Simulation and detection of tsunami signatures in ocean surface currents measured by HF radar
- 528 Downloads
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.
KeywordsOcean surface current HF radar Remote sensing Tsunami Ocean modelling
The authors would like to thank EADS and Atlas Elektronik for kindly providing the HF radar data sets acquired at Figueira, Portugal. This work has been supported by the German Ministry of Research and Education (BMBF) within its program “Geotechnologien” under the reference number 03G0659A.
- Dzvonkovskaya A, Gurgel KW, Rohling H, Schlick T (2008) Low power high frequency surface wave radar application for ship detection and tracking. Proc. Radar 2008 Conf. Adelaide, Australia, pp 654–659Google Scholar
- Dzvonkovskaya A, Gurgel KW, Pohlmann T, Schlick T, Xu J (2009a) Simulation of tsunami signatures in ocean surface current maps measured by HF radar. Proc. Oceans 2009 Conf. Bremen, GermanyGoogle Scholar
- Dzvonkovskaya A, Gurgel KW, Pohlmann T, Schlick T, Xu J (2009b) Tsunami detection using HF radar WERA: a simulation approach. Proc. Radar 2009 Conf. Bordeaux, FranceGoogle Scholar
- Gill EW (1999) The scattering of high frequency electromagnetic radiation from the ocean surface: an analysis based on bistatic ground wave radar configuration. Ph.D. thesis, Memorial University of Newfoundland, St. John’s, CanadaGoogle Scholar
- Gurgel KW, Barbin Y, Schlick T (2007) Radio frequency interference suppression techniques in FMCW modulated HF radars. Proc. IEEE/OES Oceans 2007 Europe, Aberdeen, Scotland, UKGoogle Scholar
- Hasselmann K (1971) Determination of ocean wave spectra from Doppler return from sea surface. Nat Phys Sci 229:16–17Google Scholar
- United States Government Accountability Office (2010) U.S. Tsunami Preparedness. GAO Report 10-490, April 2010Google Scholar
- Wait JR (1962) Electromagnetic waves in stratified media. Pergamon, New YorkGoogle Scholar