The tsunami generated by the 2011 Tohoku-Oki earthquake was the first time that the velocity fields of a tsunami were measured by using high-frequency oceanographic radar (HF radar) and since then, the development of HF radar systems for tsunami detection has progressed. Here, a real-time tsunami detection method was developed, based on virtual tsunami observation experiments proposed by Fuji et al. In the experiments, we used actual signals received in February 2014 by the Nagano Japan Radio Co., Ltd. radar system installed on the Mihama coast and simulated tsunami velocities induced by the Nankai Trough earthquake. The tsunami was detected based on the temporal change in the cross-correlation of radial velocities between two observation points. Performance of the method was statistically evaluated referring to Fuji and Hinata. Statistical analysis of the detection probability was performed using 590 scenarios. The maximum detection probability was 15% at 4 min after tsunami occurrence and increased to 80% at 7 min, which corresponds to 9 min before tsunami arrival at the coast. The 80% detection probability line located 3 km behind the tsunami wavefront proceeded to the coast as the tsunami propagated to the coast. To obtain a comprehensive understanding of the tsunami detection probability of the radar system, virtual tsunami observation experiments are required for other seasons in 2014, when the sea surface state was different from that in February, and for other earthquakes.
Real-Time Tsunami Detection with Oceanographic Radar Based on Virtual Tsunami Observation Experiments