A New Method for Multipath Calibration in GPS Carrier Phase Measurements Using a Pseudolite in an Anechoic Chamber

Jeremie Godet, Joel Dantepal, Michel Grondin, Daniel Belot, Lise Baudenon, Isabelle Sebbag

Abstract:	GPS carrier phase measurements’ accuracy is mainly limited by errors due to multipath. For instance, attitude determination of a vehicle using GPS carrier phase difference measurements is affected by the multipath errors in such a way that the accuracy of attitude angles measurements is usually above 0.3-0.4 degrees for a one meter long baseline. This paper presents a new method which is used for satellite on-board mitigating the effects of multipath and antennas bias in order to increase the accuracy of such measurements. This method has been developed in a way that it can easily be added at the end of the satellite integration chain and it allows the realisation of a complete cartography of the multipath and antennas bias errors in less than 5 hours with an accuracy depending on the quality of the anechoic chamber (usually less than 1 mm in phase measurements). One of the main advantages of the anechoic chamber is that it creates space-like conditions as far as multipath is concerned, that is to say that the only multipath that we take into account is the one created by the satellite itself (every outside measurements with real GPS signal are perturbed by external multipath). In order to validate this method several objects with simple geometric shapes have been added to create multipath. The results are precise and for instance, by comparing the multipath created by two objects with the ones created by these two objects separately, we have been able to isolate the very small interaction multipath between them (due to a double reflection on these two different objects). We have also been able to observe the multipath effect of kapton coatings which covers the satellite. Therefore this method has demonstrated an ability to provide precise information for multipath modelisation, even for the shorter multipaths which are the most difficult ones to include in a multipath modelisation software.
Published in:	Proceedings of the 1998 National Technical Meeting of The Institute of Navigation January 21 - 23, 1998 Westin Long Beach Hotel Long Beach, CA
Pages:	113 - 121
Cite this article:	Godet, Jeremie, Dantepal, Joel, Grondin, Michel, Belot, Daniel, Baudenon, Lise, Sebbag, Isabelle, "A New Method for Multipath Calibration in GPS Carrier Phase Measurements Using a Pseudolite in an Anechoic Chamber," Proceedings of the 1998 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1998, pp. 113-121.
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