Researches On The Measurement Of Underwater Image Using Focused Beamforming

The analyse of the distribution map of ship's noise sources has great significance, it can determine the positions of main radiations in the target. This technique can be used to measure the moving target's near range position. Further more, the study of noise sources' characteristic is important for developing the technology of reducing the vibration and depressing the noise, and it is also very useful for examining the malfunction of the ship.A method using focused beamforming to measure the distribution map (underwater image) of target's noise sources is presented in this dissertation. There are two measurement models, level linear array and vertical linear array. Level linear array can measure the target image on water level, but the multi-path interference of underwater acoustic channel may affect the quality of it. In order to solve this problem two methods are adopted, virtual time reversal mirror and virtual array, both of them can depress the interference very well. Vertical linear array can measure the distribution map of the target's noise sources in vertical plane and because of its vertical directionality it's almost unaffected by the multi-path interference. But as the same to level linear array, ordinary vertical pressure sensor array can not distinguish whether the target is left or right (neither front or back). In this dissertation, we take vertical linear array for example adopting vector sensor array to solve this problem. Using the combined information of pressure and particle velocity can get unilateral directionality by some proper combination or get the target's azimuth angle by histogram azimuth angle estimation firstly and then use focused beam forming to scan. The two methods can both solve this problem very well, and the second method can even get the three-dimensional image of the target's noise sources.The emulational results have demonstrated the validity and solidity of the arithmetic and the experimentation in air has validated its feasibility. Finally, the real time software empolded on LH-CTS2-8NX-201DSP processor demonstrates its practicability.