Distributed Target Modeling And High Resolution DOA Estimation

Target modeling is necessary for detecting they characteristics. When a target is detected, it is essential to explore the signals reflected form the target according to its model by using some analyzing methods. Thereby target classification, target recognition and parameter estimation can be realized based on the characteristics of target echoes. Therefore, it makes a difference for the accuracy of result when the model is well established or not. Distributed target modeling is paid more attraction in recent years. It involves the shapes, sizes, and structures of targets, which represents the geometric characteristics of targets accurately. It is more preferable than traditional point model to estimate the precise structures of large size targets and satisfy the requirement of modern weapon equipment to recognize targets and attack the vital parts of targets. In this paper, the modeling and high-resolution direction- finding for distributed targets are focused on, which are divided as follows. 1. Highlight scattering characteristics of distributed targets is described synthetically. Aiming at highlight models, the methods to determine model parameters of several geometric objects are introduced. Based on highlight models, specular reflection echoes of sound pulse from submarine are simulated. Highlight echoes for every incident angle are discussed and the relationship between highlight echo composition and incident angle is clarified. 2. Several methods to analyze echoes suitable for continuously scattering targets are introduced systematically, which include the Helmholtz integral equation approximate method (LIIEAM), the Fresnel semi-waveband approximate method (FSAM), the boundary element method (BEM), the distributed source boundary point method (DSBPM) and the time domain integral equation method (TDLEM). Focusing on the characteristics of continuously scattering targets, and combining with the requirements of applications, the method to construct mesh structure of target surface is presented. According to the mesh model, the acoustic radiation from a target is simulated by using general BEM and DSBPM. Based on the results, the contrast between the performances of the two methods is carried out, which indicates the superiority of DSBPM, especially at the resonance frequencies of targets. 3. Based on the structure and scattering characteristics of a submarine, its mesh model is presented. According to the model, the echoes from submarine for every incident angle are simulated by using HLEAM and TDIEM. By analysis, contrast and discussion of echoes, it is proved that the echoes from submarine can be described by using the theory of geometric highlights and the echoes from targets based on continuously scattering model have highlight characteristics. Therefore, direction of arrival (DOA) estimation for a distributed target can be reduced to finding the directions of its highlights in many applications. 4. Based on the coherence of highlight echoes, two types of methods to estimate the source number are presented, including the joint estimate method utilizing information theoretical criteria(ITC) and the matrix decomposition method. According to the mesh model, the number of submarine highlights is estimated for every incident angle by using the joint estimate method. The results obey the theory of submarine highlights structure, which proves that DOA estimation for a distributed target can be carried out reasonably via finding the directions of its highlights. 5. Aiming a...