From L. Thu Nov 19 01:59:34 1998 From: L. (L.) Date: Thu, 19 Nov 1998 1:59:34 PST Subject: [IGSMAIL-2073] Re Message-ID: 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 ]