[IGSMAIL-4551]: 1864 Maidanak Range Bias Drifting Negative

[Carey Noll]

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IGS Electronic Mail      13 Aug 11:52:36 PDT 2003      Message Number 4551
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Author: Van S. Husson, ILRS Central Bureau

Dear Colleagues,

This message is to alert the analysis community that
LAGEOS data from Maidanak-1 (Station 1864) has
been drifting negative since at least October
2001 at the rate of approximately -13mm/month. This
appears to be a classical clock frequency related 
problem. The site has been notified, and the source
of the error is still under investigation. 

A frequency error in SLR manifests itself as a 
range dependent error that will drift over time.

The system returned to operations in October 2001 after
being off-line for 10 months. Looking back using CSR Weekly
LAGEOS results, there are indications a similar problem 
could have existed at this site the 1st half of the year 
2000.

In addition, based on meteorological data analysis from 
Maidanak-1 (1864) and Maidanak-2 (1863), it appears all 
Maidanak-1 (1864) barometric data prior to October 2001 
was reading low by 6 millibars. 

Any comments can be sent to the ILRS Central Bureau
at CB at ilrs.gsfc.nasa.gov