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

Abstract

26A Multi-frequency High Frequency (MHF) Radar system was designed and 27 developed by Wuhan University in 2007. This system can simultaneously operate at 28 four frequencies at most in the band of 7.5-25 MHz. This paper focuses on discussing 29 the performances of MHF radar system deployed along the coast of the East China 30 Sea based on comparisons with multi-depth ADCP data sets, which were obtained 31 from ADCPs deployed at different locations in August 2010 during a small storm. The 32 comparisons illustrate that radar-derived radial currents are correlated with ADCP 33 data at 2-4 m depth most, with correlation coefficients over 0.95 and RMS differences 34 less than 0.12 m/s for both operating frequencies. Bearing offsets at A, C and D points 35 are computed for different operating frequencies, with magnitudes of 0-11 degrees.36The capability of MHF radar to measure currents at different depths is explored. 37The results indicate that effective depth of current measurements by MHF radar 38 increases with decreasing operating frequency. A linear regression (with a regression 39 coefficient of 0.0576) of the responses in the mean effective depth on the predictors in 40 radio wavelength is obtained. The dominant semidiurnal and diurnal constituents are 41 also analyzed. The radial current amplitudes of M2 and K1 constituent are strong in 42 this area during this experiment. The residual currents vary with wind speed, with a 43 correlation coefficient of 0.52. We also yield a correlation coefficient of 0.79 between 44 non-tidal currents and the radial wind speed after clockwise rotating the wind vector 45 by about 50 degrees. 46 376 Barrick, D. E., 1972: First-Order Theory and Analysis of MF/HF/VHF Scatter from 377 the Sea. IEEE Trans. Antennas Propag., AP-20, 2-10.

Validation of Sensing Ocean Surface Currents Using Multi-Frequency HF Radar Based on a Circular Receiving Array

“…The results illustrate that the utilization of the circular receiving array based on phase direction-finding mode provides current measurements with CC values that vary from 0.85 to 0.96 and RMSE values that range from 0.07 m/s to 0.14 m/s at different locations. Similar levels of current measurement performance were preliminarily obtained compared to other types of HF radar that have been reported in previous literature [10,30]. This type of compact design and signal processing method provides a practicable way to generate HF radar remotely sensed current maps.…”

“…Because large hills surround the Shengshan and Zhujiajian radar sites, the azimuthal ranges of the two systems assessed by the percent coverage map are approximately 150 • . The field of view becomes larger than the previous type of MHF radar that was installed at the Shengshan site with typical 120 • in azimuth [30]. The improvement in the field of view also provides us with a direct way to evaluate the current measurement performance using a radar-to-radar comparison.…”

“…Then, every ten minutes, the MHF-C radar is able to simultaneously extract currents, waves and winds from the Doppler spectra of different frequencies. Preliminary results have already indicated that this mechanism has the ability to provide ocean surface current and wave maps with multiple operating frequencies for a number of parameters, such as radial currents, current vectors, significant wave heights and averaged wave periods [28][29][30].…”

Validation and Evaluation of a Ship Echo-Based Array Phase Manifold Calibration Method for HF Surface Wave Radar DOA Estimation and Current Measurement

“…From the output vector, the DOA of the radar returns can be estimated using a direction-finding approach [1]. Actually, the phase distortion exists in the receiving elements.…”

“…Up to now shore-based HF surface wave radars, which operate in the band from 3-30 MHz, have been extensively used for ocean surface current [1], wave [2], and wind measurement [3], as well as ship detection [4][5][6]. The capability of obtaining ocean parameters with a relatively high temporal resolution and a fairly extensive coverage makes HF radars suitable for oceanography research [7], hazard forecasting [8], coastal engineering [9], and maritime security [10,11].…”