[IGS-DCWG-130] Re: Problematic GLONASS navigation files ...

[Nacho Romero]

Dear Oskar,

It is not correct to post to this list as it is only for members of the 
Data Center Working group, and only for data center questions and not 
for data questions!  please use the IGSMail email list for general 
questions as it also benefits the community at large.  Thanks.

The issue you note is indeed correct, a certain version of the RINEX 
generation software was generating glonass navigation files with a 1 sec 
epoch issue as you have found due to the introduction of a leap second 
during last summer.  It took some time to correct the problem at all the 
stations affected so it also affected the general "brdc" navigation file.

I would suggest that you simply filter the file before using it and you 
should be fine with a command of the sort;
 > grep -v "  1.0" brdc220.15g > brdc220.15g_clean

let me know privately if you can proceed with the '_clean' file

I will bring this issue up within the IGS data centers to see how we 
address it for the older stored brdc files.

regards,

Dr Nacho Romero
IGS Infrastructure Committee Chair



On 02/11/2015 07:53, Oskar Sterle wrote:
> Dear Mr., Ms.,
>
> I was doing some processing of GPS / GLONASS data on a basis of 
> broadcast  ephemeris and I got extremely bad results for GLONASS data. 
> After some analysis I found that the GLONASS navigation files are, in 
> my opinion, incorrect. I found out that the problem is evident after 
> leap second 17 introduction, where some of the broadcast navigation 
> data, stored in brdcDDD0.YYg files, contain an additional 1 second in 
> an epoch. As an example, in a file brdc2200.15g 
> (ftp://cddis.gsfc.nasa.gov/gnss/data/daily/2015/220/15g/brdc2200.15g.Z) there 
> is:
>
>  1 15  8  8  0 45  0.0-0.151447951794D-03 0.000000000000D+00 
> 0.180000000000D+04
>    -0.112675112305D+05-0.160253047943D+01 0.931322574616D-09 
> 0.000000000000D+00
> 0.256164208984D+04-0.266967201233D+01-0.931322574616D-09 
> 0.100000000000D+01
>    -0.227310625000D+05 0.494499206543D+00 0.186264514923D-08 
> 0.000000000000D+00
> ...
>  1 15  8  8  1 15  0.0-0.151447951794D-03 0.000000000000D+00 
> 0.360000000000D+04
>    -0.143798266602D+05-0.181855010986D+01 0.000000000000D+00 
> 0.000000000000D+00
> -0.187464013672D+04-0.222508335113D+01-0.186264514923D-08 
> 0.100000000000D+01
>    -0.209729423828D+05 0.144630336761D+01 0.186264514923D-08 
> 0.000000000000D+00
> ...
>  1 *15  8  8  1 15  1.0*-0.151447951794D-03 0.000000000000D+00 
> 0.360000000000D+04
>    -0.143798266602D+05-0.181855010986D+01 0.000000000000D+00 
> 0.000000000000D+00
> -0.187464013672D+04-0.222508335113D+01-0.186264514923D-08 
> 0.100000000000D+01
>    -0.209729423828D+05 0.144630336761D+01 0.186264514923D-08 
> 0.000000000000D+00
>
> It can be seen that the red epoch has an increment of 1 second. Is 
> this normal? Probably not, since any position of satellite R01 after 
> 1:15:01 is wrong for approximately 4km (1s of travel time).
>
> Did anybody else also encountered this problem?
>
> Oskar Sterle
> University of Ljubljana, Slovenia
>
>
> _______________________________________________
> IGS-DCWG mailing list
> IGS-DCWG at igscb.jpl.nasa.gov
> https://igscb.jpl.nasa.gov/mailman/listinfo/igs-dcwg

-- 
Best regards,
Nacho
_______________________________________________________________

Ignacio (Nacho) Romero
Aerospace Engineer, PhD
SAC @ ESA/ESOC/HSO-GN
IGS Infrastructure Committee
www.canaryadvancedsolutions.com
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