In:
The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 74, No. 3 ( 1983-09-01), p. 960-972
Abstract:
The loss rates for propagation of 5- to 40-Hz acoustic normal modes recorded on a shallow, sandy bottom off Nova Scotia were found to be strongly dependent on the azimuth and range of propagation. Beyond a certain range the propagation loss rates for signals just below the nominal cutoff frequency (calculated assuming a range-independent acoustic medium) differed only insignificantly from those just above the nominal cutoff, suggesting that propagation of signals at long ranges below cutoff may not be less efficient than those slightly above cutoff. Although it is commonly thought that scattering, conversion to shear waves, and surface wave generation are important causes of acoustic wave attenuation at low frequencies, our data indicate that nearly all loss arises from sediment attenuation. These results are of general interest because the near seafloor geology of many continental shelves is similar. We are less certain of the reasons for the lack of success in modeling the observed propagation loss using the parabolic approximation for frequencies well above the cutoff frequency. We do know that the spatial variation of the sound velocity, density, and thickness of the water column was not measured in sufficient detail during the experiment. More reasonable fits to the observed propagation loss at lower frequencies suggest that the parabolic approximation was not the major source of modeling error.
Type of Medium:
Online Resource
ISSN:
0001-4966
,
1520-8524
Language:
English
Publisher:
Acoustical Society of America (ASA)
Publication Date:
1983
detail.hit.zdb_id:
1461063-2
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