Exploring autoproduct fields in three-dimensional acoustic environments: Simulations and experiments

Acoustic remote sensing and source localization are fundamental topics in underwater acoustics, with applications ranging from navigation, environmental monitoring, surveillance and reconnaissance. Traditional signal-processing techniques for such tasks typically rely on frequencies within the bandwidth of acoustic recordings. Recent developments, however, have shown that it is possible to extract environmental and source location information at frequencies outside a recorded signal’s bandwidth using the frequency-difference and frequency-sum autoproducts [Worthmann and Dowling, J. Acoust. Soc. Am. 141, 4579–4590 (2017)]. Previous acoustic autoproduct studies have involved sound fields that primarily vary in two spatial dimensions. This presentation provides simulation and experimental autoproduct-based source localization results using vertical-array recordings collected in the fully three-dimensional four-ray-path acoustic field arising in Lloyd’s mirror environment augmented with a vertical reflecting surface. The experiments were conducted in a 1.07-m-diameter freshwater tank using short Gaussian-enveloped pulses having a nominal bandwidth of 40–110 kHz. Time gating of the recordings was used to remove the tank sidewall and bottom reflections. The importance of acoustic reflection from the added vertical surface is explored by varying its distance from the plane defined by the source and receiving array. Comparisons between simulated and experimental localization results are presented. [Work sponsored by ONR.]