Development and performance test of an underwater sound transmission system for an ROV

Recently Korea Research Institute of Ships and Ocean Engineering has developed an underwater sound transmission system (USTS) for a light-work class ROV. Its main purposes are not only to measure underwater sound using two hydrophones and replay it for ROV operators on the surface vessel but also to identify source direction. The subsea unit of the system is composed of amplifiers, filters, an ADC, and a controller. In order to minimize self-noise effect a digital bandpass filter was implemented using an FPGA. The surface unit of the system estimates source direction using a beamforming algorithm and generate sound using stereo speakers. At the moment the conventional delay-and-sum beamforming algorithm has been implemented. Its performance was verified by using a simulator, which generates receiver array signals constructed by plane waves. The implemented beamforming algorithm will be substituted by other, such as frequency-difference beamforming to improve the source direction finding performance. Its mathematical derivation is briefly described and numerical simulation shows that it can effectively eliminate the aliasing effect for a system with large sensor spacing.