Fine-scale volume heterogeneity measurements in sand

As part of the effort to characterize the acoustic environment during the high frequency sediment acoustics experiment (SAX99), fine-scale variability of sediment density was measured by an in situ technique and by core analysis. The in situ measurement was accomplished by a newly developed instrume...

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Bibliographic Details
Published in:IEEE journal of oceanic engineering 2002-07, Vol.27 (3), p.546-560
Main Authors: Dajun Tang, Briggs, K.B., Williams, K.L., Jackson, D.R., Thorsos, E.I., Percival, D.B.
Format: Article
Language:English
Subjects:
Acoustic measurements
Acoustic scattering
Acoustics
Backscatter
Conductivity measurement
Density
Density measurement
Exponents
Frequency
Laboratories
Marine
Sand
Sediments
Sound
Spectra
Three dimensional
Volume measurement
Wavelength measurement
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Summary:As part of the effort to characterize the acoustic environment during the high frequency sediment acoustics experiment (SAX99), fine-scale variability of sediment density was measured by an in situ technique and by core analysis. The in situ measurement was accomplished by a newly developed instrument that measures sediment conductivity. The conductivity measurements were conducted on a three-dimensional (3-D) grid, hence providing a set of data suited for assessing sediment spatial variability. A 3-D sediment porosity matrix is obtained from the conductivity data through an empirical relationship (Archie's Law). From the porosity matrix, sediment bulk density is estimated from known average grain density. A number of cores were taken at the SAX99 site, and density variations were measured using laboratory techniques. The power spectra were estimated from both techniques and were found to be appropriately fit by a power-law. The exponents of the horizontal one-dimensional (1-D) power-law spectra have a depth-dependence and range from 1.72 to 2.41. The vertical 1-D spectra have the same form, but with an exponent of 2.2. It was found that most of the density variability is within the top 5 mm of the sediment, which suggests that sediment volume variability will not have major impact on acoustic scattering when the sound frequency is below 100 kHz. At higher frequencies, however, sediment volume variability is likely to play an important role in sound scattering.
ISSN:0364-9059
1558-1691
DOI:10.1109/JOE.2002.1040937