Studies on underwater acoustic vector sensor for passive estimation of direction of arrival of radiating acoustic signal

A passive underwater surveillance system performs the function of detection and localisation by utilising the acoustic emissions from the source, whilst itself remaining concealed. The conventional technique employs an array of hydrophones (measure the scalar pressure), wherein the size of the array is dependent on the desired angular resolution and the wavelength of the signal to be monitored. The "vector" sensors, on the other hand, measure the scalar pressure as well as the orthogonal components of particle velocity using a co-located sensor and offer decided advantages over the traditional solution due to their smaller size and frequency independent performance (over the frequency range specified for constituent particle velocity sensors). This paper presents studies on a prototype underwater acoustic vector sensor. The present approach employs a tri-axial accelerometer as a co-located particle acceleration sensor, and along with a hydrophone it provides four sets of measurements of an acoustic field. The parameter (Direction of Arrival) estimation has been carried out using both subspace based methods as well as beamforming technique for demonstration of the acoustic vector sensor system in the lab environment and its performance analysis.