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Date: Thu, 30 Mar 2000 18:14:44 +0200 (MET DST)
From: tim.springer@aiub.unibe.ch
Subject: [IGSMAIL-2771]: IGS Navigation solutions
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IGS Electronic Mail      30 Mar 08:14:49 PST 2000      Message Number 2771
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Author: Tim Springer


Dear IGS colleagues,

A small change has been made to the precise navigation solutions which are
routinely generated in the IGS combinations, both final and rapid.
The station of USUD (Usuda, Japan) has been replaced by the station 
TOW2 (Townsville, Cape Ferguson, Queensland, Australia).
This change was deemed necessary because since January 19, 2000 the 
data of USUD has been unusable for the 15 minuted sampled point positioning.
Notice, however, that for normal processing the data of USUD is of 
sufficient quality. 

The main problem with the USUD data is that cleaning of the data on the 
zero-difference level is very difficult. This is an artifact caused by 
the way the 30 second observations are generated from the 1 second data. 
USUD is tracking at 1 second to avoid the problems which the ROGUE SNR 
receivers have with high ionospheric activity 
(see IGSMAIL numbers 2071 and 2761).

The station TOW2 has been selected first of all because of its geographical
area (southern hemisphere!) and secondly because of its excellent availability 
and data quality. 

Kind regards,
         Tim Springer
         IGS AC Coordinator