Comparative Assessment of Low-Cost GNSS Interferometric Reflectometry (GNSS-IR) and Conventional Tide Gauges for Coastal Sea-Level Measurement

Global climate change drives critical shifts in coastal sea-level dynamics, necessitating the deployment of dense, high-temporal-resolution monitoring networks. To achieve this, GNSS interferometric reflectometry (GNSS-IR) has emerged as a robust technique for monitoring relative sea-level changes. The present study evaluates the performance of a low-cost, multi-band GNSS setup (employing u-blox ZED-F9P receivers) as an economically viable alternative to traditional infrastructure. The GNSS-IR system was installed at the Altata Bay pier (Mexico), and its measurements were validated against a conventional radar tide gauge located 75 m away on the same pier structure. Across five ∼24 h measurement campaigns, the equivalent sea level was retrieved using SNR-based inverse modeling. The low-cost system demonstrated high fidelity, yielding correlations exceeding 85% and RMSE values between 7.0 cm and 21.0 cm. Furthermore, robust statistical validation using the Fisher F-test (α=0.05) confirmed no significant differences in measurement variance between the low-cost GNSS-IR system and the reference tide gauge. These findings validate the concept that low-cost GNSS receivers are a scientifically reliable alternative for expanding coastal sea-level monitoring infrastructure.