Research Of Passive Direction Finding Based On All Optic Fibre Array

Beamforming, as one of the primary mission of array signal processing, is commonly used to estimate the bearing of the target passively. Conventional beamforming and MVDR beamforming are two popular methods. The former owns the optimal robustness, and the latter owns high array gain and output signal to noise ratio. However the overall system will confront tremendous amount of computing, and the engineering cost will get increased when these algorithms are applied to large phased array. The fast algorithms of beamforming must be proposed to reduce the computation, accelerate the convergence, and decrease the cost of engineering project. Besides that,on account of the advantages of fibre optical hydrophone array system over piezoelectric transducer hydrophone array system in the respects of performance and engineering application,the research of passive direction finding technique based on all-fibre optical hydrophone array system has been conducted in this article.This article mainly completed the following work.In the first part, the fibre optical hydrophone array system is mainly introduced. As a new type of hydrophone, fibre optical hydrophone has the highest potential in the field of underwater acoustic because of its high sensitivity, strong capability of anti-interference,ability of forming large-scale array easily and simplifing the structure of engineering. In this article,the performances of fibre optical hydrophone and the traditional piezoelectric transducer hydrophone are contrasted, and their characteristics of engineering application are analyzed by listing several parameters and accompanying with pictures.In the second part, the theories of array signal processing is researched. First of all, the performances of the conventional beamforming and MVDR beamforming are contrasted.Secondly,the robustness of MVDR beamforming are studied. Finally,a method aimed at broadband signal,namely the frequency-domain beamforming is put forward and validated by the simulation of MATLAB. In the third part,two kinds of fast algorithms of beamforming are applied, they are, separately, the fast broadband frequency-domain conventional beamforming based on fast fourier transform algorithm and the partially adaptive beamforming based on subarray. The performances of two fast algorithms are researched and validated by the simulation of MATLAB. And the reasonable partition of subarray is put forward.In the fourth part, the sea test system is introduced and the sea test data which are collected by fibre optical hydrophone are processed by the previous theories. The feasibility is validated and some improvement measures are proposed.Compared to the traditional piezoelectric transducer hydrophone array system, fibre optical hydrophone is able to accomplish the mission of passive target detection and bearing estimation more fantastically. Conbined with some beamforming algorithms of high precision,valid robustness and high efficiency, all-fibre optical hydrophone array system has a broad development prospect in the field of underwater acoustic detection.