Narrow Results

A new system for directional wave spectrum observation was developed by improving the Nationwide Ocean Wave information network for Ports and HArbourS (NOWPHAS). Either Doppler Type Wave Directional Meter (DWDM) or Wave Gauge Array System is adopted for wave observations. Directional spectra are estimated by EMLM method for DWDM and EMEP method for array system. For the convenience, the obtained directional spectra are expressed as the frequency banded wave heights and directions corresponding to the wave spectrum. Examples of annual statistics of the directional wave spectra at three typical NOWPHAS wave stations are introduced in this paper.

Observed profiles of tsunami caused by the 2003 Tokachi-off Earthquake at 10 offshore wave gauges and 23 coastal tide stations were compiled and analyzed. Comparison of offshore wave and coastal tide data was conducted in wave-to-wave analysis bases and spectrum analysis bases. The tsunami amplification ratio between offshore station and coastal tide station varied due to seabed topography induced natural frequency difference. The frequency spectrum response was obtained at those harbors. The correlation analysis among the sea-surface fluctuation, on-off-shore current and long-shore current was also conducted at offshore wave stations.

Development and improvement of the International Tsunami Monitoring System is getting more important after the 2004 Sumatra-Off-Earthquake Tsunami disaster. Till now, tsunami monitoring system has been developed and established based on observation network of strong ground motion only. Nevertheless, earthquake vibration data may give us incorrect tsunami forecasting, for the strength of the vibration and the tsunami energy are not exactly proportional. Therefore, offshore and coastal direct tsunami-wave profile observation system should be included in the monitoring system. This paper introduces basic design of the future tsunami monitoring system using newly developed GPS buoy system and other coastal and on-site sensors. Method of real-time tsunami data processing system is also introduced.