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Acoustic vector sensor measures both acoustic pressure (scalar) and the three components of acoustic particle velocity (vector). Azimuth and elevation angles of the sound source can be obtained, thus enabling to have a three – dimensional picture of the sound source in the environment. AVS has several advantages over conventional pressure only sensors (scalar) such as high front to back ratio, deep nulls at 900 to the maximum response axis, narrow beam-width (higher directivity) with shorter aperture, resolves left – right ambiguity without an extra array that is being practised in towed array sonar, gives a 3-D picture of the sound source with a single array while horizontal and vertical arrays are required for the same function if a conventional sensor array is used, the array elements can be sparsely populated unlike the λ/2 spacing criteria for the conventional sensor array. This team has developed and evaluated inertial type AVS over the last few years and proved its characteristic functioning through controlled underwater acoustic measurements. The paper presents the results of AVS array fabricated and evaluated in the lake environment: free-field far-field conditions, stationary and moving source locations and compared the measurement results through signal processing algorithms developed for AVS. The acoustic evaluation was performed with the eight element vertical array hung from a floating platform to a depth of 3m below lake water surface. The acoustic response of the sensors indicates its capability to differentiate L-R ambiguity of a motor boat that was moved from place to place ahead and across the vertical array at far-field free-field conditions and also while the boat was moving. Experiments were also performed with tone-burst and half-sine at different frequencies at various depths of the Tx while keeping Rx at a particular depth but for a fixed distance of separation between Tx & Rx. The phase reversal of the incident signal by the Rx for above and below Tx and port and starboard changes were also observed. The sensors exhibited 19-23dB among the different axis. The DOA results signify the advantages of AVS and the results summarise the lake trials for the effective use of AVS for detection, thus giving an excellent insight on the performance.
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