SIREM: an instrument to evaluate superdirective and intensity receiver arrays

Pressure gradient arrays have been in use within the acoustic community for several decades. Historically most underwater acoustics measurements employing pressure gradient arrays have used the superdirective array whereas air applications have relied on the intensity array approach. Intensity arrays based on pressure sensors require the same hardware (and equally rigorous hardware tolerances) as superdirective arrays. The difference between the two methods lies in how one processes the received signals. One obtains the intensity by multiplying pressure and pressure gradient signals; The superdirective solution is obtained by summing the pressure and the pressure gradient signals. The measurement objective dictates which solution is better for a given experiment. The Defence Research Establishment Atlantic (DREA), in collaboration with Guigne International Ltd., has developed a 6-channel hydrophone array which will be used to explore the processing advantages of both methods. Two configurations of the system will be examined: a tri-axial array of dipoles enabling measurements along the x, y, and z axis, and a 6-channel linear array configuration enabling measurement of gradients up to 5/sup th/ order along a single axis. In this paper, the array configurations will be outlined and the impact of system noise on the processing methods will be described.