Delivered-To: igsmail@igscb.jpl.nasa.gov Date: Wed, 13 Aug 2003 14:52:34 -0400 (EDT) From: Carey Noll Reply-To: Carey Noll To: IGSMail , IGLOSMail Subject: [IGSMAIL-4551]: 1864 Maidanak Range Bias Drifting Negative Message-ID: Sender: owner-igsmail Precedence: bulk ****************************************************************************** IGS Electronic Mail 13 Aug 11:52:36 PDT 2003 Message Number 4551 ****************************************************************************** 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@ilrs.gsfc.nasa.gov