Ocean Wave Parameters and Nondirectional Spectrum Measurements Using Multifrequency HF Radar

HF radars have been extensively used for current observation. However, wave measurement with HF radars is challenging mainly due to the limited measurable range of wave height using a single operating frequency. In order to obtain robust wave measurements in complex and various sea states, a wave inversion method is proposed for a multifrequency HF radar. In this method, the nondirectional wave spectrum is directly retrieved from the radar echoes collected at various frequencies (up to four), and then, the significant wave height and the mean wave period are obtained from the integration of the derived nondirectional wave spectrum. Simulation analysis is carried out to evaluate the performance of the proposed method for a case in four various radar frequencies. Then, the proposed method is applied to a three-day observation to validate its advantages by comparing the radar-estimated and WaveRider-measured nondirectional wave spectra. In addition, a 14-day dataset collected with an HF radar operating at 8.267 and 19.2 MHz during a super Typhoon event is selected for further validation via comparisons between the radar-estimated and the buoy-measured wave parameters. The results indicate that the agreement between them is reasonable, and the comparisons also demonstrate that the accuracy of the wave measurement using the proposed multifrequency method is better than that with a single frequency.