Sea Surface Wind Field Retrieval Of Compact HF Radar Based On Wind-current Interaction Research

Compact high frequency surface wave radar(HFSWR)is an important remote sensing tool for sea state,which can monitor the dynamic parameters of ocean surface such as surface current,wind field and wave field all day,all weather and over-the-horizon based on the characteristics of vertical polarization electromagnetic wave diffracting along the sea surface.HF radar uses the offset of the first-order Doppler frequency of the ocean echo relative to the Bragg frequency to estimate the ocean surface current.After more than 30 years of research and development,the current measurement method has got high accuracy,and has been widely commercialized.The wind field retrieval of HF radar mainly depends on the fluctuating ocean echo power,which limits the accuracy and range of the measurement results of HF radar(especially in compact system).Therefore,improving the performance of HF radar wind field retrieval has become an important research direction.In fact,the friction force of the wind field on the sea surface causes the wind-driven current,which affects the current.Based on the high reliability of HF radar current measurement,this paper studies the interaction between wind and current,and proposes a wind field inversion algorithm based on wind-driven current.Based on Ekman drift theory and Stokes drift theory,this paper discusses the relationship between wind-driven current and wind,which provides a theoretical basis for retrieving wind parameters based on wind-driven current.Theoretical derivation and numerical simulation show that the velocity of wind-driven current increases with the increase of wind speed,and the relationship between them is related to the total water depth,latitude and the length of dimensionless wind zone.In addition,the angle between the wind-driven current and the wind decreases with the increase of wind speed,and finally stabilizes within 10°.Therefore,it is feasible to retrieve wind field from wind-driven current field extracted by HF radar.Then,the method and steps of extracting wind direction information based on wind-driven current are introduced in detail.Firstly,by analyzing the generation mechanism and characteristics of various components in the current,the extraction method of wind-driven current is introduced,so as to obtain high-precision wind-driven current field.Then,combined with theoretical analysis and actual data,it is found that the angle between the wind-driven current and wind decreases with the increase of wind speed,and finally tends to a stable value.The angle between the wind-driven current and the wind collected by the buoy is calculated,and the method of wind direction inversion based on the angle and the wind-driven current direction is proposed to extract the wind direction field in low and high sea state.Compared with the traditional algorithm,the root mean square error(relative to the numerical model)of the method is smaller in low and high sea conditions.In addition,fuzzy problem of wind direction extraction by ratio method,and the problem of wind direction rotation at the edge of radar illumination do not exist in the method.Among the existing wind speed inversion algorithms of HF radar,SMB method and empirical relation method are only suitable for high sea conditions,while JONSWAP algorithm is only suitable for low sea conditions,and the measurement accuracy of the three algorithms is limited by the performance of wave height inversion.To solve these problems,based on the strong correlation between wind-driven current speed and wind speed,a new wind speed retrieval algorithm of HF radar is proposed,in which neural network is used to map the accurate relationship between the speed of winddriven current and wind.Because of the utilization of current measurement with high accuracy rather than the wave height of HF radar in wind speed retrieval,the method has better measurement accuracy and wider measurement range than the traditional algorithm.The experimental data show that the average correlation coefficient between the retrieved wind speed and the reference wind speed in the detection range of 84 km from radar station is 0.86,the average root mean square error is 2.38 m/s,and the root mean square error at the buoy is about 1 m /s-1.5 m/s lower than the traditional algorithm.Based on the wind-current relationship of the ocean surface,this paper uses the high-precision ocean current retrieved by the compact HF radar to effectively realize the high-precision and large-scale observation of the ocean surface wind field,which provides a new solution for the wind field retrieval of the compact HF radar,and will strongly promote the popularization and application of the compact HF radar.