From Tim.Springer at esa.int Mon Nov 30 03:03:30 2009 From: Tim.Springer at esa.int (Tim.Springer at esa.int) Date: Mon, 30 Nov 2009 12:03:30 +0100 Subject: [IGSMAIL-6030]: GLONASS Broadcast Ephemerides (GLSV, KHAR) Message-ID: ****************************************************************************** IGS Electronic Mail 30 Nov 03:04:20 PST 2009 Message Number 6030 ****************************************************************************** Author: Tim Springer Dear Colleagues, As some of you may have noticed the broadcast orbits in the IGS GLONASS combination always look very bad for the Monday of each week. In doing some "reprocessing" for the upcoming AGU meeting I have run into a similar problem with our software as well with "crashing" Monday solutions. Whilst digging into this problem I found out that in the reprocessing I forgot to disable the usage of the combined "brdc" file which we normally ignore in our IGS routine operations since it gave some problems in the past and still does today. So I have taken some time to look into where the problem comes from. It seems that the root cause is that almost every Monday, probably due to the week "switch over", the GLONASS broadcast ephemerides from the stations GLSV and KHAR are producing erroneous epochs. This can easily be seen in the files as they report the epoch as, e.g., 44 min and 59.0 sec but all other stations give the same information for the 45 min and 00.0 sec epoch. Since the merged "brdc" file just adds these different epochs to the merged file also the combined "brdc" file contains this error. So to resolve this issues I propose the following corrective actions: Station managers from GLSV and KHAR are to correct their software for the generation of broadcast ephemerides The data centres generating combined GLONASS brdc files should ignore all information that is not given for the full minutes The ACs are advised to do the same as the data centres The IGS combination software should also follow this recommendation The Rinex navigation header of GLSV and KHAR indicates that the following software(s) were used: GLSV: teqc 2008Oct2, NovaRS 1.4.2.0 MAO22.05.2009 KHAR: teqc 2008Oct2, NovaRS 1.3.0.0 MAO22.05.2009, and also NovaRS 1.4.2.0 Since teqc 2008Oct2 is used at multiple sites for generating and/or checking the broadcast ephemerides it seems very unlikely that teqc is the cause. GLSV and KHAR are the only two sites listing the NovaRS software in their broadcast navigation files. So most likely the NovaRS software is causing the issue at hand. To give you an idea of the size of this effect below a Table from the IGS GLONASS combination where the broadcast is compared to the IGS combined product. The ">>>>>" fields for the RMS and the WRMS "nicely" show the size of this effect and this has been happening for a long time now for day 1 of the week. So please take the above corrective actions ASAP! Table 1.1557.c GPS week : 1557 MJD: 55143.0-55149.0 Daily transformation of broadcast orbits (brd) to the combined IGL orbit. Mean and standard deviations of the transformation parameters for the whole gpsweek. CEN WEEK DAY | DX DY DZ RX RY RZ SCL RMS WRMS | TOFT TDRFT | [mm] [mm] [mm] [uas] [uas] [uas] [ppb] [mm] [mm] | [ps] [ps/d] -------------+------------------------------------------------------------+---------------- brd 1557 0 | 112 -72 88 1274 2226 -11990 90.1 1610 1610 | 502456 0 brd 1557 1 |31360 -3751 -7813 -755 -230800 135800 71.4 >>>>> >>>>> | 499969 0 brd 1557 2 | -113 22 210 3234 -308 -10710 90.1 2029 2029 | 497725 0 brd 1557 3 | -154 -136 80 518 459 -16110 90.7 2095 2095 | 500480 0 brd 1557 4 | 109 -22 100 -2703 1587 -20130 89.1 1831 1831 | 505017 0 brd 1557 5 | 78 5 22 -371 1875 -21730 86.3 1988 1988 | 504185 0 brd 1557 6 | -64 34 57 -1400 1249 -20300 87.0 2004 2004 | 504162 0 -------------+------------------------------------------------------------+---------------- brd 1557 mean| 4475 -559 -1036 -29 -31958 4975 86.4 >>>>> >>>>> | 501999 0 brd 1557 sdev|11855 1408 2988 1928 87684 57844 6.8 >>>>> >>>>> | 2691 0 Kind regards, Tim --------------------- Tim Springer Navigation Support Office, OPS-GN (nng.esoc.esa.de) European Space Operations Centre Robert Bosch Strasse 5 64293 Darmstadt Germany Tel: +49-6151-90-2029 Fax: +49-6151-90-3129