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Item type:Publication, Access status: without files , Simulation and detection of tsunami signatures in ocean surface currents measured by HF radar(2011-06-13); ; ; ; High-frequency (HF) surface wave radars provide the unique capability to continuously monitor the coastal environment far beyond the range of conventional microwave radars. Bragg-resonant backscattering by ocean waves with half the electromagnetic radar wavelength allows ocean surface currents to be measured at distances up to 200 km. When a tsunami propagates from the deep ocean to shallow water, a specific ocean current signature is generated throughout the water column. Due to the long range of an HF radar, it is possible to detect this current signature at the shelf edge. When the shelf edge is about 100 km in front of the coastline, the radar can detect the tsunami about 45 min before it hits the coast, leaving enough time to issue an early warning. As up to now no HF radar measurements of an approaching tsunami exist, a simulation study has been done to fix parameters like the required spatial resolution or the maximum coherent integration time allowed. The simulation involves several steps, starting with the Hamburg Shelf Ocean Model (HAMSOM) which is used to estimate the tsunami-induced current velocity at 1 km spatial resolution and 1 s time step. This ocean current signal is then superimposed to modelled and measured HF radar backscatter signals using a new modulation technique. After applying conventional HF radar signal processing techniques, the surface current maps contain the rapidly changing tsunami-induced current features, which can be compared to the HAMSOM data. The specific radial tsunami current signatures can clearly be observed in these maps, if appropriate spatial and temporal resolution is used. Based on the entropy of the ocean current maps, a tsunami detection algorithm is described which can be used to issue an automated tsunami warning message.Publicationtype: Journal Article22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , HF radar observation of a tsunami near Chile after the recent great earthquake in JapanA 9.0-magnitude undersea earthquake occurred near the coast of Japan on March 11, 2011, and generated a powerful tsunami, which propagated across the Pacific Ocean. The high-frequency (HF) surface wave radar is an operational tool for coastal monitoring worldwide. The oceanographic WERA HF radar located in Chile was in operation and provided measurements in real-time when the tsunami waves reached this region. For the first time impressive tsunami signatures of changing sea surface current velocities were observed by the HF radar system. The tsunami wave train can be clearly seen in the radar measurements. It was found to be significantly correlated with the water level measurements by tide gauges. © 2011 DGON.Publicationtype: Conference Paper23