[IGSMAIL-1679] Polar motion problems during Wk 0919

[Jim]

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IGS Electronic Mail      Thu Sep  4 11:21:39 PDT 1997      Message Number 1679
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Author: Jim Ray, Earth Orientation Dept., USNO
Subject: Polar motion problems during Wk 0919

During the week of 0919 (17-23 August) and for the first 3 days of week
0920, data were not available for most of the IGS fiducial stations at the
time that the IGS combined Rapid products were produced.  A problem at the
JPL Regional Data Center delayed data transmittal for 7 of the 13 fiducial
sites and no data have been available from TROM since week 0890.  Thus,
only 4 or 5 fiducials were usable for the Rapid combinations: ALGO,
HART/HARK, KOSG, WTZR, and YELL.  Subsequently, most of the missing JPL
data was restored and was used in the Final analyses.

The reduced fiducial network significantly degraded the quality of the IGS
Earth orientation products because of the more poorly defined terrestrial
reference frame.  This has been evident in the IERS Bulletin A values for
polar motion.  With the replacement in today's Bulletin A (04 Sept.) of IGS
Rapid polar motion values by Final values for week 0919 the effects are
quite noticable.  Both coordinates have shifted by more than 0.5 mas during
that week, with day-to-day variations up to ~1.0 mas.

This message is informational only and to illustrate our reliance upon the
IGS.  The ongoing need for high-quality data from independent techniques
is clear.


[Mailed From: Jim Ray (USNO 202-762-1444) <jimr at Maia.usno.navy.mil>]