Short-time observation of coastal currents with DBF radar

We have developed a DBF (Digital Beam Forming) radar which can complete one round observation of surface current every 15 minutes by a digital beam forming system. The predominant frequency is 41.9 MHz, range-directional resolution 500 m, maximum reach 25 km, azimuthal resolution 13-17/spl deg/ and velocity resolution 2.13 cm/s. We applied the DBF radar for current observation in the northern area of Ise Bay and compared the data with those collected synchronously by current meters set at 1 m and 2 m depth at two stationary points for eight days. The correlation coefficient between the DBF radar and the current meter at 1 m depth was 0.7-0.8 and the standard error 5-10 cm/s. In view of the fact that the measurement depth for the DBF radar was about 30 cm they seem to be coincided well. Next, we assimilated the continuous observation data of the DBF radar into a quasi three dimensional model of coastal currents by the nudging method in order to infer spatial and temporal changes of the currents. When the inferences of three-dimensional current were compared with the data gained by concurrently implemented ADCP spot observation at 4 measurement points, the current distribution for the surface-to-3 m depth layer was improved well as to speed and direction.