Research On Direction Finding And Enhancement Method Of Low-elevation-angle Target Based On Differential Microphone Array

For low elevation angle targets such as low altitude helicopters and ground tracked vehicles,passive acoustic detection technology uses acoustic signals emitted by the target moving parts to achieve detection and identification,which can effectively solve the problems of electronic interference and physical obstruction that radar detection faces.In recent years,with the development of micro-electro-mechanical systems(MEMS)technology,microphones have become more miniaturized and intelligent.Miniature sound detection nodes in the form of a microphone array have the characteristics of low cost,simple structure,and low power consumption.Multiple micro sound detection nodes can also be deployed in large numbers by means of scattering,and further establish an acoustic regional alert system through networking.Direction finding and enhancement of low elevation angle target based on a miniature microphone array is an important task when the corresponding system is applied.The related research results have broad application prospects and good practical application values in the military and civilian fields.Aiming at the small-micro-plane differential microphone array,this thesis focuses on the method of direction finding and enhancement of low elevation angle target.Firstly,the law of atmospheric sound propagation and the signal generation mechanism and time-frequency characteristics of low elevation angle target sound are discussed.Through simulation analysis,it is found that the low elevation angle target sound signal does not have good short-term orthogonality and time-frequency sparseness(W-DO)characteristics.Therefore,the existing multiple sound source direction finding methods based on sound intensity estimation for speech signals do not work well on low elevation angle target sound sources.Considering that a single micro sound detection node based on a differential microphone array usually has a weak detection capability and a small monitoring area,this thesis focuses on the detection and direction finding methods of the strongest target sound sources in a short range.Specifically,we detect the target sound source by the short-time energy double-threshold method,and then we propose an improved histogram method based on time-frequency filtering and power weighting to estimate the azimuth of the target.Finally,we distinguish between ground and low-altitude targets through a template matching method.After completing the target direction finding task,an interference suppression and target enhancement method combining first-order direction-controllable differential microphone array beamforming technology and generalized sidelobe cancellation technology is also studied to improve the signal to interference plus noise ratio of the target signal,which provides good conditions for subsequent target classification and recognition tasks.The simulation and external field experiments verify the effectiveness of the above-mentioned direction finding and enhancement method of low elevation angle target based on the differential microphone array.The research results lay a good foundation for the extensive application of differential microphone array acoustic detection nodes in many fields such as border guarding and important place protection.