 0.37 285 2.44 0.39 286 1.78 0.38 287 1.85 0.43 288 1.55 0.49 289 1.38 0.26 From now on we will try to deliver precise GLONASS orbits on a weekly basis with a delay of about 2-3 weeks. Any feedback about the quality of the orbits (e.g. from regional GLONASS processing) would be very welcome. We would like to thank the operators of the IGEX sites and the SLR groups for their efforts. Markus Rothacher Tim Springer CODE Analysis Center -------------------------------------------------------------------------------- Dr. Markus Rothacher Phone : ++41-31-631-8591 Astronomical Institute Fax : ++41-31-631-3869 University of Berne E-mail : markus.rothacher@aiub.unibe.ch Sidlerstrasse 5 AFTP : ftp ubeclu.unibe.ch (130.92.6.17) CH-3012 Berne cd aiub$ftp after login Switzerland WWW : http://www.cx.unibe.ch/aiub/