Transforming Coastal GNSS Stations Into Tsunami Gauges With Adaptive Window Interferometric Reflectometry

While global navigation satellite system interferometric reflectometry (GNSS-IR) has been widely applied to monitor the water levels in lakes, rivers, tides, and storm surges, its potential for detecting high-dynamic waves such as tsunamis remains under-explored. In this study, we propose a near-real-time GNSS-IR tsunami monitoring framework that simultaneously inverts sea level, vertical sea-level velocity, and acceleration using an adaptive window. This approach is validated with GNSS data from the 2022 Tonga tsunami, demonstrating the ability to detect tsunami waves of approximately 0.5 m in amplitude and 40 min in period. The correlation with tide gauge data is 62.9%. Furthermore, we find that the observation conditions required for tsunami monitoring are stricter than those for tidal measurements, at least six available satellite arcs are required in a one-hour window. As a result, among 84 GNSS sites assessed along the Pacific Rim, 29 are deemed capable of effective tsunami monitoring, while others are only available for observing tides and storm surges.