Research And Application Of Multi-frequency HF Ground Wave Radar Sea State Inversion Technology

HF(High-Frequency) ground wave radar ocean environment monitoring technology is a rapidly developing ocean remote sensing technology. It uses wave diffraction propagation characteristics of the high-frequency vertical polarized electromagnetic that when it is radiated in the coastal water surface, there is less energy attenuation. When high-frequency signal with high-power are radiated onto the sea, the two kind of waves will produce the strongest backscatter which run point to or away from the radar with their wavelength equal to1/2radar wavelength. The scattering of waves on the radar beam is similar to the X-ray incident to the lattice caused Bragg resonant scattering, so it is known as Bragg scattering or first-order scattering. The state of the sea surface and its variation is reflected in the echo Doppler spectrum, so it is possible to use Barrick’s first-order and second-order scattering cross section equation to analyze the Doppler spectrum and invert ocean dynamics parameters, such as wind, waves and currents. HF ground wave radar for monitoring the sea surface environment has lots of advantages including large coverage, high detection accuracy, low operating costs, real-time, all-weather working. And it is considered one of the most ideal ocean environmental monitoring equipments for its ability of monitoring the sea outside the sight.Compared with the traditional single-frequency HF radar, anti-jamming capability and self-correction capability of multi-frequency HF ground wave radar are significantly enhanced, and ocean dynamics information which contains in echo is greatly increased. In terms of currents inversion, it can get a variety of scales and different depths of the ocean current results. In the wind field, multi-frequency sea echo can be used to extract wind speed and direction information with high accuracy. For wave detection, the use of multi-frequency radar can choose the optimal operating frequency to get a more accurate result of wave height and wave period. The development of HF ground wave radar system, which can be multi-frequency time work, is the main development trends of high-frequency ground wave radar. At the same time, the study of multi-frequency HF ground wave radar sea-state inversion theory, development of a real-time multi-frequency sea-state parameter inversion method are the main research directions in the field of ocean environmental monitoring of high-frequency ground wave radar.In support of "Eleventh Five-Year" National863Program project-"New Multi-Function HF Ground Wave Radar", a Multi-frequency HF ground wave radar, which can work with a small antenna array is developed by our team. The aim of this paper closely combines with this project and is to study the sea state parameter inversion theory of Multi-frequency HF ground wave radar and the method of multi-frequency data fusion. And give full play to the advantages of Multi-frequency HF ground wave radar, such as more operating frequencies, richer echoes. To improve the practicality and reliability of radar sea state parameters inversion algorithm and obtain a stable and accurate wave, wind, current information is the aim of this paper. The algorithm is applied to Multi-frequency HF ground wave radar system.According to the research objectives, this paper focuses on sea state parameter inversion theory and methods of Multi-frequency HF ground wave radar. The field of high-frequency radar scattering mechanism, estimation of sea echo Doppler spectrum, wave, wind and surface current parameter inversion algorithm, as well as multi-frequency data fusion algorithm has been carried out extensive and in-depth research. On the basis of summing up and improving optimizing and innovating the domestic and foreign scholars’ outstanding research, this paper proposes a Multi-frequency HF ground wave radar sea-state inversion algorithm.Firstly, this paper studies the basic theory of HF radar ocean remote sensing, especially the first and second order scattering mechanisms of HF electromagnetic waves and rough sea surface. And the numerical simulation of high-frequency radar echo spectrum is completed. This paper analyzes and discusses the advantages of Multi-frequency HF ground wave radar for monitoring the ocean environment. By studying the mechanism of electromagnetic wave scattering, first and second order radar equation, and the numerical simulation results, this paper analysis the key problem of sea state parameter inversion using Multi-frequency HF ground wave radar. It means how to improve the accuracy of Multi-frequency HF radar sea state parameters inversion.According to the key issues of Multi-frequency HF radar sea state parameters inversion, we have studied the basic theory of power spectral and spatial spectrum estimation. Considering the characteristics of Multi-frequency HF ground wave radar system, this paper points out the most suitable for Multi-frequency HF ground wave radar spectral estimation methods, and this laid a solid foundation for the accurate inversion of the sea state parameters.This paper presents a thorough study of the basic theories and methods of waves, winds and currents parameter inversion using Multi-frequency HF ground wave radar:1) Wave parameters inversion:this paper summarizes the most commonly used wave height, mean period and wave spectra inversion method. Based on a detailed comparison and analysis of a lot of inversion algorithms, this paper points out a variety of advantages and disadvantages of each method. For Multi-frequency HF ground wave radar wave height inversion method, the minimum variance method is adopted to fit the measurements of Multi-frequency HF ground wave radar and wave buoy, and gets the inversion parameters of every operating frequencies of Multi-frequency HF ground wave radar.2) Wind parameter inversion. this paper studies several mature wind speed and wind direction inversion method of HF radar all over the world and analyzes the characteristics of each method. By theoretical analysis, the basic conditions of the wind inversion algorithm, the relationship between radar operating frequency and the minimum wind speed of the sea surface, is obtained. By analyzing the key point in wind speed and direction inversion process, comparing the simulated and measured results, the wind speed and direction inversion method, which is fit for Multi-frequency HF ground wave radar is obtained.3) Currents parameter inversion. This paper carries some researches of the basic method to extract currents by HF ground wave radar. Focusing on the key issues of current extraction algorithm, the azimuth estimation algorithm is discussed, and the detailed descriptions of the surface current based on MUSIC algorithm are presented in this paper.4) This paper detailedly describes HF ground wave radar sea state inversion process, especially focus on the key modules in the process of data preprocessing, including:two FFT operations, sea echo spectrum estimation, anti-jamming processing, first-order spectrum and second-order spectrum separation.5) This paper presents the data fusion method of multi-frequency HF ground wave radar waves, wind, currents inversion results. And it mainly focuses on data fusion algorithm of multi-frequency wave height measurements.Finally, this paper presents a contrast verification of Multi-frequency HF ground wave radar waves, wind speed, wind direction and radial current measurement with ADCP and wave buoy observations. And then this paper points out the causes of radar measurement error. The results show that the Multi-frequency HF ground wave radar has a good performance of sea state parameters inversion.