Behaviour of large scale structures of the electron content as a key parameterfor range errors in GNSS applications

The Total Electron Content (TEC) of the ionosphere is a key parameter for describing the ionospheric state. This paper deals with the large scale behaviour of TEC under low and high solar activity conditions. Large scale structures of the plasma density are formed by fundamental ionospheric processes mainly driven by solar radiation input, neutral winds and electric fields. The monitoring of large scale structures contributes to a comprehensive understanding of these coupling mechanisms which are rather complex particularly under perturbed geomagnetic conditions. The paper addresses techniques to monitor TEC with sufficient accuracy of a few TEC units (1016m-2) to measure large scale structures over Europe and over the polar areas. The availability of GPS data from global GPS receiver networks as e.g., those from the International GPS Service (IGS) is dense enough to generate TEC maps on a continuous base. A model assisted technique is briefly described for mapping TEC over the European and polar areas. A statistical estimation of horizontal TEC gradients reveals large scale gradients of up to about 6 TECU/1000 km under high solar activity conditions at an occurrence probability level of about 1%. Occasionally, during severe ionospheric storms this value may increase by a factor of 10 or even more. A close correlation of large scale gradients and the geomagnetic activity has been found giving the chance to forecast TEC gradient amplitudes by using predicted geomagnetic indices. Since TEC is proportional to first-order range errors in Global Satellite Navigation Systems (GNSS) such as the US GPS and the Russian GLONASS the study of the behaviour of this parameter has a practical meaning in GNSS based navigation and positioning. The paper addresses the close relationship between TEC and ranging errors in GNSS. Having in view Galileo, the planned Europe?s own global satellite navigation system, some aspects related to the mitigation of ionospheric propagation errors within the European Geostationary Navigation Overlay System (EGNOS) are discussed. Since EGNOS will augment the two above mentioned satellite navigation systems and make them suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels the ionospheric propagation errors have to be mitigated as much as possible.

[1]  Stefan Heise,et al.  Space weather effects on transionospheric radio wave propagation on 6 April 2000 , 2002 .

[2]  R. Leitinger,et al.  Ionospheric profilers using data grids , 2001 .

[3]  Richard Stamper,et al.  Nowcasting, forecasting and warning for ionospheric propagation: supporting databases , 2004 .

[4]  Jaume Sanz,et al.  New approaches in global ionospheric determination using ground GPS data , 1999 .

[5]  B. Wilson,et al.  Ionospheric specification algorithms for precise GPS‐based aircraft navigation , 2001 .

[6]  K. Davies,et al.  Studying the ionosphere with the Global Positioning System , 1997 .

[7]  Norbert Jakowski,et al.  TEC Monitoring by Using Satellite Positioning Systems , 1996 .

[8]  Norbert Jakowski,et al.  Geomagnetic Storm Effects on the Topside Ionosphere and Plasmasphere: A Compact Tutorial and New Results , 2000 .

[9]  Norbert Jakowski,et al.  Current developments in SWIPPA ‘Space Weather Impact on Precise Positioning Applications of GNSS’ , 2003 .

[10]  Xiaoqing Pi,et al.  Global ionosphere perturbations monitored by the Worldwide GPS Network , 1996 .

[11]  N. Jakowski,et al.  TEC monitoring by GPS - a possible contribution to space weather monitoring , 2001 .

[12]  S. Schlüter,et al.  Total electron content of the ionosphere during thegeomagnetic storm on 10 January 1997 , 1999 .

[13]  S. E. Pryse,et al.  Total electron content – A key parameter in propagation : measurement and use in ionospheric imaging , 2006 .

[14]  N. Jakowski.  Generation of TEC maps over the COST 251 area based on GPS measurements , 1998 .

[15]  Sandro M. Radicella,et al.  A family of ionospheric models for different uses , 2000 .

[16]  S. Schlüter,et al.  Space weather Effects Detected by GPS Based TEC Monitoring , 1998 .

[17]  J. Klobuchar.  Ionospheric Time-Delay Algorithm for Single-Frequency GPS Users , 1987, IEEE Transactions on Aerospace and Electronic Systems.

[18]  R. G. Musgrove,et al.  Ionospheric convection associated with discrete levels of particle precipitation , 1986 .

[19]  Bodo W. Reinisch,et al.  Comparison of ionospheric ionization measurements over Athens using ground ionosonde and GPS‐derived TEC values , 2003 .

[20]  Jaume Sanz,et al.  Neural network modeling of the ionospheric electron content at global scale using GPS data , 1997 .

[21]  H. Soicher,et al.  Time delay of transionospheric radio signals in a horizontally inhomogeneous ionosphere , 1994 .