[IGSMAIL-6107]: ESA/ESOC Ultra-Rapid and Rapid GNSS Solutions

[Tim.Springer at esa.int]

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IGS Electronic Mail      17 Mar 09:29:14 PDT 2010      Message Number 6107
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Author: Tim Springer


Dear IGS Colleagues,

With this e-mail we are proud to announce an other important enhancement 
in our ESA set of IGS products. Starting with GPS week 1574 day 1 our 
Rapid and our Ultra-Rapid (from hour 12) products are now true GNSS 
products containing the positions and clock offsets for all "well behaved" 
GPS and GLONASS satellites. This enhancement has been made possible thanks 
to the speed improvements that were made in the latest version of our 
NAPEOS software. As our products are now based on a truly combined GNSS 
analysis our orbit and clock products allow for very accurate GNSS precise 
point positioning simultaneously using GPS and GLONASS observations. 
Especially for kinematic solutions the usage of both systems is of great 
benefit thanks to the significant increase in the number of satellites 
from ~30 to ~50.

GLONASS clocks.
One important thing to notice is a significant difference between our 
Final and Ultra-Rapid/Rapid GLONASS clocks. When processing both code and 
phase observations from the GLONASS system one has to estimate what we 
call an "intersystem bias" for each receiver-Glonass_satellite pair. This 
is caused by the fact that internally in the current generation of GNSS 
receivers/antennas the different frequencies of the GLONASS satellites 
cause different delays in the order of tens of nanoseconds. The estimation 
of these biases significantly increases the size of the main matrix and 
thus increases the CPU time. For our Ultra-Rapid/Rapid solutions we have 
therefore decided to use the GLONASS code measurements only in 
preprocessing. This mean that in the main parameters estimation we do not 
use the code observations and consequently we do not have to estimate the 
intersystem biases as those are only observable by the code measurements. 
In this way the estimated GLONASS clocks in our Ultra-Rapid/Rapid remain 
aligned (more or less) to the GLONASS time system whereas the GLONASS 
clocks from our final solution are aligned to the GPS time system. The 
difference between the two time systems is around 330-350 ns. So when 
comparing our Rapid and Final GLONASS clocks you will see this difference. 
However, after removal of this bias the difference between the satellite 
clocks is at the level of 0.04 ns. When using the clocks, e.g. for PPP, 
you will not notice this difference in the values of the intersystem 
biases you (have to) estimate. Or you, alternatively, you could ignore the 
GLONASS code observations like we do in our Ultra-Rapid/Rapid solutions.

For those people who want to use our GNSS products you will find them on 
our anonymous ftp:
ftp://dgn6.esoc.esa.int/products

We hope the GNSS community can make good use of these products! And if you 
have any comments and or questions please do not hesitate to contact us!

If you use our products please make sure to properly acknowledge our 
efforts (see, e.g., ftp://dgn6.esoc.esa.int/products/000readme.esoc). 

Many greetings,
The ESOC IGS Team.


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Tim Springer
Navigation Support Office, OPS-GN (nng.esoc.esa.de)
European Space Operations Centre
Robert Bosch Strasse 5
64293 Darmstadt
Germany
Tel: +49-6151-90-2029  Fax: +49-6151-90-3129