A.L. Dzvonkovskaya

High-frequency (HF) surface wave radars provide a unique capability to detect targets far beyond the conventional microwave radar coverage. Moreover the radars are functional equipment in modern radio oceanography and could contribute to the development and improvement of tsunami early warning systems. These radar systems can be installed at any coast with a shelf edge width of about 100 km to have sufficient time in order to detect approaching tsunami wave and to issue early warning message. This paper describes the simulation of tsunami travelling towards the coast and observed by HF radar at long ranges. A tsunami event is simulated using the oceanographic model HAMSOM (HAMburg Shelf Ocean Model), which has high spatial and temporal resolution and gives the ocean surface currents induced by an approaching tsunami. In this paper the data of the HF surface wave radar WERA (WEllen RAdar) are used; the radar was developed as an oceanographic low power radar to measure the wide ranges of ocean surface currents, waves, and wind. The tsunami current velocity is converted into frequency modulating signals and superimposed on measured antenna signals of the HF radar WERA. The changes due to tsunami induced currents influence radar backscattered spectra. The measured range-Doppler frequency radar spectra together with simulated tsunami currents have a specific "zigzag" feature, which changes from snapshot to snapshot according to tsunami movement. The tsunami detection technique is based on a statistical detection algorithm applied to the entropy filed of surface currents. This gives a possibility to issue an automated control of tsunami alert during real-time monitoring by the HF radar.