[IGSMAIL-3087]: New IGS Clock Combination

[tim.springer at aiub.unibe.ch]

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IGS Electronic Mail      03 Nov 07:00:38 PST 2000      Message Number 3087
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Author: Tim Springer


Dear IGS colleagues,

As agreed upon during the last IGS Analysis Center workshop, held from
25-29 September at the U.S. Naval Observatory, the new IGS clock combination
will become official starting with the products of GPS week 1087, day 0
(November 5, 2000).

This means that coming Monday the clock products in the IGS rapid orbit
combination will be based on the new clock combination scheme.
The new "clock-RINEX" format is used for the exchange of estimates
and for the distribution of results.  The new clock combination adds
considerable robustness and outlier detection, which requires far less manual
intervention, as well as the new receiver clock products. 
This new clock combination has been running in a demonstration mode since the 
beginning of this year for both the final and rapid orbits. The results were
used for the navigation solutions and the results were published in the regular 
Final and Rapid combination reports. Separate clock combination results,
a summary file and a clock-RINEX file, were made available on anonymous fop
in Berne. 

In principle this new clock combination does not change anything for the
user of IGS products. The results from the new clock combination will be
included in the IGS orbit (SP3) products to guarantee normal usage.
Two new files will result from this new combination. 
  1) The resulting combined clock estimates for satellite and station clocks.
     This file will be called igrWWWWD.clk
  2) A summary file giving details of the clock combination.
     This file will be called igrWWWWD.cls 

Of course the most important statistics of the clock combination will be 
included in the normal summary in the "old" way. These are the offset, drift 
(wrt. broadcast), and rms of the clock estimates (wrt. combined clocks).

These new files will be made available in the normal directories at the
differente IGS data centers and the IGSCB where you also find the other 
products.

The new combination offers enhanced capabilities because the clock-RINEX
file will contain clock estimates sampled at 5min compared to 15min in the
orbit (SP3) files. This should especially help to further improve the 
precise point positioning (ppp) results. Furthermore, the new product 
contains the receiver clock estimates which will give additional feedback
to the station managers. 

If you have any further questions regarding this or any of the other IGS
products please do not hesitate to contact me.

Kind regards,
         Tim Springer
         IGS Analysis Center Coordinator


ps. A description of the clock-RINEX format is available at the IGSCB and
    at the USNO.
    ftp://igscb.jpl.nasa.gov/igscb/data/format/rinex_clock.txt
    http://maia.usno.navy.mil/gpst/clock-format

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 Tim Springer                      Astronomical Institute, University of Berne 
 springer at aiub.unibe.ch            Sidlerstrasse 5, CH-3012 Bern, Switzerland  
 http://www.aiub.unibe.ch/         Tel: +41 31 6318592    Fax: +41 31 6313869
 ftp://ftp.unibe.ch/aiub
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