Consideration of impact factors on data acquisition for ocean radar with VHF band

An ocean radar with a VHF band is a useful tool for surveying coastal currents in a wide area. We have conducted a field observation of currents in Ariake Bay, the large inner sea located in the western part of Japan. Although the number of valid data acquired (hereafter, data acquisition) varies temporally and spatially, the mechanism of such variation is not yet well understood. Our aim in this study is to investigate the impact factor affecting data acquisition through field observations of current, salinity and wind in Ariake Bay. As a result, the data acquisition and the maximum measurement distance of the radar decreased owing to the decreases in salinity and wind speed. After receiving much rainfall, the data acquisition decreased rapidly in accordance with the decrease in surface salinity influenced by run-off from adjacent rivers and a flood control dike. Also, when wind speed became less than 2 m/s, the intensity of the signals received was not sufficient for the detection of current velocity. In conclusion, salinity and wind speed are important factors for steady-current observation using ocean radars.