In the last few years, Android smartphones became the leading products within the GNSS mass-market world after the release of the Android Raw GNSS Measurements API, developed from Google, and the technological developments led by handset manufacturers. The latters result in multi-band and multi-GNSS chipset now embedded in common smartphones - e.g. Xiaomi Mi 8. The Google API, allowing the reconstruction of traditional GNSS observations, paved the way to the development of new and more precise GNSS-based applications for Android smartphones.
The aim of this research project is to assess the possibility of using GNSS observations from Android devices in the reconstruction of geophysical phenomena interesting the Earth surface and/or the ionospheric layer levereging on two variometric algorithms developed in the Geodesy and Geomatics Division: VADASE and VARION. In particular, VADASE (Variometric Approach for Displacement Analysis Stand-alone Engine) will be used to retrieve 3D velocity of a stand-alone receiver - Android smartphone in this case - in real-time, and VARION (Variometric Approach for Real-Time Ionosphere Observations) will allow the real-time estimation of sTEC (Total Electron Content) variations reletad to TIDs (Travelling Ionospheric Disturbances). The quality of GNSS measurements from Android smartphones, dependent on the extremely low-cost GNSS antenna used, requires the definition of data quality handling algorithms to avoid and exclude faulty measurements and/or cycle slip affecting the variometric phase observations used inside VADASE and VARION.
The research project results will be a reference study on whether or not Android GNSS data may be used in GEO Big Data analysis to densify the actual knowledge available in the case of geophysical events reconstruction.
Android raw GNSS measurements are nowadays commonly used to increase the location accuracy for different applications: increase real-time navigation, fitness, AR (Augmented-Reality) apps are only few examples. However, the possibility of using Android devices to support geophysical applications, especially in the field of GNSS seismology and ionosphere monitoring, is brand new and it started with the research published from the author of this proposal in [1]. The results of the proposed research project will represent a reference point for the GNSS community interested in developing GEO Big Data application and/or services relying on Android smartphone to add new and densified information to the actual localized data available in the case of any geophysical phenomena. Android devices are, indeed, a costless solution to increase independent data in the study of geophysical phenomena: the amount of Android smartphone compatible with the Google API - in particular the number of multi-band and multi-GNSS devices - is increasing quickly and will be able to support this kind of applications.
The innovation is not limited to the geophysical applications but this research project aims also at the definition of a methodology useful to detect faulty measurements and cycle slips often affecting carrier-phase measurements from Android devices. The quality assessment of carrier-phase measurements is challenging especially because of the phase ambiguity term which has to be properly estimated to reduce the constant bias term and increase the success rate of data handling algorithms. The increased noise on GNSS measurements from the low cost GNSS equipment embedded in a smartphone makes even harder the success of ambiguity fixing strategies. The methodology to be studied and developed in this proposed research project, being based on a time variation of carrier-phase measurements, has the scope to remove the uncertainty related to the phase ambiguity terms facilitating the detection of poor quality measurements.
[1] Fortunato, Marco, Michela Ravanelli, and Augusto Mazzoni. "Real-Time Geophysical Applications with Android GNSS Raw Measurements.", 2019.