Evaluating Radial Current Measurement of Multifrequency HF Radar with Multidepth ADCP Data during a Small Storm

A multifrequency high-frequency (MHF) radar system was designed and developed by Wuhan University in 2007. This system can simultaneously operate at four frequencies mainly in the 7.5-25-MHz band. This paper focuses on discussing the performances of an MHF radar system deployed along the coast of the East China Sea based on comparisons with multidepth ADCP datasets, which were obtained from ADCPs deployed at different locations in August 2010 during a small storm. The comparisons illustrate that radar-derived radial currents are correlated with ADCP data at mainly a 2-4-m depth with correlation coefficients over 0.95 and RMS differences less than 0.12 m s super(-1) for both operating frequencies. Bearing offsets at points A, C, and D are computed for different operating frequencies with magnitudes of 0 degree -11 degree . The capability of MHF radar to measure currents at different depths is explored. The results indicate that the effective depth of current measurements by MHF radar increases with decreasing operating frequency. A linear regression (with a regression coefficient of 0.0576) of the responses in the mean effective depth on the predictors in radio wavelength is obtained. The dominant semidiurnal and diurnal constituents are also analyzed. The radial current amplitudes of the M sub(2) and K sub(1) constituents are strong in this area during this experiment. The residual currents vary with wind speed, with a correlation coefficient of 0.52. A correlation coefficient of 0.79 between nontidal currents and the radial wind speed after a clockwise rotation of the wind vector by about 50 degree was obtained.