A New Method for Monitoring the Earth's Ionospheric Total Electron Content Using the GPS Global Network

Anthony J. Mannucci, Brian D. Wilson, and Charles D. Edwards

Abstract:	The global positioning system satellites and a world-wide network of dual-frequency GPS receivers can be used to measure ionospheric total electron content (TEC) on global scales. A new method for generating global TEC maps is described. This method uses a Kalman-type filter and random-walk process noise to generate TEC maps at time intervals of one hour or less. The maps utilize a locally-supported vertical TEC function (called “TRIN”) based on tessellation of the sphere into 1280 spherical triangles. The 642 vertices of the triangles are assigned a TEC value estimated from the data and the TEC within each tile is computed by linearly interpolating between vertex TEC values. The previous approach used a single- batch filter requiring an averaging time of 6-12 hours before a map could be obtained; the TEC data was fitted to a surface harmonic expansion which did not follow local TEC variations accurately. Both approaches use a spherical thin-shell elevation mapping function to convert all station-to-satellite TEC measurements to equivalent vertical TEC at a unique shell intersect point. The new maps follow diurnal TEC variations over a single site to within a few TECU as measured by established single-site GPS calibration techniques. In a global-scale simulation using the Bent ionosphere model, the TRIN fit reproduces the simulated data set to within 5 TECU over 70 percent of the globe. Errors exceeding 10 TECU are seen in the daytime-peak regions within the equatorial bulge. Methods for improving the accuracy of the maps are discussed.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	1323 - 1332
Cite this article:	Mannucci, Anthony J., Wilson, Brian D., Edwards, Charles D., "A New Method for Monitoring the Earth's Ionospheric Total Electron Content Using the GPS Global Network," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 1323-1332.
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