Studies On DOA Estimation Of Two-Dimensional Pressure-Gradient Vector Transducer

It is well known that sound wave has both scalar quantity field and vector quantity field. Compared with the pressure hydrophone, vector transducer can provide both the information about pressure (scalar quantity) and particle velocity (vector quantity) of the sound field, which offers more possibilities for signal processing. A single pressure hydrophone is omni-directional and can not be used to estimate the DOA of acoustic signal. But single vector transducer can be used to measure the pressure and particle velocity at some point of acoustic field simultaneously, so a single vector transducer can achieve the estimation of DOA. In this thesis, the theoretical deduction, computer simulation and analysis of experimental data, about estimation of multi-source parameters with single vector transducer for pressure gradient, transducer, using method of correlation equations are given. The main contents are:1. The development of vector transducer and corresponding methods of signal processing is reviewed. The working principle of co-vibrating type and pressure-gradient type of vector transducers are studied, and their mathematical models are established. The direction patterns of 2-dimensional vector transducer for different type of combination are given by simulation.2. The correlation of pressure and particle velocity of acoustic field is studied. A multi-sources distinguishing method is presented. A series of correlation equations are obtained for the correlating of pressure and particle velocity in plane wave, and DOA of sound sources are obtained by solving this system of equations. In this thesis, the system of correlation equations is solved respectively for narrowband uncorrelated signal, broadband signal and correlated signal are studied. The multi-sources distinguishing method with known direction interfere is presented, for both uncorrelated narrowband and broadband cases.3. It is the first time to study the gain in SNR using correlation of pressure and particle velocity for two-dimensional pressure-gradient vector transducer, under background of isotropic white noise, and the accuracy of solution of correlation equations at different arrival angel is simulated. Although the conclusion is deduced at narrowband case, but it keeps force also for broadband signal. According to the study, correlation equations with smaller error should be chosen to estimate the DOA in case of less sources. 4. GA (Genetic Algorithms), DE (Differential Evolution) and HDE (Hybrid Differential Evolution) are applied on the optimization of non-linear correlated function of pressure and particle velocity, the principle and steps of the three methods are introduced, the convergence speed, convergence precision and costing time of three methods are compared based on the optimization problem which needs to be solved in this thesis.5. Computer simulation and experimental data processing are applied with the DOA estimation based on solving correlation functions. Computer simulation is given mainly for the case of two sources, including uncorrelated narrowband signal, broadband signal and correlated signal. The estimation error of DOA in case of more than two sources is also provided. Directional pattern of vector transducer at different frequency is measured in anechoic tank of Northwestern Polytechnical University, and direction estimation of single source is verified by method of sound energy flux. Direction estimation method of two uncorrelated narrowband signals, broadband signal and sound signal with known direction interference are verified by experimental data of getting from experiment carried in Feng-Jiashan reservoir. Multiple broadband sources distinguishing and DOA estimation of signal interfered by known direction angle interference is verified by experimental data getting from experiment carried in sea area of Zhou-Shan.