The Ionospheric Model Improvement for the Stanford WAAS Network

Yi-chung Chao, Yeou-jyh Tsai, Todd Walter, Changdon Kee, Per Enge, and Brad Parkinson

Abstract:	The Wide Area Augmentation System (WAAS) was invented mainly to solve the spatial decorrelation problem of GPS differential corrections. One of the important messages generated by the WAAS contains the ionosphere model parameters for single frequency users. However, ionospheric delay measurements of the GPS signal can be corrupted by the inter-frequency biases from both the transmitters (GPS satellites) and the receivers at the Wide Area reference stations (WRS). Therefore the ionosphere model generated by the WAAS master station will be both skewed and biased. This paper describes the characteristics of the biases and presents an inter-frequency bias estimation algorithm for creating an improved ionospheric delay model. This algorithm can be either implemented at each of the WRS’s individually or at the Wide Area Master Station (WMS). The data, taken at mid- afternoon during the winter season, show better than 0.5-meter consistency when compared using any one of several checking methods. The ionosphere model generated by the Stanford WAAS network, yielded smaller user ionosphere-related errors after applying the estimated biases to adjust the ionospheric delay measurement. The ionospheric delay models used for this study are a modified Grid algorithm and a Spherical Harmonics expansion.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	531 - 538
Cite this article:	Chao, Yi-chung, Tsai, Yeou-jyh, Walter, Todd, Kee, Changdon, Enge, Per, Parkinson, Brad, "The Ionospheric Model Improvement for the Stanford WAAS Network," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 531-538.
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