Rapid initialization method in real-time deformation monitoring of bridges with triple-frequency BDS and GPS measurements

Abstract

Rapid initialization with ambiguity fixed resolution plays a key role in real-time Global Navigation Satellite Systems (GNSS) displacement monitoring of bridges. In this study, we propose a rapid initialization method with triple-frequency (TF) BeiDou Navigation Satellite System (BDS) and Global Positioning System (GPS) observations. The key step of this method is to form extra-wide-lane (EWL) ambiguity with TF BDS and GPS carrier-phase to reduce the ambiguity search space. In order to improve the speed of ambiguity resolution (AR) further, the strategies of fixing ambiguities in groups sequentially from long wavelength to the short and partial AR (PAR) with elevation and signal-to-noise ratio (SNR) criterions were proposed. Based on the real monitoring data on the Baishazhou Yangtze River Bridge, the AR efficiency was tested. The results illustrate that over 90% EWL ambiguities can be fixed by only single-epoch with TF BDS + GPS. After EWL ambiguity is fixed, the wide-lane (WL) ambiguity success rate could improve from 20% with dual-frequency (DF) BDS + GPS data to 70% with TF BDS + GPS data, 50–80% and 80–90% for the three stations respectively. Since the area of ambiguity search space is reduced by TF observations, the ambiguity search time decrased significantly compared with the DF BDS + GPS. In the Time-to-first-fix (TTFF) test, over 85% of epochs can complete the initialization process by only one epoch with one hour of 10 Hz TF BDS + GPS data. However, DF BDS + GPS has only 25%. As for the initialization time longer than two epochs, the counts of TTFFs of TF BDS + GPS are significantly less than that of DF BDS + GPS. Meanwhile, the integrated BDS and GPS can further enhance the geometry of satellites, which will be better for the precision improvement than the increase of signal frequencies.