Research On Wave Echo Extraction And High Frequency Ground Wave Radar Sea-state Parameters Inversion Method

High-frequency electromagnetic wave(3-30MHz)can be used to spread around the coastal surface.High-frequency ground wave radar can detect moving targets such as ships and low-altitude aircraft beyond the horizon.It can also monitor some ocean dynamic parameters such as sea surface wind,wave and current.Since the 1970 s,high frequency ground wave radar has developed rapidly,especially in marine environment monitoring.In this paper,the extraction of HF ground wave radar ocean echo and the inversion algorithm of wind,wave and flow field parameters are studied,and a set of inversion algorithm of sea state parameters suitable for HF ground wave radar is formed.Firstly,this paper studies the method of separating the first-order and second-order spectral regions of ocean echoes.For the first time,the matched peak method is proposed to detect the location of the first-order Bragg peak.The algorithm is verified by the measured data.It is found that the method has good detection effect and is easy to implement,and is suitable for the detection of the first-order Bragg peak.After that,the boundary of the first-order echo spectrum region is extracted,and the results are analyzed using the measured data,which proves the effectiveness of the first-order echo spectrum extraction method.After extracting the first-order spectral region,the extraction method of the second-order echo spectrum is given.The experimental data prove that the detection effect is good and the feasibility is high,which provides conditions for the follow-up wave height and wind speed inversion.After the extraction of ocean echoes,the inversion algorithms of wind field,wave field and flow field parameters are deeply studied in this paper.In the aspect of wave field,the classical inversion algorithms of wave spectrum,wave period and wave height are analyzed firstly.Then,in the aspect of wave height inversion,the measured data analysis results of wave height inversion using various classical algorithms are given.Finally,the parameters of the classical methods are adjusted to make it a wave parameter inversion algorithm suitable for the detection of sea area by this radar system.On the problem of wind direction parameter extraction,a multi-beam fitting angle method is proposed to eliminate the ambiguity of wind direction.By calculating the variation trend of the angle between the wind direction and the adjacent multiple beams,the real wind direction can be obtained.The analysis results of the measured data show that the multi-beam fitting angle method has good consistency and high precision in wind direction retrieval,and can be used as a method for radar system to retrieve wind direction.The SMB method,the peak frequency method and the effective wave height method are introduced in detail in wind speed inversion.By comparing the inversion results of measured data with the prediction information,it is proved that the three methods can better retrieve wind speed information,among which the peak frequency method has the lowest complexity.In the field of flow field,the results of radial velocity inversion are optimized firstly,and then an improved flow function model is proposed to invert the vector flow field.A more suitable model for the inversion of the vector flow field is obtained.The results of the measured data verify that the inversion results of the radial flow field and the vector flow field are in good agreement with the predicted values.