The Study Of Underwater Acoustic Image Measurement Technology

Underwater acoustic image is a special passive acoustic imaging technology,which can give the spatial distribution of noise sources Applied in aero acousticsat the very beginning,underwater acoustic image has good results in noise-sourcedistribution measurements of railway trains and internal noise measurements inthe large engines,and is successful to guide the vibration and noise reduction ofthese large engines The vibration and noise reduction of ship also receives muchconcern Enlighten by aero acoustic image measurement,the paper researches onunderwater acoustic image measurement to maalyze the spatial distribution ofnoise sources in shipsThe core algorithm of underwater acoustic image measurement is dynamicsfocus beam forming whose principle is similar to normal beam forming Thedifference between the two methods is that the underwater acoustic imagemeasurement is applied in near field in which spherical wave compensationwhose value is related to spatial position is taken；whereas the normal beamforming takes plane wave compensation By using spatial scan,the spatialdistribution of noise sources is judged by the beam forming power output indifferent pixel pointsBecause of the complex underwater environment,it is difficult to lay a largehigh-accuracy half-wavelength array．Thus it is normal to use sparse array inunderwater acoustic image measurement In the paper,~equency-divisionintegrated technology and virtual array technology are applied to overcome theinfluence of sparse array．The underwater acoustic channel is coherent multi-pathchannel The paper combines virtual time reversal mirror algorithm and virtualarray algorithm to overcome multi-path interference,which achieved good effectThe resolution of underwater acoustic image measurement is related to array length,the distance to the target and the band of signal The resolution is not SOgood to low frequency sources w-hen the same target distance and array length aJ'efixed Thus researches on MVDR focus beam forming and STMV focus beamforming are applied to improve the resolution of low frequency sound sourcesThere will be coherent interference for each other when there are multi soundsources The influence of the strong sources to weak ones is severe Therefore,two anti-interference technologies are researched One is null beam forming innear field based on adaptive interference cancellation,and the other is based onBartlett weight The methods can overcome coherent interference and enhance thequality of underwater acoustic image in multi sound sourcesMoreover,the scanning depth will afl'ect the accuracy of the underwateracoustic image w-hen the measurement array is horizontal For the horizontal arraysince the acoustic image measurement is a two-dimensional image in certainscanning depth,scanning depth and actual depth of sources must be the Sa2rle,otherwise there will be measurement error,which 1eads the fact that the hemeasurement of the sound source depth is a key issue which afl'ects the accuracyof measuring for horizontal array．Because a horizontal array is non-directional inthe vertical direction,the measurement of source depth of horizontal array isseldom discussed in literatures The paper proposes the viewpoint that for thespecial navigation across the array using the location result of underwater acousticimage measurement to certain depth the source dcepth can be achieved fromgeometrical relationship of the sources and array Two depth measuring methodsare discussed in the paper One is geometric method and the other is circleintersection method The former is suitable for the horizontal array and the latteris for the array with a certain angle oftiltBased on the passive location,a preliminary study is done on the radiationnoise sources separation by underwater acoustic image measurement The paperresearches on the extraction methods of noise source signal,and the performance of signal separation is examined in the time domain and~equency domain,respectivelyThe paper does simulation research on underwater acoustic imagemeasurement Ngorithms based on the horizontal array,ve~ical array and planararray,and the various underwater acoustic image measurement algorithms areverified through four horizontal array voyage tests...