Research On High Frequency Ground Wave Radar Sea-State Parameters Inversion Method

As a new kind of ocean remote sensing technology, high frequency ground wave radar(HFGWR) ocean environment monitoring technology has developed rapidly since the 1970 s. The electromagnetic wave emitted by the radar interacts with the rough sea surface, and the first-order scattering and second-order scattering will generate different amplitude peaks in the radar sea surface echo spectrum. So there is a way to invert ocean dynamics parameters, such as wind, waves and currents by using Barrick’s first-order and second-order radar spectral cross section equation to analyze the echo Doppler spectrum. With its advantages of long detection range, real-time, not influenced by adverse weather, HFGWR ocean environment monitoring technology has become one of the most important means of ocean remote sensing.In recent years, the technology of currents detection has matured and entered industrial stage, whereas the technology of wind and wave is still in the phase of research. In the support of a large national defense project, this paper studies sea-state parameters inversion from HFGWR, wind, wave and currents are included. And it proposes an inversion algorithm which is applicable for the radar system of the project in the end.Firstly, the basic theory of sea-state parameter inversion of HFGWR is studied, especially the scattering mechanism of HFGWR and rough sea surface. The HFGWR sea echo spectrum is simulated and the basic conditions for parameter inversion.is pointed out by changing the parameters to observe the characteristic of the echo spectrum.Then, this paper carried out research on the inversion algorithm of wind, wave and currents. In the wave field, several conventional and international methods of ocean wave spectra and wave height are described. On the basis of theoretical analysis and simulation of every method, and the application range of the algorithm and its advantages and disadvantages, a wave field inversion algorithm with high accuracy is obtained. The wind field is comprised with two parts, wind direction inversion and wind speed inversion. The core problem of wind direction inversion is to eliminate the ambiguity of wind direction. This paper uses the improved multi beam least square method to retrieve wind direction. The algorithm assumes that the wind direction of adjacent sea elements is the same or almost unchanged. For wind speed inversion, this paper studies several mature and classic methods. And an algorithm suitable for the radar system of the project is obtained by considering the performance and accuracy of the algorithm. In the field of currents, the extraction principle of ocean current radial velocity is analyzed, and a new method of first-order sea clutter extraction is proposed. This method uses the least square approximation to obtain the approximation function of the echo Doppler spectrum. And the spectrum around Bragg peak is smoothed. As a consequence, the influence which is brought by the spectrum splitting which is caused by high coherent accumulation time and high frequency noise will be reduced. The proposed method can effectively solve the problem that the recognized Bragg peak position is not accurate, and directly improve the accuracy of the extraction of the current radial velocity and the wind direction.