Preliminary comparisons of sea current velocity vector measurements by a nautical X-band radar and moored ADCP

Non-coherent X-band radars are promising tools for monitoring and investigation of surface currents at distances of up to 7 km from the observation point. One of the limiting conditions of their use is the lack of experimentally confirmed investigations of accuracy of such measurements. This article is aims at filling this gap. For radar measurements we used standard navigation radar "River" (Micran) adapted for oceanographic purposes. The radar was installed on the Black Sea shore near Gelendzhik. For radar data processing we used an algorithm presented in (Ivonin et al., 2011), which allows to determine the velocity vector of currents in the case of sea wave heights greater than 1 m. The algorithm draws on works (Young et al., 1986; WaMoS II, 2003) and uses a sequence of amplitude radar images of sea surface acquired in increments of about 2 s. The modulation mechanisms manifest signals from the crests of long surface gravity waves, which becomes visible in radar images. After processing the latter in the spectral space, using the dispersion relation for surface gravity waves one may determine the radial components of current velocity in several directions, and then restore the vector velocity. The verification of the radar measurements of currents was performed by an acoustic Doppler current profiler (ADCP), located at the mooring station at a depth of 23 m, and 1 km away from the radar. The radar sensed the current near ADCP with averaging over the area of 0.5 km x 0.5 km. For a storm event, which lasted 5 days, 23-28 September, 2013, currents with amplitudes of 10 to 80 cm/s were registered. During this period the direction of currents changed by 180°. It was found that the accuracy of the radar measurements with respect to ADCP was 20 cm/s for the amplitude and 20° for the direction. These values are in agreement with the declared characteristics of the oceanographic radars WAMOS II.