ASF Effect Analysis Using an Integrated GPS/eLORAN Positioning System

N. Luo, G. Mao, G. Lachapelle, and M.E. Cannon

Abstract:	This paper investigates the effect of the Additional Secondary Factor (ASF) on algorithms to integrate GPS and eLORAN under various application requirements. In order to support a flexible filtering scheme with multiple filtering options, the ASF is a critical parameter, in view of its stochastic properties such as spatial correlation. In order to gain an insight into ASF characteristics, ground Loran measurements gathered in kinematic mode under various conditions are used. These include measurements taken in the foothills of Canadian Rockies where ASF values and variations are relatively large. The ASF values, obtained using a time synchronized DGPS/Loran system, are analyzed. The large SNR drop in the mountainous part of the test is noted. Potential models to deal with the ASF in the integrated GPS/eLORAN Kalman filter in order to minimize its effect on position and to maintain reliable accuracy estimates are presented. Two cases are considered, namely Case 1 where the ASF is assumed known a priori from a lookup table with associated accuracy, and Case 2 where no a priori value is known. In addition to the ASF, other parameters taken into accounts that affect the filter input are GPS and Loran measurement errors.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	967 - 976
Cite this article:	Luo, N., Mao, G., Lachapelle, G., Cannon, M.E., "ASF Effect Analysis Using an Integrated GPS/eLORAN Positioning System," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 967-976.
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