Study On Some Problems In Ocean Environment Remote Sensing Based On Bistatic Hf Ground Wave Radar

HFGWR (High Frequency Ground Wave Radar),developed in the1980’s,is a kind of equipment which can continuously monitor large ocean dyamics environment. To achieve larger-scale ocean dynamics environmental collaborative monitoring, radar netting based on multistatic HFGWRs becomes a urgent problem to be studied in ocean environmental monitoring technology. It is also a hot research in the development and application of HFGWR.Combining with National863High-Tech Project of China undertaken by the Radio Wave Propagation Laboratory in Wuhan University, this thesis discusses some problems in ocean environment remote sensing based on bistatic HFGWR model,such as the basic non-backscattering theory of multistatic HFGWRs netting detection, numerical simulation of non-backscattering echo, inversion method of dynamic parameters and radar netting engineering etc.. The main contents of thesis are as follow:1. Approximating the sea as a perfectly conducting surface, the first-and second-order bistatic incoherent scattering coefficents of sea surface in the case of infinitely deep water, narrow band antenna and VV polarization HF wave are derived based on the perturbation method, the non-backscattering Bragg mechanism is analyzed, and the basic theory of ocean environment remote sensing based on bistatic HFGWR is formed. Degenerating the bistatic radar to monostatic radar as a special case, the results in this thesis are the same with the results obtained by Barrick in1972. In appendix, the bistatic scattering coefficients of two dimensional static slightly rough surface are derived in detail. The first-and second-order bistatic scattering coefficients of general rough surface and ideal conductive rough surface in the case of HH, VH, W, HV polarization are given and divided into coherent part and incoherent part.2. Choosing the ocean directional spectrum model to be the product of a PM nondirectional spectrum and a cardioid directional factor, the sea echo Doppler spectra of bistatic HFGWR are simulated based on the method of integral along the constant Doppler frequency contours, and the effects of wind direction, wind speed, operating frequency and bistatic angle on bistatic sea echo Doppler spectra are discussed. When the bistatic angle is fixed, the trends of bistatic sea echo spectrum under the influence of wind speed and wind direction are the same with those of monostatic sea echo spectrum. However, the integrable singularities resulting from electromagnetic coupling coefficient and the corresponding secondary peaks of bistatic sea echo spectrum vary with the bistatic angle. And the intensity and frequency distribution range of second-order spectrum decrease with the increasing bistatic angle.3. Taking bistatic HFGWR as the ocean environment remote sensing model, the inversion method of current speed and wind direction based on the first-order sea echo spectrum and the inversion method of wave height and wind speed based on the second-order sea echo spectrum are discussed, the current velocity along a hyperbola is obtained based on MUSIC algorithm from T-Rb bistatic radar simulated data and measured data, the wave height and wind speed are obtained based on Howell algorithm from simulated bistatic sea echo spectrum. Results show that the bistatic radar which consists of one transmitter T and one receiver Rb can only measure the current velocity along a hyperbola and wind direction ambiguity exists too. Howevjer,the T/Rm-Rb system can obtain the current vector velocity and can also be used to obtain the true wind direction. In addition, the applicable condition of Howell’s algorithm is complemented, and the selection principle of the retained number of singular values of the kernel matrix in Howell’s algorithm is determined.4. Taking the application of bistatic HFGWR as the background, some problems on engineering application, such as the bistatic radar detection capability, vector current detection accuracy and radar distribution, etc., are discussed. Results show that, when radar system operates in the bistatic way (that is,0<LB<s(1/2)KB), the longer the baseline and the smaller the bistatic angle, the stronger the detection capability (that is, the bigger the detection range sum). Therefore, the optimal baseline length may be determined by the maximum detection range sum among the design parameters of bistatic radar. When the T/Rm-Rb system is used to extract the vector current, the region near the bistatic receiver Rb as well as the baseline should be avoided and the optimal range of bistatic angle is [25°,70°]. Then, the distribution principle is given when combining the optimal baseline length with the optimal range of bistatic angle.