On the feasibility of ionospheric sounding with modern dual-frequency smartphones

GNSS measurements are recognized as a key technique for ionosphere monitoring. Such a goal is typically realized with datasets from global or regional networks of permanent stations, which provide, e.g., vertical total electron content maps. Despite the unquestioned role of such an approach, it still suffers from an irregular distribution of on-ground monitoring sites, limiting the precision of GNSS-based ionospheric products. A solution addressing this issue is to adopt dual-frequency measurements from low-cost devices, particularly those provided by GNSS chipsets embedded in modern smartphones. These ubiquitous devices can, theoretically, lead to the extreme densification of ionospheric information; however, their widespread use must be preceded by a detailed analysis of data properties and quality.

This still-open issue motivated us to investigate the applicability of ionosphere monitoring using a geometry-free linear combination (GF LC) series built of smartphone-acquired GNSS phase data. In the experiment, we used two smartphones: Google Pixel 7 and Xiaomi 15T Pro, which provide multi-system dual-frequency measurements. The smartphone results were validated against those provided by a high-grade receiver - Trimble Alloy. The dataset comprised GPS, Galileo, and BDS observations collected during three 8-hour sessions. We analysed the completeness and quality of the data, including the noise level, the number of cycle slips, and the consistency and accuracy of smartphone GF LC time series in comparison to the benchmark values. While the analysis confirmed the applicability of smartphone measurements for ionospheric studies, it also revealed the poorer quality of all analysed characteristics. Furthermore, we observe a substantial performance discrepancy between the tested mobile devices, which may pose a problem for their combined utilization.