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Modified Tomographic Estimation of the lonosphereusing Fewer Coefficients
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 Title & Authors
Modified Tomographic Estimation of the lonosphereusing Fewer Coefficients
Sohn, Young-Ho; Kee, Chang-Don;
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Ionospheric time delay is the biggest error source for single-frequency DGPSapplications, including time transfer and Wide Area Differential GPS (WADGPS).Currently, there are many attempts to develop real-time ionospheric time delayestimation techniques to reduce positioning error due to the ionospheric time delay.Klobuchar model is now widely used for ionosphehc time delay calculation forsingle-frequency users. It uses flat surface at night time and cosine surface atdaytime[1], However, the model was developed for worldwide ionosphere fit, it isnot adequate for local area single-frequency users who want to estimateionospheric time delay accurate1y[2]. Therefore, 3-D ionosphere model usingtomographic estimation has been developed. 3-D tomographic inversion modelshows better accuracy compared with prior a1gorithms[3]. But that existing 3-Dmodel still has problem that it requires many coefficients and measurements forgood accuracy. So, that algorithm has Umitation with many coefficients incontinuous estimation at the small region which is obliged to have fewermeasurements.In this paper, we developed an modified 3-D ionosphehc time delay modelusing tomography, which requires only fewer coefficients. Because the combinationsof our base coefficients correspond to the full coefficients of the existing model, ourmodel has equivalent accuracy to the existing. We confirmed our algorithm bysimulations. The results proved that our modified algohthm can perform continuousestimation with fewer coefficients.
ionosphere;local area ionospheric time delay;tomography;WADGPS;
 Cited by
Bradford W. Parkinson and James J. Spilker Jr., 'Global Positioning System : Theory and Applications', American Institute of Aeronautics and Astronautics, Inc, 1996

J.A.Klobuchar, 'Design and characteristics of the GPS ionospheric time delay algohthm for single frequency users', Proceedings of the IEEE Position Location and Navigation Symposium, November 1986

Zhizhao Lin and Yang Gao, 'Accuracy Analysis of 3-D lonospheric Tomography', I0N GPS 2002, 2002

T.D.Raymond, 'Compahsons of several ionosphehc tomography algorithms', Annales Geophysicae, vo1.13, no.12, 1995

Andrew J. Hansen, 'Tomographic Estimation of the lonosphere using Terrestrial GPS Sensors', Ph.D. dissertation, 2002.3, Stanford University

D. Bilitza, International Reference Ionosphere 2001, model/models/iri.html. 2001

Todd Walter, Andrew Hansen, Juan Blanch, Per Enge, Tony Mannucci, Xiaoqing Pi, Larry Sparks, Byron Ujima, Bakry El-Arini, Roland Lejeune, Mine Haeen, Eric Altshuler, Rob Fries and Aleck Chu, 'Robust Detection of lonospheric Irregulahties', I0N GPS 2000, 2000