Elliptical acoustic particle motion in underwater waveguides

Abstract

Elliptical particle motion, often encountered in acoustic fields containing interference between a source signal and its reflections, can be quantified by the degree of circularity, a vector quantity formulated from acoustic particle velocity, or vector intensity measurements. Acoustic analysis based on the degree of circularity is expected to find application in ocean waveguides as its spatial dependence relates to the acquisition geometry, water column sound speed, surface conditions, and bottom properties. Vector sensor measurements from a laboratory experiment are presented to demonstrate the depth dependence of both the degree of circularity and an approximate formulation based on vertical intensity measurements. The approximation is applied to vertical intensity field measurements made in a 2006 experiment off the New Jersey coast (in waters 80 m deep) to demonstrate the effect of sediment structure on the range dependence of the degree of circularity. The mathematical formulation presented here establishes the framework to readily compute the degree of circularity from experimental measurements; the experimental examples are provided as evidence of the spatial and frequency dependence of this fundamental vector property.

Environmental Acoustics and Intensity Vector Acoustics with Emphasis on Shallow Water Effects and the Sea Surface

“…The primary technical objectives this year involve our measurements from TREX13 conducted in spring 2013, directed towards our participation at the TREX13 workshops in San Francisco (December 2013) and Indianapolis (October 2014). These objectives are: (1) analysis of directional wave spectra and associated synthetic sea surfaces for the TREX13 research teams to model reverberation and time spreading in propagation, (2) estimate the bottom reflection coefficient using both a conventional technique (energy versus arrival angle) and with a new technique based vector acoustics, and (3) estimate and construct intensity streamlines that be used to better understand the forward propagating field.…”

“…Our work this year on TREX data is organized into three areas concerning: (1) Directional Waves, (2) Comparative estimates of bottom loss using conventional (time and angle) technique and vector based technique, and (3) estimating energy flux streamlines in propagation measurements. Preliminary results were first discussed at the TREX workshop in December 2013 with subsequent results since this time to be discussed at the upcoming workshop in October 2014.…”

“…The degree of circularity is a non-dimensional vector quantity relating to acoustic particle velocity [2]. For example, if two wavefronts are in phase, acoustic particle motion falls along a line with an orientation related to the relative magnitude of the direct and reflected field.…”

“…This motion can be succinctly described by degree of circularity, which itself is a vector and defined as follows [2] ,…”

“…Our studies in vector acoustics and in particular vector circularity as summarized in [2] has led to potential applications involving the detection of sources in shallow water where match field approaches have performed poorly. Though a source detection application is yet fully realized, the measurements vector circularity from TREX13 (item 2 in RESULTS), are pointing to related geoacoustic application.…”