Implementation of a Bandpass Filter and Beamforming Algorithms for Source Direction Finding for an ROV

Abstract

A few years ago an underwater sound monitoring system for hearing fishery sound using three hydrophones installed on an ROV has been developed [1]. However, the operation of the system was not successful because of the high level of the self-noise generated by the ROV. Its thrusters had to be turned off to reduce the self-noise and listen to fishery sound clearly. Currently, Korea Research Institute of Ships and Ocean Engineering (KRISO) is developing a light-work class ROV and a similar underwater sound transmission system (USTS) with two largely-spaced hydrophones has been developed for the ROV. Its main purposes are not only to replay underwater sound on the surface vessel for ROV operators but also to identify external source direction. In order to satisfy theses purposes we focus on the minimization of self-noise effect and beamforming algorithm with the largely-spaced hydrophones. To minimize the self-noise effect, a digital bandpass filter with seven filter banks with octave bandwidth was implemented. The conventional delay-and-sum time-domain beamforming technique has been applied to analyze the source direction. To eliminate the spatial aliasing effect induced by the large hydrophone spacing the frequency-difference beamforming algorithms [2] are also considered. The performance of the beamforming algorithms was verified by using a receiver array signal simulator as well as numerical simulations.