| The research on radar target echo properties has aroused great attention among researchers due to the development of modern signal processing and high resolution radar techniques in recent years. Especially, most researchers focus on making use of the information obtained from the radar target echo data, such as scattering centers'locations, types, amplitudes, and polarization to judge the targets'states, characteristics and classes. The thesis studies several key problems of radar target scattering centers extraction and its application based on the geometrical theory of diffraction (GTD) model in optical region. The main works are summarized as follows:1 1D scattering centers parameters estimation of radar target based on GTD model In order to increase accuracy and efficiency of the parameters extraction based on 1D GTD model, two improved algorithms are studied in the thesis. The two methods are summarized as follows:(1) The improved total least squares-rotational invariance technique (TLS-ESPRIT) combined with the orthogonality of signal and noise subspace is applied to extract the scattering center based on 1D-GTD model efficiently. Where, the orthogonality of signal and noise subspace is used to determine the scattering center's type. In this way the dense points'types can be judged more accurately. Simulations demonstrate that the improved TLS-ESPRIT combined with the orthogonality method can achieve good accuracy by comparing the results of different conditions, such as signal to noise ratio(SNR), radar bandwidth and the density of scattering centers, on the estimation of parameters.(2) MUSIC algorithm based on Propagator Method (PM-MUSIC) is applied to estimate the scattering center. The PM method instead of the matrix EVD of the MUSIC is applied to compute the noise subspace matrix. Simulations show that the PM-MUSIC can achieve good accuracy in the estimation of scattering centers and reduced the computation complexity under high SNR.2 Multidimensional scattering centers parameters estimation of radar target based on GTD model Multidimensional scattering center extraction can provide more valuable information than 1D scattering center. The thesis makes a further research based on the previous scattering center extraction methods as follows:(1) The 2D-GTD model based on the geometrical theory of diffraction is analyzed, formulated, and approximated to the 2D spectrum estimation model. Simultaneously, the relationship between 3D-GTD model and 3D spectrum estimation model is also derived. (2) 2D modified matrix enhancement and matrix pencil method (2D-MMEMP) and 2D rotational invariance techniques (2D-ESPRIT) are employed to extract the scattering center based on 2D-GTD model. The permutation matrix is used to reduce the calculation cost of the second dimension parameters in the modified methods. Meanwhile, EVD on autocorrelation matrix of enhanced matrix is introduced to decrease the computational load of SVD on enhanced matrix. According to 1D estimated parameters, the proper procedure is selected to estimate the 2D parameters in the 2D-MMEMP method. And in the 2D-ESPRIT method, an adjustable parameter is used to avoid the problem of non-unique eigenvectors caused by the repeated eigenvalues. These two modified methods can achieve good accuracy in the estimation of 2D-scattering centers and avoid the extra pairing procedure。(3) A 3D-MMEMP is developed. The method and 3D-MESPRIT methods are applied to extract the 3D scattering centers based on 3D-GTD model. In these two methods, the permutation matrix is established by utilizing the relationship of three scanning orders on space smoothing. The computational load of the other dimension parameters estimation is decreased. The 3D-MMEMP and 3D-MESPRIT methods do not require any pairing algorithm. Furthermore, they can extract the other dimensions'scattering centers accurately even if there are repeated or similar values in one dimension.3 Full-Polarization scattering centers estimation based on GTD model The thesis studies the 1D and 2D full-polarization scattering center extraction techniques based on full-polarization GTD model by combining the high-resolution technique with the full-polarization information.(1) A polarization linear transform in full-polarization scattering centers estimation is proposed. This new method avoids the parameters extraction of each channel and decreases the computational complexity in smoothing process of PP-MUSIC method. Moreover, the polarization linear transform combined with the eigenspace spatial spectrum estimation method (PL-ES) is introduced to extract the 1D-GTD scattering centers to get better estimation result.(2) A 2D-ESPRIT based on polarization linear transform (2D-PL-ESPRIT) is proposed, which is used to extract the full-polarization 2D-GTD scattering centers. This method avoids the inaccuracy of the signal channel extraction, and also avoids the great computational load of the parallel polarization MUSIC method (PP-MUSIC). Simulations show that the 2D-PL-ESPRIT can achieve good accuracy in the estimation of full-polarization 2D-GTD scattering centers and reduce the computation complexity.4 Radar target identification based on scattering centers extraction Five kinds of fighters scattering centers are used as features in target identification. The performance analyses show the feasibility of the scattering centers as the features to identify the target. The works are detailed as follows: (1) The PM-MUSIC combined with the support vector machine (SVM) is applied to target identification. The 1D scattering centers of five planes are extracted by the PM-MUSIC method, and the spurious scattering centers are excluded by using the range window around the target region. The scale training samples and testing samples are obtained according to the central moments of the distribution of 1-D scattering centers on the target. Finally, targets are identified by SVM.(2) The echo data of five fighters(F16,J6,M2000,Su27 and J8II) are calculated by the radar target back scattering simulation software which is developed by radar target character research center of Nan Jing University of Aeronautics and Astronautics. The 1D scattering centers of five fighters are extracted by the five methods-MUSIC, PM-MUSIC, improved TLS-ESPRIT, IFFT and Matrix pencil (MP) under different conditions(SNR, bandwidth, data compression ratio). And the five fighters are identified by the two kinds of identification methods–SVM and adaptive Gaussian classifier (AGC) respectively. Simulations demonstrate that the PM-MUSIC combined with the SVM has a better performance.5 RCS data compression and fitting based on scattering centers extraction This thesis studies the application of scattering centers in RCS data compression based on GTD model. The MP, improved TLS-ESPRIT and MUSIC methods are applied to extract the scattering centers parameters. Then the extracted scattering centers are used to fit and reconstruct the RCS data by the GTD model. In this way, the echo data are compressed.(1) The IFFT method and scattering extraction method based on GTD model, such as MP, improved TLS-ESPRIT and MUSIC, are used to extract the scattering centers for echo data compression.(2) The thesis compares the RCS fitting performance of several compression methods, discuses the fitting effect of the point target and volume target. The fitting performance of frequency domain and angle domain is analyzed, and the fitting performance in different azimuth is analyzed also. Simulations show a good application effect of the scattering center technique in RCS data compression and fitting field.
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