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Date: Fri, 03 Nov 2000 16:54:41 +0100 (MET)
From: tim.springer@aiub.unibe.ch
Subject: [IGSMAIL-3089]: IGS Ultra rapid products
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IGS Electronic Mail      03 Nov 09:10:01 PST 2000      Message Number 3089
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Author: Tim Springer


Dear IGS colleagues,

Starting next Monday the IGS Ultra rapid products (IGU's) will become official
IGS products. The IGU products have been generated in an experimental modus
since GPS week 1052. These products now have matured enough to make them 
official IGS products. The IGU products are an orbit file (sp3), an Earth 
Rotation file (IGS/IERS format), and a combination summary file.
The IGU products are based on the hourly RINEX files from the IGS network.
I would hereby like to take the chance to thank all station operators for
their great efforts in providing very reliable and high quality data on
an hourly basis.

The IGU products will contain 48 hours worth of orbits. The first 24 hours
contain a "real" orbit, i.e., an orbit based on actual observations. The
second 24 hours contain a predicted orbit. However, the orbit should be
continuous at the boundary between the real and predicted part.
Currently these Ultra rapid (IGU) products are generated twice each day at 
03:00 and 15:00 UTC and have a time-lag (time after the last observation used) 
of 3 hours.  Like the IGP (IGS Predicted) products the IGU products are usable 
for (near-) real-time applications. However, the average age of the IGU 
predictions is only 9 hours compared to 36 hours for the IGP products. 
This constitutes a significant improvement and the IGU products clearly 
perform much better than the IGP products (e.g. see 
 http://www.aiub.unibe.ch/acc/ or more directly 
 http://www.aiub.unibe.ch/acc/ps/rmsiguR.ps ).

The quality of the IGU orbits is estimated to be at the 20 cm level for
the part which would be used for (near-) real-time applications. This is
a very significant achievement and it is expected to improve even further
as more IGS stations start submitting hourly RINEX files.

As a consequence the IGP products will be discontinued. To enable everybody
to make a "clean" switch from IGP to IGU products we will allow for an 
overlap period of approximately 1 month. It is therefore planned to discontinue
the IGP products starting with GPS week 1092 day 0 (December 10, 2000).
This should give everybody enough time to adopt the IGU products.

The naming convention of the IGU products is:
  iguWWWWD_HH.EXT

Where: WWWW = GPS week
       D    = Day of week (0,...,6: Sun,...,Sat)
       HH   = Starting hour of the predicted part of the orbit.
              HH will be "00" for the IGU combination performed at 03:00 UTC.
              HH will be "12" for the IGU combination performed at 15:00 UTC.
       EXT  = Products extensions. Currently: sp3, erp, and sum.
 
       NOTE: WWWW and D reflect the day on which the orbit predictions start!

The IGS Ultra rapid products will be available in the following directories
(just like most other IGS products):
CDDISA: ftp://cddisa.gsfc.nasa.gov/pub/gps/products/WWWW
SIO   : ftp://lox.ucsd.edu/pub/products/WWWW 
IGN   : ftp://igs.ensg.ign.fr/pub/igs/products/WWWW
IGSCB : http://igscb.jpl.nasa.gov/pub/products/WWWW/ultra
AIUB  : ftp://ftp.unibe.ch/aiub/ultra_igs

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


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 Tim Springer                      Astronomical Institute, University of Berne 
 springer@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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