Title: Estimation of Absolute Ionospheric Delay Exclusively through Single-Frequency GPS Measurements
Author(s): Clark E. Cohen, Boris Penm and Bradford W. Parkinson
Published in: Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992)
September 16 - 18, 1992
Albuquerque, NM
Pages: 325 - 330
Cite this article: Cohen, Clark E., Penm, Boris, Parkinson, Bradford W., "Estimation of Absolute Ionospheric Delay Exclusively through Single-Frequency GPS Measurements," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 325-330.
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Abstract: Traditionally, ranging errors due to the ionosphere have been corrected through dual-frequency measurements. Single-frequency users have resorted to ionospheric modeling derived from broadcast parameters to remove roughly 50% of the ranging error. We report new experimental results in which we have extracted the ionospheric delay by measuring the relative divergence between the GPS code and carrier. The ionosphere is a dispersive medium subject to the well-known inverse frequency-squared characteristic. The phase and group velocities of a signal propagating through the ionosphere depart from the speed of light in a vacuum by equal and opposite amounts directly proportional to the integrated electron number density. Differencing the code and carrier observables yields a differential range measurement (ionospheric divergence) proportional to the total electron content but subject to an unknown initial offset between code and carrier phase. By observing changes in the ionospheric divergence with satellite elevation angle (obliquity), a receiver may estimate the absolute ionospheric delay for each satellite in view along with the local ionospheric density and the absolute offset between code and carrier. This estimation technique offers single-frequency users additional leverage to increase accuracy, both in absolute and differential operation. Furthermore, when applied to differential base station measurements, the technique may augment broadcast differential corrections, especially for wide-area operation.