Much attention has been paid to the new idea of detecting objects by using ocean ambient noise affirmatively. This concept is called acoustic daylight imaging. The authors have tried to detect a silent target object using ambient noise by employing a wide-band beam former consisting of an array of receivers. In experimental results obtained in air, we have applied the delay-sum array (DSA) method and the multiple signal classification (MUSIC) method to successfully detect a silent target object in an acoustic noise field generated by a large number of transducers by using a wide-band beam former. In this paper, we applied the minimum variance (MV) method to detect silent targets as one of the promising high resolution technique of the array signal processing method. The relative power levels near the target obtained with MV and MUSIC were compared with those obtained by DSA. Then, the effectiveness of the MV and MUSIC method was evaluated according to the rate of increase and the direction in the maximum relative power levels.

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