1 Hz GPS satellites clock correction estimations to support high-rate dynamic PPP GPS applied on the Severn suspension bridge for deflection detection

Abstract

The use of GPS for deflection and vibration detection in structures requires a data rate of 1 Hz or higher. We investigate the advantages of utilizing high-rate satellite clocks in a dynamic PPP processing strategy specifically applied to the measurement of the deflections of bridges. A dataset consisting of 96 globally distributed stations was used for GPS satellite clocks estimates. The undifferenced float ambiguity (FAmb) and the Zenith Total Delay (ZTD) parameters were first estimated using PPP in static mode. The 1 Hz clock products of the GPS satellites were then successfully estimated by applying the FAmb and tropospheric delays as constraints to the carrier phase. The techniques are compared to 30-s and 300-s clock corrections obtained from the IGS, as well as double differenced solutions, through two experiments. The first experiment uses a rotating-arm apparatus, consisting of a portable rig located at the University of Nottingham Ningbo China, incorporating a 4 m long arm that rotates at a constant speed through the use of an electric motor. The 1-s GPS satellite clocks gave the most precise and stable PPP solution. The second experiment investigates the dynamic deflections of the Severn Bridge's suspension cables and towers, estimated using both the PPP, using our 1-s clock corrections as well as the IGS's 30-s and 300-s clock corrections, and the double differenced (DD) GPS data processing method. Correlation coefficient and standard deviation of the PPP solution and DD solution reflect the bridge's displacement waveform consistency and accuracy, respectively. Numerical analysis of the correlation coefficient and standard deviation of the time series, processed with different satellite clock intervals, implies that improvement can be achieved by applying the short interval satellites clock products that we propose. The strong agreement of the waveforms, calculated from the high-rate PPP, with the DD and the bridge load data, demonstrates that high-rate PPP is a viable alternative to the DD method for structural monitoring and an optimal option at times when DD is impossible due to the failure or inappropriateness of using a reference station.