Theory And Technology On Reconstructing 3D Scattering Centers Of Radar Targets In Optical Region

Scattering center model describes the scattering characteristic of radar targets in optical region. Reconstructing credible three dimensional (3D) scattering center model of radar targets from multiple one dimensional (1D) range profiles by advanced signal processing methods not only leads to a deeper insight into the scattering mechanism at high frequency, but also facilitates building target signature database and realizing automatic radar target recognition. This dissertation focuses on reconstructing 3D scattering center model of radar targets in optical region based on 1D measurements at multiple viewing angles. Three problems are studied: estimating 1D scattering center parameters with high accuracy; reconstructing 3D positions of the scattering centers for non-cooperative targets and reconstructing complete 3D scattering center model under controllable measuring conditions. More details are arranged as follows.Chapter 2 focuses on the estimation of 1D scattering center parameters with high accuracy. Firstly the performance bounds (Cramér-Rao Bound, CRB) on the 1D scattering center parameter estimates are deduced together with their relation with the radar system parameters. The resolving ability of wideband radar and the SNR threshold for discriminating scatterer's type are further deduced. Two algorithms, one based on the structured subspace decomposition method and the other based on the matrix pencil method, are designed to process measured data with complementary performance in computing complexity and estimating precision.Chapter 3 studies the theory and methodology of reconstructing 3D position of scattering centers in non-cooperative situation. The CRB of the reconstruction model is deduced, where the singular Fisher information matrix caused by the parameter constraints and the rotary equivalence in solutions is specially treated. This work provides both a benchmark for evaluating different reconstructing algorithms and an approach to predict the reconstructing precision of different configurations. A novel reconstructing algorithm based on the signal subspace invariance (SSI) is proposed, which outperforms previous algorithms based on the geometric invariance (GI) in both computing complexity and reconstructing precision. An example of reconstructing the scattering centers of an airplane is given to verify the feasibility of this method.Chapter 4 focuses on reconstructing the complete 3D scattering center model under controllable measuring/EM computing conditions. A feasible reconstructing scheme within existing measuring/EM computing ability is proposed, which exploits the regulation of 1D projection positions and the stability of scattering coefficients of stable scattering centers. We use several signal processing methods such as the Hough transform, binary morphology operates, etc., to break the bottlenecks in designing the reconstructing scheme. The 3D scattering center models of three complex targets are reconstructed using this scheme. The density of viewing angles required in this scheme is much sparser than in synthetic aperture radar imaging, which greatly cuts down the original data needed for model reconstruction. The reconstructed model contains most of the stable scattering centers of complex targets and is adaptable at extrapolated frequencies and interpolated viewing angles. All sorts of target signatures such as RCS, radar images from 1D to 3D can be recovered from this model.Finally, a systematic conclusion and some discussions on further work are presented.