| High frequency surface wave radar(HFSWR),whose operating frequency is3-30 MHz,takes advantage of the characteristic of low attenuation of vertically polarized electromagnetic wave propagation over the sea surface,which can provide a real-time,all-weather,large-area surveillance to sea surface far beyond the horizon.The radar system is low-cost and easy to maintain,which has been an important approach to realize three dimensional monitoring of ocean environment.Compared with land-based HFSWR,shipborne HFSWR can exploit its maneuverability and agility to increase the survivability and to extend the detection range in the complex oceans environment,which has been the deployment trend in the future.It has an extensive application value and an important research significance not only for marine moving targe detection for military aim but also for ocean dynamic parameter inversion in civil field.HFSWR can measure ocean dynamic parameters effectively by exploiting the first-and second-order scattering mechanism of high frequency electromagnetic wave on rough sea surface.At present,the theoretical system and the application technology of land-based HFSWR in the field of ocean remote sensing has been relatively mature.Different types of HFSWR systems have been successfully developed at home and abroad,which have been widely used in marine environmental monitoring.However,the research of shipborne HFSWR in the field of ocean remote sensing is just in the beginning.The theoretical system is still not mature and the application technology needs to be further developed.Based on the electromagnetic scattering theory of rough sea surface,this paper will implement the research on ocean surface electromagnetic scattering modeling and the inversion methos of wind and wave paramenters based on shipborne HFSWR.The research results in this paper improve the theoretical system of ocean remote sensing of shipborne HFSWR and provide theoretical foundation and technical support for the application of shipborne HFSWR in marine monitoring in China.The main research contents are as following:(1)Based on the electromagnetic scattering theory of rough sea surface,the first-and second-order ocean surface electromagnetic scattering cross sections for the monostatic and bistatic floating-based HFSWR incorporating a multi-frequency six degree-of-freedom oscillation motion model are derived.Firstly,the mathematical model of a six degree-of-freedom oscillation motion of the floating platform is built.Then,the first-and second-order ocean surface electromagnetic scattering cross sections for the monostatic floating-based HFSWR incorporating a single-frequency six degree-of-freedom oscillation motion model are derived.The derived results can be further extended to the monostatic and bistatic cases incorporating a multi-frequency six degree-of-freedom oscillation motion model.Furthermore,the effect of six degree-of-freedom oscillation motion on the derived results,the similarities and differences of the monostatic and bistatic cases,and the effect of the bistatic angle are analyzed in detail by computer simulation.Finally,the derived results are preliminarily verified by the measured radar data.The derivation and analysis in this part lay a theoretical foundation for the derivation of the firstand second-order ocean surface electromagnetic scattering cross sections of shipborne HFSWR and the application of oceans remote sensing of the floating-based HFSWR in the future.(2)Based on the research mentioned above,the first-and second-order ocean surface electromagnetic scattering cross sections for shipborne HFSWR incorporating a multi-frequency six degree-of-freedom oscillation motion model are derived.Firstly,the mathematical model of a six degree-of-freedom oscillation motion of the shipborne platform is built.Then,based on the sea surface electromagnetic scattering theory of the floating-based HFSWR,the first-and second-order ocean surface electromagnetic scattering cross sections for the shipborne HFSWR incorporating uniform linear motion and a single-frequency six degree-of-freedom oscillation motion model are derived.The derived results can be further extended to the multi-frequency cases.Furthermore,the effect of uniform linear motion and six degree-of-freedom oscillation motion on the derived results is analyzed in detail by computer simulation.Finally,the spreading phenomenon of the first-order Bragg peak is preliminarily verified by the measured radar data.The derivation and analysis in this part establish a theoretical foundation for ocean dynamics parameter inversion with shipborne HFSWR.(3)In order to solve the problem of the small deck space of the shipborne platform,a method of extracting ocean surface wind direction using shipborne HFSWR with a single antenna is proposed.Firstly,the first-order Doppler spreading spectrum model of Shipborne HFSWR is analyzed theoretically.Then,when wave spreading factor is a empirical value,the mathematical model of ocean surface wind direction inversion is developed by the ratio of the positive and negative first-order Bragg peak energies.Based on the spreading characteristic of the first-order radar Doppler spectrum,a method of extracting ocean surface wind direction using shipborne HFSWR with a single antenna is proposed and the problem of the wind direction ambiguity is solved using the minimun difference method.Finally,the feasibility and validity of the proposed method are verified by computer simulation and the experimental results of shipborne HFSWR.(4)Based on the relationship among wave spreading parameter,wind direction and wind speed,an approach for simultaneously extracting the unambiguous ocean surface wind direction and wind speed using shipborne HFSWR with a single antenna is proposed.Firstly,the mathematical model of ocean surface wind direction versus a variable wave spreading parameter is developed.Then,based on the spreading characteristic of the first-order radar Doppler spectrum,an approach for simultaneously extracting the unambiguous ocean surface wind direction and the unique wave spreading parameter using shipborne HFSWR with a single antenna is proposed.Furthermore,the relationship between ocean surface wind speed and the wave spreading parameter is derived on the basis of the relationship between the drag coefficient and the wave spreading parameter,and then the wind speed can be determined by the determined wave spreading parameter.Moreover,the effects of covered region shift,real sailing conditions and external Gaussian noise on the proposed method have been analyzed by computer simultion.Finally,experimental results measured by shipborne HFSWR validate the presented method and evaluate the detection accuracy and distance limit.The measured ocean surface wind speed in this part provides the data support for subsequent significant wave height inversion using shipborne HFSWR.(5)Based on the mathematical model between wind speed and significant wave height,an approach for extracting ocean surface significant wave height using shipborne HFSWR with a single antenna is proposed.Firstly,based on physical oceanography theory,the mathematical model of ocean surface significant wave height and non-directional wave spectrum is introduced and the corresponding relationship between ocean surface significant wave height and wind speed is developed.Furthermore,by optimizing ocean surface wind speed data measured before,ocean surface significant wave height can be extracted by using the first-order Doppler spectrum of shipborne HFSWR.Finally,the vaildity of the proposed method is verified by the experimental results measured by shipborne HFSWR when waves are fully developed. |
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