[IGSMAIL-5970]: z-offset update for R23/R714 planned at the beginning of GPS week 1542

[Ralf Schmid]

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IGS Electronic Mail      15 Jul 06:16:03 PDT 2009      Message Number 5970
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Author: Florian Dilssner, Rolf Dach and Ralf Schmid


Dear IGS colleagues!

Recent analyses have shown that GLONASS-M satellite R23/R714 behaves 
completely differently than other satellites of the same type; see, 
e.g., the talks (German only!) of Dilssner F. et al. and Dach R. et al. at
http://tu-dresden.de/geo/gi/aws09

z-offset estimations with x- and y-offsets as well as phase center 
variations (PCVs) kept fixed to igs05.atx values yield differences of 
about 35 cm compared to the value contained in igs05.atx (227.72 cm). 
Thus, the GLONASS Analysis Centers of the IGS have decided to update 
this z-offset value with the mean value of CODE and ESOC test solutions 
of 191.68 cm (CODE and ESOC results agree at the 5 cm level using 
different time intervals and independent software packages). All other 
calibration values of R23/R714 (x- and y-offset, PCVs) are kept fixed 
for the time being, although the satellite also shows strong 
azimuth-dependent PCVs.

This updated offset value will be contained in igs05_1542.atx. All AC 
results starting with GPS week 1542 (26 July 2009) will be based on that 
new z-offset value. Sorry for any inconvenience this may cause!

Normally, atx values are not changed after publication unless they are 
designated "preliminary", but the R23/R714 error is simply too large to 
ignore. Other z-offset values of recently launched satellites designated 
"preliminary" will probably not be updated before the switch to ITRF2008 
and a new igs08.atx realization in the first half of 2010(?).

With best regards,

Florian Dilssner, Rolf Dach and Ralf Schmid
on behalf of the IGS Antenna Working Group