Generalization of the Dual Frequency Method of Multipath Calibration for Global Reference Networks

R.B. Harris, E.G. Lightsey

Abstract:	The Dual Frequency Method, or DFM, creates a model of multipath at static reference stations. The DFM uses a combination of pseudorange and carrier phase observations to both isolate multipath and remove the influence of the ionosphere delay. The method also includes spatial processing that removes biases introduced by use of carrier phase observations. The DFM can be extended in two fundamental ways. First, the original formulation of the DFMdescribes how to isolate multipath for pseudorangeminus carrier phase multipath on L1. The DFM can also be applied to a number of other observation combinations. More combinations are possible using the new civilian GPS signal, L2C. An application that is part of the GPS Toolkit (GPSTk) provides a means to both apply and explore the family of multipath combinations. Any linear combination of range-type observables will contain a bias, derived from the observables involved. Not only carrier phase observables but also pseudorange observables contain biases. The DFM describes a processing technique for removing the biases when the linear combinations are organized by overhead pass. The technique requires finding the intersections of the passes. Prior investigations have numerically computed the intersections. An analytic solution to that search exists that is based on simplified dynamics of the GPS satellites. The analytic solution not only finds intersections for passes relative to given site’s overhead passes, but also generally for any site on the surface of the Earth. The analytic solution has the potential to produce intersection solutions that agree with the numerical solution to within fractions of a degree, when measured with azimuth and elevation. However that difference can grow large to even 2 degrees as satellites vary from the nominal GPS orbit.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	2914 - 2924
Cite this article:	Harris, R.B., Lightsey, E.G., "Generalization of the Dual Frequency Method of Multipath Calibration for Global Reference Networks," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 2914-2924.
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