[IGSMAIL-6753] igs08_1734.atx: Update without "spikes" in GLONASS calibrations

[Robert Khachikyan]

Dear IGS colleagues!

The absolute IGS antenna correction file (igs08_wwww.atx) has been 
updated. The new release is called 'igs08_1734.atx'. The phase center 
variations (PCVs) for the GLONASS frequencies of the following 46 
antenna types were resubmitted by Geo++ GmbH:

ASH700936C_M    NONE
ASH700936D_M    SNOW
ASH700936E      NONE
JAV_GRANT-G3T   NONE
JAV_RINGANT_G3T NONE
JAVRINGANT_DM   NONE
JAVRINGANT_DM   JVDM
LEIAR10         NONE
LEIAR25         NONE
LEIAR25         LEIT
LEIAR25.R3      NONE
LEIAR25.R4      NONE
LEIAR25.R4      LEIT
LEIAR25.R4      SCIT
LEIAS05         NONE
LEIAS10         NONE
LEIAT504GG      NONE
LEIATX1230+GNSS NONE
LEIAX1202GG     NONE
LEIAX1203+GNSS  NONE
LEIGG02PLUS     NONE
LEIGS08         NONE
LEIGS09         NONE
LEIGS12         NONE
LEIMNA950GG     NONE
NAX3G+C         NONE
NOV702GG        NONE
NOV750.R4       NONE
RNG80971.00     NONE
SEPCHOKE_MC     NONE
SEPCHOKE_MC     SPKE
STXS9SA7224V3.0 NONE
TPSCR.G3        NONE
TPSCR.G3        SCIS
TPSCR3_GGD      CONE
TPSPG_A1+GP     NONE
TRM39105.00     NONE
TRM55971.00     NONE
TRM57970.00     NONE
TRM57971.00     NONE
TRM59800.00     NONE
TRM59800.00     SCIT
TRM59800.80     NONE
TRM59800.80     SCIT
TRMR8_GNSS      NONE
TRMR8_GNSS3     NONE

 From those phase center corrections erroneous spikes contained in the 
GLONASS PCVs were removed that were caused by a software bug in the 
format conversion from the Geo++ to the ANTEX format that was detected 
and corrected in November 2011. GLONASS PCVs in the ANTEX format 
provided by Geo++ prior to that date may be affected by spikes. Those 
GLONASS spikes are generally small, but could amount to several mm. As 
regards the antenna types contained in igs08.atx, the spikes were always 
smaller than 3 mm.

Among the 46 affected antenna types are 37 "original" phase center 
calibrations as well as 9 copied sets of corrections. The 37 original 
calibrations contained 281 spikes altogether. However, only 22 of them 
exceeded the 1 mm level:

3.0 mm <= spike              0
2.0 mm <= spike < 3.0 mm     8
1.0 mm <= spike < 2.0 mm    14
0.5 mm <= spike < 1.0 mm    38
0.2 mm <= spike < 0.5 mm    53
0.0 mm <  spike < 0.2 mm   168

More information can be found at the Geo++ website:
http://www.geopp.de/index.php?sprachauswahl=en&bereich=2&kategorie=3&artikel=221 

An online tool allows to visualize and check the GLONASS PCVs contained 
in ANTEX files for the existence of spikes. Details are given on the 
website.

The updated antenna correction model is available at
ftp://igs.org/pub/station/general/igs08_1734.atx
or
ftp://igs.org/pub/station/general/igs08.atx

As the magnitude of the spikes is small and as the induced PCV errors 
are isolated, the correction of the spikes should not have a systematic 
impact on IGS products based on GLONASS PCVs. Nonetheless, we apologize 
for any inconvenience this update may cause!

With best regards,
Ralf Schmid, Martin Schmitz and Robert Khachikyan
on behalf of the IGS Antenna Working Group