Japan has high risk of large-scale earthquakes occurring around coasts, which generate tsunamis generally. Offshore tsunami detection is effective for prevention and reduction of human loss by the tsunami. GPS tsunami detection system is actually established in Japan. Further, recently a monitoring system with high frequency (HF) radar, which observes currents on the ocean surface mainly, is expected to detect tsunamis in deeper seas.
　In the ocean surface, there are many kinds of currents due to tides, wind, wave as well as tsunamis. Especially, wind-driven currents may be important for tsunami detection with the HF radar, because they are in a similar range of tsunami period and are obstacles for accurate estimation of tsunami-induced current.
　In this study, two type systems for removing wind-driven currents from data obtained in the HF radar. In the system measurement data of current and wind at any points is utilized to estimate the spatial currents are demonstrated. The other is the self-contained estimation system of wind-driven currents. In the system, the ocean winds are estimated with the analyzed wave height and period from the HF radar data and the Sverdrup-Munk-Bretschneider’s (SMB) method, calculating the wave height and period from wind duration and fetch. Using the estimated winds, the wind-driven currents are calculated by employing the theoretically derived surface share force.