Evaluation of the EGNOS Ionospheric Correction Model under Scintillation in Northern Europe

Terry Moore, Marcio Aquino, Sam Waugh, Alan Dodson and Chris Hill

Abstract:	The augmentation systems such as EGNOS aim to complement GPS (and GLONASS) with accuracy, integrity and availability, providing navigation services suitable for safety critical applications. The EGNOS System Test Bed (ESTB) has been transmitting an EGNOS-like signal from space since February 2000. This signal is currently available under the footprint of the Inmarsat AOR-E (Atlantic Ocean Region East) satellite and offers users the means to potentially address the issue of attainable performance, under varying tracking conditions. The EGNOS system Advanced Operational Capability (AOC) is scheduled for early 2003. Its Wide Area Differential (WAD) corrections include ionospheric grid delays based on GPS L1/L2 data. During and around the peak of the solar cycle, the effects of ionospheric disturbances such as scintillation were and are still being sensed, especially in the auroral geomagnetic region. For example, a significant geomagnetic storm was recorded in November 2001 and several other events have occurred since then. The impact of ionospheric scintillation on the performance of the WAD corrections has not yet been the subject of a detailed study in Europe. Short-lived ionospheric disturbances may degrade the ability of the EGNOS correction model to account for possible horizontal gradients in the Total Electron Content (TEC). It is necessary to assess the impact of these events, in particular regarding the integrity of the error model in EGNOS. This paper reports on investigations aiming to assess the EGNOS ionospheric model performance during periods of disturbed ionosphere, in particular during November 2001. The analyses are mostly based on the assessment of DGPS performance during these periods, with and without the aid of the EGNOS corrections. EGNOS correction data was kindly provided by the ESTB. Scintillation data from NovAtel/AJ Systems GSV4004 receivers and dual-frequency GPS data from the General Lighthouse Authorities (GLA) and the International GPS Service (IGS) stations were also used. A brief discussion on the possible development of warning mechanisms for the DGPS user is also presented.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1297 - 1306
Cite this article:	Moore, Terry, Aquino, Marcio, Waugh, Sam, Dodson, Alan, Hill, Chris, "Evaluation of the EGNOS Ionospheric Correction Model under Scintillation in Northern Europe," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1297-1306.
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