Small Array Airborne Sound Orientation, Passive

This thesis made a research of theory and technology of sources orientation which were tracked by small acoustic arrays.Radar systems are limited in detection and orientation of low flying targets in the air, so technology research of acoustic array orientation of the sources will play more and more important roles in the war field in the future. How to obtain information about sources position and distinguish them accurately are the main contents in this thesis.A research of theory and technology of sources detection and orientation is made in this thesis. In the research, sources are tracked by small acoustic arrays. Theory about orientation of acoustic signals with small arrays is studied and modeled in geometry and mathematics. Furthermore, how to distinguish sound waves arrived in different directions is another important problem.Propagation rules of near ground sources are analyzed carefully, consist of several influent factors: propagation attenuation, reflection on the ground, temperature grads and atmosphere overfall, etc. Based on propagation rules of plane waves, geometry model was set up. Then we can educe mathematic expression as the theory bases applied in later simulation experiments.Estimation of DOA of a single signal is studied thoroughly. Because the principle based on time-delay between two elements traveled in their own direction is adopted. For the two elements, one is the preference element and the other is the element we considered. Precision of DOA estimated in this ways has great relevance to time-delay estimation. Two methods which are applied in estimation of time-delay between elements are introduced and analyzed by simulation experiments. The methods include generalized correlation method and LMS adaptive method. In adaptive method, recursive process is required, so its real-time capability is badly and hardware requirements are high. Real-time capability is necessary and generalized correlation method is emphasized and used mainly. In the process of DOA estimation, proper disposal before and behind experiments should be considered if the results are not very good. At last, errors produced by time-delay estimation and elements position are analyzed.Estimation of multiple signals' DOAs and division of them arrived in different directions are studied. Three algorithms belong to beam-space and element-space are employed in simulation experiments respectively. At first, fundamental theory on one of element-space algorithms—ICSM was presented and the results produced by ICSM are better than that of single frequency method via simulation experiments and factors which affect orientation accuracy and resolving power. Then, for another element-space algorithm—CSM, how to construct and compute focusing matrices is emphasized. Whether focusing matrix is good or not has great effect on theestimated results. At last, beam-space algorithm—BSCSM is stressed and studied thoroughly. The results which were produced by arrays that consist of different elements and different size are compared and analyzed. For different practical signals, how to choose frequencies and band-width and how different size array affect estimated results are analyzed carefully. In order to obtain good results, we choose proper frequency range in terms of practical signals' frequency spectrum. Comparing three methods performance, simulation experiments in which three methods mentioned above are employed respectively are made in same condition. From the simulation results we can see clearly that performance of beam-space method is better than those of element-space.