Minimum Variance Distortionless Response (MVDR) technique is one of the signal processing ways for noise reduction. Its principle is to minimize the output power of the signal. This study simulated an underwater acoustic field using ray acoustic method. The acoustic field consists of a signal source, multiple noise sources and a line array hydrophones. The signal source is ship-radiated noise. The simulated combining signals received by the hydrophone array are used to restore the original signal source by MVDR technique. The study discusses the different objective functions given in MVDR in order to restore the original source. Then, the results are compared in computing time, effectiveness and adaptability. The results indicate that MVDR can be used to restore the original signal source with very high correlation coefficient up to 90% between the original signal and the restored one.
This study investigates the performance of a passive time-reversal mirror (TRM) combined with acoustic ray theory in localizing underwater sound sources with high frequencies (3–7 kHz). The TRM was installed on a floating buoy and comprised four hydrophones. The ray-tracing code BELLHOP was used to determine the transfer function between a sound source and a field point. The transfer function in the frequency domain obtained from BELLHOP was transformed into the time domain. The pressure field was then obtained by taking the convolution of the transfer function in the time domain with the time-reversed signals that were received by the hydrophones in the TRM. The location with the maximum pressure value was designated as the location of the source. The performance of the proposed methodology for source localization was tested in a towing tank and in the ocean. The aforementioned tests revealed that even when the distances between a source and the TRM were up to 1600 m, the distance deviations between estimated and actual source locations were mostly less than 2 m. Errors originated mainly from inaccurate depth estimation, and the literature indicates that they can be reduced by increasing the number of TRM elements and their apertures.
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