[IGSMAIL-6739] Re: Two Active GLONASS Slot 8 Satellites Temporarily -- Potential Difficulties

[Richard B. Langley]

Correction:
"The net result was that RINEX observation files from certain stations  
had a mixture of GLONASS 743 and 801K data ..."
-->
"The net result was that RINEX observation files from certain stations  
had a mixture of GLONASS 743 and 701K data ..."
(thanks to Tracy Cozzens)

Quoting "Richard B. Langley" <lang at UNB.CA>:

> Author: Richard Langley
>
> On day 53 (22 February) around 09:15 GPS Time, GLONASS 743 began  
> transmitting on frequency channel 6 using almanac slot 8 (R08). It  
> should replace GLONASS 701K (801) transmitting on frequency channel  
> -5, previously using almanac slot 8. However, GLONASS 701K was not  
> immediately switched off and/or did not switch slot numbers and  
> continued to transmit on frequency channel -5 for several days,  
> continuously identifying itself as a slot 8 satellite. While most  
> receivers were just tracking GLONASS 743, some tracked both GLONASS  
> 743 and 701K. While 701K was not in the broadcast almanac, it was  
> transmitting ephemeris records identifying itself as a satellite in  
> slot 8. The net result was that RINEX observation files from certain  
> stations had a mixture of GLONASS 743 and 801K data, with no  
> indication of which satellite was which. Of course, one could use  
> expected Doppler shift and/or code/carrier rate of change to figure  
> out which data records correspond to which satellite.
>
> Furthermore, the GLONASS navigation files from certain stations  
> contained a mixture of ephemeris records from GLONASS 743 and 701K.  
> For day 54, for example, GLONASS navigation files for 146 (non-MGEX)  
> stations were available at CDDIS. A number of these did not contain  
> any R08 entries, presumably because the corresponding receivers were  
> set to not track unhealthy satellites. Some of the files contained  
> R08 ephemeris records from earlier dates. These were ignored. This  
> left 82 files containing either GLONASS 701K and/or 743 ephemeris  
> records for day 54. These files were parsed to determine, for each  
> file, for which times ephemeris records were available for which  
> satellites. The results are summarized in the following plot:
> http://gge.unb.ca/Resources/glonass_slot8_in_nav_files_054_2013.pdf
>
> The station numbers correspond to those in the following table:
> http://gge.unb.ca/Resources/index_glonass_names.txt
>
> The navigation files from 29 stations contain both GLONASS 701K and  
> 743 records. It seems that it was Javad GNSS and Topcon receivers  
> that were primarily affected.
>
> Note that the CDDIS brdc***0.13g files on affected days have a  
> mixture of GLONASS 743 and 701K ephemeris records, but at any one  
> epoch, only one satellite is represented.
>
> Files from days 53 through 56 are affected.
>
> It appears that GLONASS 701K stopped identifying itself as a slot 8  
> satellite after about 15:15 GPS Time on day 56 and was not  
> subsequently tracked by any station supplying data files to CDDIS.
>
> See also IGSMail-6734, "Irregular GLONASS constellation change (for R08)."
>
> -----------------------------------------------------------------------------
> | Richard B. Langley                            E-mail: lang at unb.ca         |
> | Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/ |
> | Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142   |
> | University of New Brunswick                   Fax:      +1 506 453-4943   |
> | Fredericton, N.B., Canada  E3B 5A3                                        |
> |        Fredericton?  Where's that?  See: http://www.fredericton.ca/       |
> -----------------------------------------------------------------------------
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| Richard B. Langley                            E-mail: lang at unb.ca         |
| Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/ |
| Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142   |
| University of New Brunswick                   Fax:      +1 506 453-4943   |
| Fredericton, N.B., Canada  E3B 5A3                                        |
|        Fredericton?  Where's that?  See: http://www.fredericton.ca/       |
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