Analysis of the advantages and complexities of acoustic vector sensor arrays

Abstract

The hydrophone, an omnidirectional underwater microphone, is the most common sensor for listening to underwater sound. Directional sensors, however, have many important applications. Acoustic vector sensors, one important class of directional sensors, measure acoustic scalar pressure along with acoustic particle motion. With this additional vector measurement, vector sensors feature many advantages over conventional omnidirectional hydrophone sensors: improved array gain/detection performance, enhanced bearing resolution, the ability to “undersample” an acoustic wave without spatial aliasing, and the capability of attenuating spatial ambiguity lobes, e.g., left/right ambiguity resolution for a linear array. Along with their advantages, however, vector sensors also pose additional practical complexities: greater sensitivity to non-acoustic, motion-induced flow noise at low frequencies, requisite knowledge/measurement of each sensor's orientation, management of different sensor types (pressure and particle motion) that each with different noise properties/calibration requirements, and adaptive processing can become difficult in a snapshot limited regime since each vector sensor is made up of up to four data channels. This paper will explore the virtues and limitations of vector sensor arrays in the presence of realistic ocean noise fields and system imperfections, including their effects on array performance (gain, beampatterns, etc.) supported by theoretical analysis and illustrative examples.