From nacho at canaryadvancedsolutions.com Sat Apr 12 06:22:05 2014 From: nacho at canaryadvancedsolutions.com (Nacho Romero) Date: Sat, 12 Apr 2014 14:22:05 +0100 Subject: [IGSMAIL-6897] GLONASS Navigation message failure impact on IGS Message-ID: <53493DFD.9060106@canaryadvancedsolutions.com> Author: Nacho Romero, Infrastructure Committee Chairman Last April 1st, 2014 (d091) the GLONASS (GLO) constellation suffered an event as the uploaded navigation messages had an incorrect applicability times, this has been reported in the trade press as you are well aware (http://www.insidegnss.com/node/3979, http://gpsworld.com/glonass-gone-then-back/, http://gpsworld.com/altus-positioning-systems-pinpoints-cause-for-glonass-default/) the constellation continued emmitting navigation signals but the navigation message was incorrect, so some navigation users were affected if the incorrect navigation messages were not ignored, this lasted until well into April 2nd (d092). I have taken the IGS data from the Data Centers (DCs) in Rinex 2 and Rinex 3 to analyze what the impact of the GLO problems has been on the IGS; on the data holdings, on the GLO constellation coverage, and on the IGS products. This is a thorough but not complete or conclusive look into this issue, but after more than a week since the event I wanted to report to the IGS community about it with some hard facts. If interested please contact me and we can plan a more detailed study if needed. -- SUMMARY -- The conclusion is that the IGS was not affected; we have good amounts of GLO data over the period in the DCs and good GLO products. We continue to have enough data coverage for GLO, and regular product generation were not at all affected. Either the receivers ignored the incorrect navigation messages or were unaffected due to internal RAIMS checks. Thus the IGS network is stable due to its heterogeneity, as we have always advocated. This diversity of equipment in the network continues to ensure that we have a resilient IGS. This does not mean we did not have problems ... GLO coverage did suffer slightly (0-12 % per satellite on day 092; April 2nd) as can be seen from the Analysis Center processing reports for the Finals of last week, but we have so many stations providing data that it did not affect the GLO product generation. From those same Analysis reports it is clear that the availability of GPS observations was not affected. -- ANALYSIS -- In any case it is still of interest to understand the impact over certain stations since some show some small effect. I have projected below the expected tracking down to 3 deg elevation of GLO satellite data from each MGEX station (using MGEX to ensure many IGS Glonass tracking stations), and then compared to the actual observations contained in the downloaded data files. The figures below report the percent of the 24 hr GLO constellation orbits covered, so ... for the entire GLO constellation over 24 hr what should a station see in theory down to 3 deg, versus what it actually observes! Many stations can track down to 0 deg so they have more observations than theorized to 3 deg but that is not significant in this analysis. Almost all stations performed fine over the event (d091-092), for example: GLO coverage Observed||Theoretical 14091.MGEX/NetworkQC_R.txt:For R; kour : 34.03 % 33.94 % 14092.MGEX/NetworkQC_R.txt:For R; kour : 32.73 % 34.16 % 14093.MGEX/NetworkQC_R.txt:For R; kour : 34.94 % 35.20 % 14094.MGEX/NetworkQC_R.txt:For R; kour : 32.73 % 34.46 % 14090.MGEX/NetworkQC_R.txt:For R; ous2 : 35.89 % 35.29 % 14091.MGEX/NetworkQC_R.txt:For R; ous2 : 35.98 % 35.81 % 14092.MGEX/NetworkQC_R.txt:For R; ous2 : 36.07 % 36.02 % 14093.MGEX/NetworkQC_R.txt:For R; ous2 : 35.81 % 35.98 % 14094.MGEX/NetworkQC_R.txt:For R; ous2 : 36.15 % 35.85 % 14090.MGEX/NetworkQC_R.txt:For R; brst : 35.59 % 36.76 % 14091.MGEX/NetworkQC_R.txt:For R; brst : 36.24 % 37.07 % 14092.MGEX/NetworkQC_R.txt:For R; brst : 35.37 % 36.76 % 14093.MGEX/NetworkQC_R.txt:For R; brst : 35.63 % 36.98 % 14094.MGEX/NetworkQC_R.txt:For R; brst : 34.98 % 36.37 % 14090.MGEX/NetworkQC_R.txt:For R; usn5 : 32.25 % 34.24 % 14091.MGEX/NetworkQC_R.txt:For R; usn5 : 31.60 % 33.90 % 14092.MGEX/NetworkQC_R.txt:For R; usn5 : 31.12 % 34.20 % 14093.MGEX/NetworkQC_R.txt:For R; usn5 : 31.03 % 33.46 % 14094.MGEX/NetworkQC_R.txt:For R; usn5 : 31.25 % 33.59 % Some stations lost a few percent of GLO data on d091/092, but after those days they recovered fine, for example: GLO coverage Observed||Theoretical 14090.MGEX/NetworkQC_R.txt:For R; scrz : 31.29 % 33.07 % 14091.MGEX/NetworkQC_R.txt:For R; scrz : 28.65 % 32.55 % 14092.MGEX/NetworkQC_R.txt:For R; scrz : 28.26 % 33.07 % 14093.MGEX/NetworkQC_R.txt:For R; scrz : 31.77 % 33.25 % 14094.MGEX/NetworkQC_R.txt:For R; scrz : 30.34 % 32.99 % 14090.MGEX/NetworkQC_R.txt:For R; hofn : 39.37 % 38.37 % 14091.MGEX/NetworkQC_R.txt:For R; hofn : 36.20 % 38.85 % 14092.MGEX/NetworkQC_R.txt:For R; hofn : 33.03 % 38.41 % 14093.MGEX/NetworkQC_R.txt:For R; hofn : 38.85 % 38.28 % 14094.MGEX/NetworkQC_R.txt:For R; hofn : 37.93 % 38.11 % 14090.MGEX/NetworkQC_R.txt:For R; thtg : 31.34 % 32.77 % 14091.MGEX/NetworkQC_R.txt:For R; thtg : 28.47 % 32.73 % 14092.MGEX/NetworkQC_R.txt:For R; thtg : 29.08 % 33.59 % 14093.MGEX/NetworkQC_R.txt:For R; thtg : 32.25 % 33.38 % 14094.MGEX/NetworkQC_R.txt:For R; thtg : 30.56 % 33.20 % No effect in the GPS tracking of the MGEX stations is detected even when the GLO tracking is reduced a few percent over the 24 hr period, so this is a very minor effect on the days of the event of very limited consequence taking everything into consideration. some stations over the affected days submitted partial Rinex files (zim2, pado, etc) but its unclear if the partial files are due to the GLO problem or not, so I have not considered that issue, since in any case all the files a day after the event are fine again. Thanks. -- Best regards, Nacho _______________________________________________________________ Ignacio (Nacho) Romero Aerospace Engineer, PhD SAC @ ESA/ESOC/HSO-GN IGS Infrastructure Committee www.canaryadvancedsolutions.com _______________________________________________________________ Este mensaje, y en su caso, cualquier fichero anexo al mismo, puede contener informacion clasificada por su emisor como confidencial en el marco de su Sistema de Gestion de Seguridad de la Informacion siendo para uso exclusivo del destinatario, quedando prohibida su divulgacion copia o distribucion a terceros sin la autorizacion expresa del remitente. Si Vd. ha recibido este mensaje erroneamente, se ruega lo notifique al remitente y proceda a su borrado. 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