Integrated GPS/Loran Receiver for ASF Propagation Studies

R. Hartnett, P.F. Swaszek, G. Johnson

Abstract:	The Federal Aviation Administration (FAA) has embarked on a study of Loran to evaluate the suitability of this long-range system in serving as an independent radio navigation (RNAV) backup to GPS. Loran's potential benefit to aviation hinges upon its ability to support Non-Precision Approaches (NPA), which equates to a Required Navigation Performance (RNP) of 0.3 nautical miles. Through FAA sponsoring, the U.S. Coast Guard Academy (USCGA) is responsible for conducting some of the tests and evaluations to help determine whether Loran can provide the accuracy, availability, integrity, and continuity to support NPA's in the National Air Space (NAS). A major part of assessing the suitability of Loran is in understanding the nature of Loran ground wave propagation over paths of varying conductivities and terrain. Propagation time adjustments, called "additional secondary factors (ASFs)," are used to adjust receiver times of arrival (TOAs) to account for propagation over non-seawater path(s). These ASFs vary both spatially and temporally, and unless understood and/or modeled, we lose accuracy and may not be able to guarantee a hazardously misleading information (HMI) probability of less than 1x10-7. In this paper we describe a method for measuring Loran Additional Secondary Factors. The Loran sensor is a DDC-based software Loran-C receiver that provides Loran-C TOA information relative to UTC. A Kalman filter is used to integrate ASF dynamics, geographic information, and GPS and Loran measurements into smooth maps of the ASF variations.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	968 - 977
Cite this article:	Hartnett, R., Swaszek, P.F., Johnson, G., "Integrated GPS/Loran Receiver for ASF Propagation Studies," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 968-977.
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