Acoustical Characterization of the Columbia River Estuary
Abstract
Investigations of near-shore and in-shore environments have, rightly, focused on geological, thermodynamic
and hydrodynamic parameters. A complementary acoustical characterization of the estuarine environment
provides another layer of information to facilitate a more complete understanding of the physical
environment. Relatively few acoustical studies have been carried out in rivers, estuaries or other energetic
environments; nearly all acoustical work in such environments has been done at high acoustic frequencies—
in the 10’s and 100’s of kHz. To this end, within the context of a larger hydrodynamic field experiment
(RIVET II), a small acoustic field experiment was carried out in the Columbia River Estuary (CRE), the
acoustic objective of which was to characterize the acoustic environment in the CRE in terms of ambient
noise field statistics and acoustic propagation characteristics at low-to-mid-frequencies. Acoustically, the
CRE salt wedge consists of two isospeed layers separated by a thin, three-dimensional high-gradient layer.
Results demonstrate that (1) this stratification supports ducting of low-angle acoustic energy in the upper
layer and the creation of an acoustic shadow zone in the lower layer; (2) the spatiotemporal dynamics of the
salt wedge structure during the very energetic flood and ebb tides induce significant variability in the acoustic
environment, as well as significant flow noise across the acoustic transducer; and (3) this flow noise
correlates to current velocity and complicates acoustical observations at low frequencies.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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