Study On The Array Processing Techniques For Ship-radiated Noise Measurement

As an effective tool of estimating the ship’s acoustic stealth capability, the radiated noise measurement become an indispensable method in the development of navel equipment. Aiming at the more difficult measuring task, the line spectrum extraction techniques and broadband array processing techniques are systematically and deeply studied in this paper to accurately acquire the ship radiated noise. The main contributions are as follows:1. The basic theories of ship radiated noise measurements are discussed and then the main noise sources and their spectral characteristics are analyzed. The analyzing methods of frequency-band sound pressure level(SPL), spectral level and overall level with a single hydrophone are provided.2. Based on the principle of the pass-by characteristics, a novel method of locating the equivalent acoustic center is proposed in this paper. Experimental results demonstrate that the proposed method is feasible to locate the ship’s equivalent acoustic center under the lower SNR and an unobvious pass-by characteristic circumstance.3. A mathematical model of linear array in near field is established, and a design method of conventional beamformer is given. Then, some sidelobe control methods such as Dolph-Chebyshev weighting are also provided, and the performance of these methods, as well as the influence on the beamwidth and sidelobe are analyzed. To solve the beampattern distortion phenomenon caused by delay quantify errors, a method using the FIR fractional delay filters to realize fractional time delays period is studied. From the navigation experiment, we illustrated the frequency characteristics of the moving target’s radiated noises acquired by the linear array, and the results show that FIR fractional delay filters provides better performance in near field compensation, and with which the processing using a linear array can effectively improve the signal and reject the noise interferences, the results are consistent with that of a single hydrophone.4. Based on the nested array, a design method of constant beamwidth beamformer is established. Beamforming for noise sources located in the near field in studied. A near field compensation method is outlined, and the effectiveness of the proposed method is illustrated by numerical examples. The results of the static experiment show that broadband array processing based on nested linear array can effectively improve the signal and reject interferences, and the results are consistent with that of a single hydrophone.