Characterization of GPS Multipath Errors in the Final Approach Environment

Michael S. Braasch

Abstract:	GPS is currently being considered as a possible replacement for the Instrument and Microwave Landing Systems. Differential carrier-phase tracking holds the potential to provide the sub-meter positioning accuracy which is required for Category III landings. However, before this technology reaches full maturity, a stumbling block remains. It is the effect of multipath. Multipath represents the dominant error source in a satellite-based precision approach and landing system. Since multipath errors are not common to the ground and airborne receivers, they are not eliminated through differential corrections. Although a multitude of GPS articles discuss the effects of multipath, most give little or uo insight into the particular problems associated with the final approach and landing environment. Unlike en- route navigation, the final approach environment brings the aircraft in close proximity to obstacles. In addition, multipath errors due to reflection and diffraction from the airframe itself are no longer negligible in the final phase of flight. This paper presents a comprehensive treatment of the problem. The impact of obstacle clearance surfaces is discussed and is shown not to eliminate the multipath threat. The sensitivity of multipath to airframe and antenna type is also presented.
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:	383 - 394
Cite this article:	Braasch, Michael S., "Characterization of GPS Multipath Errors in the Final Approach Environment," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 383-394.
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