To date, tsunami detection and warning systems have been based on deep-water, pressure-sensor observations that determine changes in sea surface elevation and fluctuation on the coast, which are point measurements. Researchers observed after-the-fact that existing coastal current monitoring radar remote sensing systems were able to detect the tsunami signal and velocity as it approached both the coast of Japan and the Pacific Coast of the United States.

The primary purpose of HG radar observations are to tell real-time offshore ocean circulation, but after looking closely at records from a few of the 80 HF radars that operate along the US Pacific coast and along the coast of Japan, researchers were able to see tsunami-induced wave velocities.

Radars in Hokkaido in Japan show tsunami measurements in their records. In California, the Coastal Ocean Currents Monitoring Program, a network of coastal radar devices, were able to detect the March 11 tsunami. The radar could offer hours of advance warning in Japan, but less than a half-hour warning in California due to the steeper sea floor bathymetry. This was the first time that a tsunami has been tracked by radar, and could prove to be a useful means of detection for future incidents.

The radar detection results are outlined in this paper published in the journal Remote Sensing.