Studies On Time-Frequency Analysis And Target Recognition With Polarimetric Radar

With the development of the theory and technology of wide-band signal, and the improvement of polarimetric technology, the radar having ability to get high resolution range profiles and fulfill full polarization measurement or polarization shifting, is becoming the mainstream of modern radars, which improves and extends the detection capability and application domain of radar. Compared with the trend of wide-band and high range resolution in radar technology, the classical polarization theory, which is suitable in narrow-band and low range resolution case, shows its imperfectness and deficiency. The foundation of the theory system of instantaneous polarizaiton(InPol) provides powerful theoretical tools for the representation of electromagnetic(EM) wave's polarization and description of radar target's wide-band polarization scattering characteristic. So it is greatly beneficial to the exploitaion of radar target's polarization scattering imformation and the improvement of wide-band polarimetric radar's detection performance.In this thesis, with the guidance of InPol theory system, the elementary methods of EM wave's InPol time-frequency analysis are presented, which are extension and evolution of the concept of EM wave's instantaneous polarization and provide powerful theoretical tools for the representation and analysis of time-varying EM wave's InPol properties in time-frequency domain. With these methods, the InPol properties of wide-band polarimetric radar target's scattering waves are described and analyzed in time-frequency domain, and two effective target recoginition methods are proposed.The work of this thesis includes research both in theory and in application:In theory, it firstly elucidates the necessity and physical meaning of InPol time-frequency analysis(InPol TFA) of time-varying EM waves, and presents the basic property requirements of InPol time-frequency distribution(InPol TFD). Then, some elementary InPol time-frequency transforms, such as InPol short-time Fourier transform(InPol STFT), InPol Wigner-Ville distribution(InPol WVD), InPol ambiguity function, Cohen's class InPol time-frequency distribution, and InPol pseudo WVD(InPol PWD), are introduced, and their properties are discussed. The difference and relationship between InPol TFA method and conventional TFA method are also compared. These concepts and methods compose the basic framework of EM wave InPol TFA, which lays theoretical foundation for the following target recognition research.In application, two wide-band polarimetric radar target recognition methods are proposed. The one is based on InPol WVD correaltion, which can utilize the InPol information of target's return well. The relationship between the improvement of this method's performance and target scattering wave's polarization divergence are demostrated too. The other is based on features formed by singular values of target return's InPol TFD, and selects BP network as target classifier. Recognition results show that the method based on InPol TFD has better performance than the method based on conventional TFD.The studies on TFA and target recognition with polarimetric radar in this thesis indicate that with EM wave InPol TFA method, both the energy and the polarization state distribution in time-frequency domain are described for a time-varying EM wave. That is to say, the characteristic description and information exploitaion of a time-varying EM wave are more complete and comprehensive when using this technology. It is proved that wide-band polarimetric target recognition methods based on InPol TFA can achieve higher correct recognition rates and better antmoise performance than the methods based on conventional TFA.