Multipath Mitigation for Bridge Deformation Monitoring

Abstract

GPS carrier phase multipath with varying amplitudes of up to several centimetres and periods of couple of minutes is a major error source, which affects the correct interpretation of bridge deformation. In this paper, a recursive adaptive filtering (AF) algorithm has been employed to mitigate multipath signature in the coordinate time series of GPS solutions. In order to maximise the suppression of the multipath signature, exact alignment of the input time series into the AF system is crucial. An algorithm using the cross-correlation coefficient of day-to-day GPS coordinate time series is presented to align GPS coordi-nates. To isolate multipath from the contaminated GPS coordinate time series, relative displacements cal-culated from the accelerations sensed simultaneously with GPS receiver by a triaxial accelerometer housed in a specially designed cage is used as the reference signal sequence within the AF system. Associated al-gorithm for the relative velocity and displacement calculation is also introduced in the paper. It demon-strates that it is possible to achieve millimetre positioning accuracy by the AF approach and an integrated sensor system of GPS receiver and triaxial accelerometer.