Subject: [IGSMAIL-0417] Re AC Recommendations/ITRF92
From: Jan Kouba
Date: Fri, 17 Dec 1993 15:13:58 PST

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IGS Electronic Mail      Fri Dec 17 15:13:58 PST 1993      Message Number 0417
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Author: Jan Kouba
Subject: Re AC Recommendations/ITRF92

Dear colleagues,

It was pointed out to us that IGSMAIL#263 coordinate set is not in
ITRF92 and it is not the best solution.  The results in ITRF92.SSC are
preferred because they include some additional VLBI/SLR/GPS solutions
and should be an improvement with respect to the #263 coordinates and
velocities.

According to the understanding at the Ottawa workshop that we should
adopt the best ITRF92 coordinate set and recommendation by IERS
Terrestrial Frame Section, we should adopt for our IGS processing the
ITRF92.SSC coordinate set, rather than the IGSMAIL#263 one.  We have
examined both coordinate sets and found them consistent (once
transformed to the same epoch) at the 1-cm level, with the exception of
the station YELL where a large height error (6 cm) exists in the ITRF92
coordinates.  Another, large height error was seen for DRAO, but this
station is not suggested for fixing/constraining.  Due to these large
errors at the above stations it is recommended that they are not fixed
or constrained.  (We have looked only at the 13 station set plus DRAO).
The large discrepancies at DRAO and YELL are being investigated.

Zuheir Altamimi of IERS/ITFS has kindly agreed to compile the 13
stations in an IGSMAIL message in a format similar to #263 for easier
reference and will be e-mailing it soon.  In the mean time, please
correct and take into considerations the change to ITRF92.SSC in the AC
Recommendations (IGSMAIL #414) .  The complete ITRF92.SSC can be gotten
by ftp either from

   URANUS.IGS.FR (192.33.147.79)

   login:    ITRF
   password: IERSPUB
   file:     ITRF92.SSC

or from 

   sideshow.jpl.nasa.gov (128.149.70.41, IGS Central Bureau)
   login: anonymous
   file:  /igscb/station/coord/itrf92.ssc

We apologize for the inconvenience and remain

                With Season's Greetings,

      Jan Kouba (for AC coordinator) & Jim Zumberge (for CB)