Research On Method For Ocean Surface Currents Measurement With Single Station Hf Hybrid Sky-surface Wave Radar

High frequency hybrid sky-surface wave radar(or HFHSSWR for short)is an important detection tool of sea state,which can inverse important information on wind,waves and currents utilizing the radar echo,then it has the ability to monitor sea state with high precision in a large area and any weather.Due to the complex radio propagation channel,the characteristics of frequency shift and broadening of first-order sea clutter for High frequency hybrid sky-surface wave radar make it is harder to isolate the first-order sea clutter spectrum than that of high frequency surface wave radar.And currents measured by single radar station are radial currents along radar radiation direction,generally,vector ocean currents are obtained from vector synthesis by radial flow observed by two or more radars stations.But sometimes two radars cannot be configured or running limited by natural conditions,capital,communication and other factors.In order to solve these problems,provide the total currents based on radials from single site radar and assess detection accuracy,this paper makes a research on methods for ocean surface currents measurement with single station HF hybrid sky-surface wave radar system.Main work of this paper is as follows:(1)It was founded that the first-order sea clutter spectrum continuously distributed on the two-dimensional range-Doppler spectrum.Then a two-dimensional signal-to-noise ratio method was proposed to isolate the first-order sea clutter spectrum for HFHSSWR.From the quantitative analysis of frequency shift and broadening of the first-order clutter spectrum caused by bistatic angle,ionospheric conditions and ocean currents,the determining method and the value ranges of three parameters were given,which are the center location,the width of first-order sea clutter spectrum and the spacing of the two first-order sea clutter.Finally the proposed method were applied to simulated and measured data to verify its validity.(2)In order to provide the total currents based on radials from single station radar,some single station vector current synthesis methods have been developed,in which the stream function method(SFM)and another method based on least-squares fitting(LSF)are two typical methods.To evaluate the accuracy and the scope of application of the two methods and determine the optimal synthesis algorithm to obtain vector currents under different single station conditions,this paper carried out evaluation and analysis of the two methods.Firstly,the performance of SFM and LSF are evaluated with simulated radial data.It was found that both of the two methods are nearly equivalent in the condition of uniform currents,while SFM has advantages over LSF both in error acceptance and robustness when ocean surface current field has spatial variation in current velocity.Then the two methods are applied to the experiment data of HFSWR,the results showed that the RMS difference of SFM results is smaller than that of LSF results compared with current meter observations.(3)In order to verify and assess the performance of HFHSSWR system to detect elements of the marine environment,verification test of HFHSSWR system against in situ measurements had been accomplished on May 16~20,2014,in the Yellow Sea,which gained a rich supply of data about ocean surface currents,waves,wind and other elements of the marine environment.current velocity and azimuth can be obtained by applying the digital beam forming technology(DBF)and instantaneous frequency method(IF),then the paper presents comparison results of surface currents measurements.The results indicate the HFHSSWR system is meet the need of design.Finally we obtain the single radar station vector flow field.