Simulation of tsunami signatures in ocean surface current maps measured by HF radar

The high frequency (HF) surface wave radar has a unique capability to monitor the coastal environment far beyond the conventional microwave radar coverage. The HF radar could contribute to the development and improvement of Tsunami Early Warning Systems. Bragg-resonant backscattering by ocean waves with half the electromagnetic radar wavelength allows measuring the ocean surface current at distances up to 200 km. The developed software package allows reconstructing an ocean surface current map of the area observed by HF radar based on the radar range-Doppler spectrum processing. In case of an approaching tsunami, a strong ocean surface current signature can be observed by the radar when the tsunami wave enters the shelf edge. In order to simulate the signals seen by an HF radar in case of a tsunami travelling towards the coast, the tsunami induced current velocity is calculated using the oceanographic HAMburg Shelf Ocean Model (HAMSOM) model, then converted into modulating signals, and superposed to the measured radar backscatter signals. After applying conventional signal processing techniques, the radar spectra include the simulated tsunami wave. The surface current map based on these spectra has a pattern, which changes very quickly in the shelf area before the tsunami wave reaches the beach. Specific radial tsunami current signatures are clearly observed in these maps. If the shelf edge is far off the coast sufficiently then the first appearance of such signatures can be monitored by an HF radar system early enough to issue a warning message about an approaching tsunami.