Guangcai Li, Chiyu Long, Feng Wang, GNSS Research Center, Wuhan University, China

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The release of raw multi-GNSS data from Android smart devices opens up the opportunity of democratizing high-precision GNSS using super low-cost chipsets. We developed a method to integrate Android GNSS with accelerometer data to capture broadband vibration displacements at sub-centimeter resolution, which was firstly premised on the high-precision temporal synchronization among diverse Android sensors. Therefore, with the GPS/Galileo L1/L5 data collected with a low-profile patch antenna wired to a Xiaomi 8 smartphone, we time tagged the accelerometer data by calibrating a time shift between the two sorts of data. Despite this initial temporal alignment, the instability of the smartphone clock, as well as the sampling inconsistency between the accelerometer and the GNSS chipset, would still cause further synchronization errors, which were then estimated along with the displacement in the data fusion process. In this case, we presented that the accelerometer data could be synchronized with the GPS time at an accuracy of less than 10 ms, though no pulse-per-second signal from the GNSS chipset can be accessed by the smartphone accelerometers. Based on this achievement, a shake table test further showed that the displacements of the integrated Xiaomi 8 GNSS/accelerometer solution achieved an accuracy of 0.3 cm, which was a 42% improvement over that of the Android system time-based method, and their frequency bandwidth was increased from 0.5 Hz to 50 Hz. Moreover, an airgun active source experiment in a Yunnan earthquake-prone region verified this GNSS/accelerometer integration rooted in Android smartphones in monitoring micro-vibrations of larger than 2 cm/s2 ; encouragingly, the timing error of vibration recordings was less than 0.7 ms. We therefore demonstrate that Android multi-GNSS data can be synchronized and integrated effectively with smartphone accelerometers to resolve sub-centimeter vibrations, which will boost the application of super low-cost sensors in earthquake and structure monitoring.