[IGSMAIL-2073] Re

[L.]

IGS Electronic Mail      Thu Nov 19  1:59:34 PST 1998      Message Number 2073
******************************************************************************

Author: L. Wanninger
Subject: Re: Rogue Ionosphere Problem

Dear Colleagues,

In IGS Message 2071 Tim Springer and Markus Rothacher described TurboRogue 
data loss due to the current ionospheric conditions.

A closer look at some of the data files of equatorial stations from 
November 8, 1998 (DoY 312) reveals that in the equatorial region the
vertical Total Electron Content (TEC) reached a maximum of around 
80 TEC units (TECU) and that no small-scale ionospheric disturbances 
occurred on this day. Due to the equatorial anomalies the maximum rate 
of change of slant TEC exceeded the high value of 5 TECU/minute for 
some low elevated GPS satellites.

In general, this kind of ionospheric condition does not cause any tracking
difficulties of geodetic or navigation GPS receivers. Therefore, it can
be assumed that the observed data loss is really a problem of a 
specific receiver (or firmware) version.

Some RINEX-converters or software packages misinterpret a high rate 
of change of slant TEC as cycle slips. Since the rate of change of slant 
TEC under the current ionospheric conditions in the equatorial region can 
exceed a carelessly selected cycle slip detection threshold for a long 
period of time (hours), all observations are cycle slip flagged and finally 
disregarded. 

The "real" ionospheric difficulties caused by severe small-scale ionospheric
disturbances which affect the GPS-receiver signal tracking ability have not 
been reported yet in this solar cycle. They are still ahead of us and will
be most severe in the equatorial region between local sun set and local 
midnight. Their occurrence has a distinct seasonal/longitudinal 
dependence.



[Mailed From: Lambert Wanninger <wanning at Rcs1.urz.tu-dresden.de>]