Wave separation and signal isolation via line-scan supersonic acoustic holography.

Abstract

Pressure signals scattered from a target and received by a line array can be buried in noise having similar frequency content, such as reflections from nearby interfaces or objects adjacent to the target. In such circumstances, it may be difficult to isolate the desired signal through the use of standard linear time-invariant filtering techniques, because the frequency content of the signal and noise are identical. Supersonic line-scan holography, however, can be used in many such circumstances to achieve signal isolation by backpropagating the acoustic signal to a focal region, spatially and temporally filtering the signal around the focal region, and forward-propagating the isolated signal to the original array location. This technique was used to measure the bistatic angular scattering pattern of a small target driven at resonance. This was done in a water tank using a hydrophone scanned along a line. A demonstration of how this method was used to isolate the signal from larger, overlapping reflections will be given. The method was also applied to backscattering measured with a scanned transducer and fixed proud cylinder resting on sediment. [Work supported by ONR.]