Shin'ichi Sakai

Coastal Current Observation in the Area of Abrupt Topographic Change with DBF Ocean Radar

A DBF ocean radar can detect the surface current pattern every 15 minutes. The tidal current and the residual current were investigated through the continuous observation of the DBF (digital beam forming) radar in the middle-west area of Ariake Bay in autumn 2005. For the validation of the surface current data by the DBF ocean radar the ship-board ADCP measurements were also conducted at spring tide. As the result of the comparison of both surface current data, the correlation coefficient and the standard error of the current speed are 0.89 and 7.23cm/s, and those of the current direction are 0.92 and 35.89 degree. The harmonic analysis of the long-term data by the DBF ocean radar clarifies the spatial pattern of the principal tides and the residual currents. The residual currents in 15days flow south to southeastward caused mainly by the tidal residual currents due to the topographic asymmetry.

Characteristics of Surface Currents around the Mouth of Isahaya Bay using DBF Ocean Radar

This study deals with the field observations on coastal surface currents by means of both Digital Beam Forming marine radar (DBF ocean radar) and Acoustic Doppler Current Profilers (ADCP) in order to realize characteristics of flow around the mouth of Isahaya Bay. In particular, the former has started since 2005. On the other hand, the latter has carried out seven times since 2001. As a result, it is found out that the feature of the M2 consituent flow detected by the DBF ocean radar was widely coincided well with other ADCP field observation data. Not only the river runoff in the head of Ariake Sound but also a flush flow from the sea-dike gate contribute to the surface currents around the mouth of Isahaya Bay significantly.

Long-term Real Time Monitoring System by DBF Ocean Radar and its Availability and Effectiveness

DBF ocean radar can detect surface currents widely with high resolution in all weather conditions. We developed 24-hours real-time oceanographic monitoring system, which based on automatic figuring system for surface currents and wireless communication system with high-speed packet communications (up to 384 bps). Figures of surface currents can be delivered every 15 minutes with time lag of about 45 minutes through the Internet. The Dragon System is feasible for emergency observation after sudden ocean accident such as oil spills because of high portability. Field observations showed a measurable rating is more than 90% within 15 km along the receiving beam lines. Amount of measuring points in one operation periodically change over time. Its fluctuations were related with tidal variability.