Tsunami Detection and Parameter Estimation From GNSS-R Delay-Doppler Map
In this paper, a scheme is developed to detect tsunamis and estimate tsunami parameters from Global Navigation Satellite System-Reflectometry (GNSS-R) delay-Doppler maps (DDMs) of a tsunami-dominant sea surface. First, a procedure to determine tsunami-induced sea surface height anomalies (SSHAs) from DDMs is presented, and a tsunami detection precept is proposed. Subsequently, the tsunami parameters (wave amplitude, direction and speed of propagation, wavelength, and the tsunami source location) are estimated based upon the detected tsunami-induced SSHAs. In application, the sea surface scattering coefficients are unambiguously retrieved by employing the spatial integration approach (SIA) and the dual-antenna technique. Next, the effective wind speed distribution can be restored from the scattering coefficients. Assuming that all DDMs are of a tsunami-dominated sea surface, the tsunami-induced SSHAs can be derived with the knowledge of background wind speed distribution. In addition, the SSHA distribution resulting from the tsunami-free DDM (which is supposed to be zero) is considered as an error map introduced during the overall retrieving stage and is utilized to mitigate such errors from influencing subsequent SSHA results. In particular, a tsunami detection procedure is conducted to judge the SSHAs to be truly tsunami-induced or not through a fitting process, which makes it possible to decrease the false alarm. After this step, tsunami parameter estimation is processed based upon the fitted results in the former tsunami detection procedure. Furthermore, an additional method is proposed for estimating tsunami propagation velocity and is believed to be more desirable in real-world scenarios. The above-mentioned tsunami detection precept and parameter estimation have been tested with simulated data based on the 2004 Sumatra-Andaman tsunami event. The errors of estimated tsunami wave amplitude, propagation direction and velocity, wavelength, and source location are 0.03 cm, 1.16°, 1.45 m/s, 5.82 km, and (-0.22°N, -0.67°E), respectively.