Statistically Optimized In-Flight Estimation of GPS Carrier Phase Multipath for LEO Satellite Attitude Determination

Stephen Hodgart and Ronald Wong

Abstract: Measurement of the GPS carrier phase difference between multiple antennas on a satellite offers a fast low-cost system for the determination of its attitude. However, an acceptable system requires mitigation of the error due to carrier phase multipath. The UoSat12 low Earth orbit satellite was employed to investigate this effect for in-orbit measurements. The disparity between GPS measurements and independent computed reference phase differences constituted the raw data for constructing a multipath error map. Processing found substantial errors—an estimated multipath error lying between peaks of 43.9 mm and 42.6 mm with an rms value of 9.8 mm. Starting from conventional spherical harmonics and least square estimation, a novel method eliminates the effect of line bias variation and also determines the actual map error, i.e., the difference between true and estimated multipath. Selective optimization of choice of harmonics minimizes this error, which here is estimated to be 1.0 mm (1 sigma).
Published in: NAVIGATION, Journal of the Institute of Navigation, Volume 53, Number 3
Pages: 181 - 202
Cite this article: Hodgart, Stephen, Wong, Ronald, "Statistically Optimized In-Flight Estimation of GPS Carrier Phase Multipath for LEO Satellite Attitude Determination", NAVIGATION, Journal of The Institute of Navigation, Vol. 53, No. 3, Fall 2006, pp. 181-202.
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