Journal : Acta Geophysica
Article : Effects of ionospheric horizontal gradients on differential GPS

Authors :
Błęcki, J.
Space Research Centre, Polish Academy of Sciences, Warszawa, Poland,,
Chukwuma, V.U.
Department of Physics, Olabisi Onabanjo University, Ago-Iwoye, Nigeria,,
Krankowski, A.
Institute of Geodesy, University of Warmia and Mazury in Olsztyn, Poland,,
Abdullah, M.
Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia,,
Abstract : This paper outlines the effect of horizontal ionospheric gradients on transionospheric path propagation such as for the case of GPS signals. The total electron content (TEC) is a function of time of day, and is much influenced by solar activity and also the receiving station location. To make the model applicable for long baselines, for which the ionosphere is not generally well correlated between receiving stations, the ionospheric gradients should be taken into account. In this work the signal path is determined using a modified ray-tracing technique together with a homing-in method. Results show that horizontal gradients can have a significant effect on GPS positioning for both single station positioning and differential GPS. For differential GPS, the ionospheric delay can, however, be either increased or decreased compared with the case of no gradient, depending on the gradient direction.

Keywords : ionosphere, ionospheric gradients, GPS, ray-tracing, TEC,
Publishing house : Instytut Geofizyki PAN
Publication date : 2007
Number : Vol. 55, no. 4
Page : 509 – 523

: Abdullah, M., H.J. Strangeways and D.M.A. Walsh, 2003, Accurate ionospheric error correction for differential GPS, 12th Int. Conf. on Antennas and Propagation, ICAP 2003, Exeter, UK.
Afraimovich, E.L., N.P. Perevalova and S.V. Voyeikov, 2002, Traveling wave packets of total electron content disturbances as deduced from global GPS network data,
Bilitza, D., 2001, International Reference Ionosphere 2000, Radio Science 36, 2, 261-75.
Bounsanto, M.J., 1999, Ionospheric storms – A review, Space Sci. Rev. 88, 563-601.
Cannon, P., and R. Norman, 1997, The relative performance of numeric and analytic ray-tracing, 7th Int. Conf. on HF Radio Systems and Techniques, Nottingham, UK, 145-148.
Chen, X., H. Landau and U. Vollath, 2003, New tools for network RTK integrity monitoring, ION GPS 2003, The Institute of Navigation, Portland, USA.
Christie, J.R.I., P.Y. Ko, B.S. Pervan, P. Enge, J.D. Powell and B.W. Parkinson, 1999, Analytical and experimental observations of ionospheric and tropospheric decorrelation effects for differential satellite navigation during precision approach, ION GPS-99, The Institute of Navigation, Nashville, TN, USA.
Coster, A.J., J.C. Foster, P.J. Erickson and F.J. Rich, 2001, Regional GPS mapping of storm enhanced density during the 15-16 July 2000 geomagnetic storm, ION GPS 2001, The Institute of Navigation, Salt Lake City, UT, USA, 2531-2539.
Foster, J.C., 1998, Storm time plasma transport at middle and high-latitudes, J. Geophys. Res. 98, 1675-1689.
Foster, J.C., 2000, Quantitative investigation of ionospheric density gradients at mid-latitudes, The 2000 National Technical Meeting, The Institute of Navigation, Anaheim, CA.
Hargreaves, J.K., 1992, The Solar-Terrestrial Environment: An Introduction to Geospace – The Science of the Terrestrial Upper Atmosphere, Ionosphere and Magnetosphere, Cambridge University Press, New York, 420 pp.
Hernandez-Pajares, M., J.M. Juan, J. Sanz and O.L. Colombo, 2000, Application of ionospheric tomography to real-time GPS carrier-phase ambiguities resolution at scales of 400-1000 km and with high geomagnetic activity, Geophys. Res. Lett. 27, 2009-2012.
Hernandez-Pajares, M., J.M. Juan and J. Sanz, 2006, Medium-scale traveling ionospheric disturbance affecting GPS measurements: spatial and temporal analysis, J. Geophys. Res. 111, A07S11, doi:10.1029/2005JA011474.
Ho, Y.H., A.F.M. Zain, M. Abdullah, A.G. Ramli and W.S.W. Hassan, 2002, Equatorial TEC variations during the geomagnetic storm of July 15-17, 2000, 27th General Assembly of URSI, Maastricht, the Netherlands, 4 pp.
Ioannides, R.T., and H.J. Strangeways, 2000, Ionosphere-induced errors in GPS range-finding using MQP modelling, ray-tracing and Nelder-Mead optimisation, Millennium, Confer. on Antennas and Propagation, AP2000, Davos, Switzerland, 404-08.
Ioannides, R.T., and H.J. Strangeways, 2002, Rigorous calculation of ionospheric effects on GPS Earth-Satellite paths using a precise path determination method, Acta Geod. Et Geophys. 37, 281-292.
Nelder, J.A., and R. Mead, 1965, A simplex method for function minimization, The Computer Journal 7, 308-313.
Orus, R., M. Hernandez-Pajares, J.M. Juan and J. Sans, 2003, Effects of TIDs on the interpolation of real-time ionospheric corrections within mid-latitude GPS networks. Paper presented at Atmospheric Remote Sensing using Satellite Navigation Systems, URSI, Matera, Italy.
Rieger, M., and R. Leitinger, 2002, The effect of travelling ionospheric disturbances (TIDs) on GNSS user systems, 27th General Assembly of URSI, Maastricht, The Netherlands.
Rios, V., N. Jakowski, M. Santillan and C. Medina, 1999, Determination of horizontal gradients of ionization over Argentina with differential Doppler measurements, Adv. Space Res. 24, 1613-1617.
Strangeways, H.J., 2000, Effect of horizontal gradients on ionospherically reflected or transionospheric paths using a precise homing-in method, J. Atm. Terr. Phys. 62, 1361-1376.
Strangeways, H.J., and K. Nagarajoo, 2005, 3D gradient effects on transionospheric paths (such as from GPS) determined by ray-tracing in a 3-D IRI ionosphere. Paper presented at 2nd European Space Weather Week ESWW II, ESAESTEC, Noordwijk, The Netherlands, 14-18 November 2005. Online at:
Strangeways, H.J., M. Abdullah and D.M.A. Walsh, 2003, A method for improving the accuracy of differential GPS positioning, Paper presented at 3rd COST 271 Workshop in Spetses, Greece, 23-26 September 2003, and publ. on Conf. Proc. CDROM.
Wanninger, L., 2004, Ionospheric disturbance indices for RTK and network RTK positioning, ION GPS 2004, Institute of Navigation, California, USA.
Warnant, R., S. Stankov, J.C. Jodogne and H. Nebdi, 2002, The monitoring of the ionospheric activity using GPS measurements. Paper presented at 2nd COST 271 Workshop in Faro, Portugal, 1-5 October 2002, and publ. on Conf. Proc. CDROM.
Qute : Błęcki, J. ,Chukwuma, V.U. ,Krankowski, A. ,Abdullah, M. ,Abdullah, M. , Effects of ionospheric horizontal gradients on differential GPS. Acta Geophysica Vol. 55, no. 4/2007