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[IGEXMail-0045] Remarks on IGEX Data Processing
- Subject: [IGEXMail-0045] Remarks on IGEX Data Processing
- From: rothacher @ ubeclu.unibe.ch (MARKUS ROTHACHER)
- Date: 28 Oct 1998 18:54:04
- Author: Markus Rothacher, Werner Gurtner
Precedence: bulk
******************************************************************************
IGEX Electronic Mail 28-Oct-1998 18:54:04 Message No 0045
******************************************************************************
Author: rothacher @ ubeclu.unibe.ch (MARKUS ROTHACHER)
Subject: Remarks on IGEX Data Processing
Author: Markus Rothacher, Werner Gurtner
Dear Colleagues,
During the first analyses of IGEX data we detected a few things that might
be of interest to IGEX participants:
(1) In our pseudorange processing in the single station mode we determine
station position: once per session
receiver clock offsets: once per epoch
GLONASS-GPS time offset: once per session
using the broadcast satellite orbits and clocks.
The results for the GLONASS-GPS time offsets typically look like this:
***************************************************************
GLONASS/GPS TIME OFFSETS: DAY 298, 1998
***************************************************************
FILE STATION NAME RCV TIME OFFSET (NS) RMS ERROR (NS)
---------------------------------------------------------------
1 BORG 12205M004 R100 1036.915 0.796
2 CSIR 30310M001 R100 1045.006 0.860
3 DLFT 13502M006 GG24 90.755 0.736
4 DLRA 14208M002 R100 1038.114 0.809
5 GODZ Z18 88.031 0.809
6 IRKZ Z18 85.250 0.758
7 KHAB Z18 84.824 0.777
8 KR0G 10422M001 Z18 69.476 0.714
9 LINR R100 1049.974 0.831
10 MDVZ Z18 84.844 0.739
11 METZ 10503M005 Z18 84.485 0.719
12 REYZ 10202M003 Z18 98.258 0.733
13 WTZG 14201M012 R101 -713.787 0.873
14 ZIMZ 14001M005 Z18 85.734 0.755
---------------------------------------------------------------
Although there are still systematic biases in these results (broadcast
orbit errors, satellite clock errors, ionospheric delays, ...) of the
order of a few 10 ns, we clearly see, that the R100 receivers show
differences between GLONASS and GPS time, which are about 1 microsecond
larger than those of the Ashtech receivers.
Currently the correction of UTC(SU) to UTC are of the order of 180 ns
according to a recent Bulletin T. The broadcast corrections from GLONASS
system time to UTC(SU) are of the order of -350 ns giving roughly
a system time difference GLONASS-GPS of +170 ns (the corrections of GPS
system time to UTC are of a few ns only).
The ADDITIONAL offsets estimated with several Asthech Z18 are between
zero and say +100 ns whereas the offsets estimated with R100 instruments
are about 1 microsecond larger (around 1100 ns).
This seem to indicate that there is a "GLONASS receiver clock" running
in the R100 which constantly differs from the GPS one by 1 microsecond.
-------------
Another hint that this may be the case is the remark in the Bulletin T:
"Daily values of C1 are given in the following table. They are obtained
as follows: the GLONASS data taken at the NMi Van Swinden Laboratorium,
Delft, The Netherlands, for highest elevation, are smoothed to obtain
daily values of [UTC(VSL)-GLONASS time] at 0h UTC; daily values of C1
are then derived from them using linear interpolation of [UTC-UTC(VSL)]
--> A time correction of + 1285 ns is also applied in order to ensure
continuity of C1 estimates on 1997, January 1 (MJD = 50449). The global
uncertainty of daily C1 values is of order several hundreds of
nanoseconds."
Van Swinden Laboratory is also using a R100 receiver, and they apply
this correction to smoothly continue the values determined by another
institution (was it Leeds University? Receiver type?) before January
1st, 1997.
The offset of approximately -700 ns seen at Wettzell might stem from the
fact that an older receiver (R-101) is used at this location.
(2) The Z18 receiver (at least the one running in Zimmerwald) generates
phase observations the absolute values of which obviously increase
with time. About two weeks after system start the values don't fit
anymore into the RINEX format field width F14.3. Please check if your
converter used to generate the RINEX observation files correctly
re-adjusts the phase values and does not merely increase the format width.
(3) There are still site logs missing for several IGEX sites. It would
help us a lot if these site logs could be made available soon.
We also noted that the information (MARKER NAME, ...) given in some
of the RINEX files are not correct. Please check the header information
in your RINEX files (it should be consistent with the site log
information, too).
Markus Rothacher & Werner Gurtner
CODE Analysis Center
--------------------------------------------------------------------------------
Dr. Markus Rothacher Phone : ++41-31-631-8591
Astronomical Institute Fax : ++41-31-631-3869
University of Berne E-mail : markus.rothacher @ aiub.unibe.ch
Sidlerstrasse 5 AFTP : ftp ubeclu.unibe.ch (130.92.6.18)
CH-3012 Berne cd aiub$ftp after login
Switzerland WWW : http://www.cx.unibe.ch/aiub/