Low-Cost GNSS Interferometric Reflectometry (GNSS-IR) Sensor for Potential Long-Term Coastal Sea Level Monitoring

Abstract. In the continued exploration of Global Navigation Satellite System (GNSS) technologies, remote sensing using interferometric reflectometry (IR) has emerged as a promising method for surface monitoring through the analysis of multipath signals. Due to this unique method of capitalizing an error source of GNSS signal to determine environmental parameters, this research aims to monitor coastal sea level by developing and assembling a low-cost GNSS-IR sensor system, and to compare its measurements with data from a traditional tide gauge. A u-blox F9P receiver in tandem with a u-blox ANN-MB-00 antenna oriented towards the first Fresnel Zone (FFZ) for optimal retrievals was connected to a solar-powered Raspberry Pi single-board computer. Remote device monitoring and GNSS data logging were done using an open-source web server hosted through PiTunnel. The acquired data was then processed through gnssrefl, employing advanced outlier removal, bias corrections, and height adjustments, thus accurately capturing sea level trends. The deployed station in Limay, Bataan, showcased continuous operation over a course of 15 days with minimum physical intervention and technical issues encountered. Meanwhile, the GNSS-IR measurements show strong alignment with the tide gauge record, with an RMSE of 3.115 cm, MAE of 2.240 cm, and a Pearson correlation of 0.997, indicating excellent performance in capturing sea level variations. From these results, it can be inferred that the GNSS-IR technique demonstrated through a low-cost and reliable sensor system is a viable alternative for long-term coastal sea level monitoring.