Assessment of GNSS-IR performance using multi-GNSS and multi-frequency SNR data from smartphones

Smartphones are equipped with embedded Global Navigation Satellite Systems (GNSS) chips that support multiple satellite systems, enhancing precision in positioning, navigation, and timing services. The introduction of GNSS Interferometric Reflectometry (GNSS-IR) leverages these capabilities by analyzing multipath signals and reflections to estimate surface properties more accurately. Given their multi-GNSS and multi-frequency capabilities, along with lower cost and greater portability compared to traditional geodetic receivers, smartphones hold significant potential for application in GNSS-IR technologies. In this study, we conducted a three-day experimental evaluation, observing for six hours each day to assess the accuracy of reflector height and change estimations from multi-frequency multi-GNSS SNR data provided by geodetic receivers and smartphones. The setup included two CHC i90 Pro geodetic receivers and two Samsung Galaxy Note 20 Ultra smartphones, positioned in both zenith-looking and nadir-looking orientations, facilitated by an experimental setup developed under TÜBİTAK project number 121Y348. Our analysis focused on the number of valid estimations, peak-to-background noise ratio (PBNR) values, and the accuracy of reflector height and height difference estimations with satellite-based and frequency-based assessments. According to the results, geodetic receivers consistently outperform smartphones in data collection stability for GNSS-IR applications. We also found that the platform orientation of smartphones (flat, inverted, or inclined) has a minimal impact on the accuracy of GNSS-IR estimations, and the most reliable smartphone data is obtained from GPS satellites. Furthermore, using signals with wavelengths shorter than 20 cm in smartphone-based GNSS-IR studies provides better results and offers a cost-effective method for long-term monitoring of climatological parameters such as snow depth, sea level, and vegetation height.