D. Tang, K. B. Briggs, K. L. Williams, D. R. Jackson, E. I. Thorsos and D. B. Percival (2002), `Fine-Scale Volume Heterogeneity Measurements in Sand,' IEEE Journal of Oceanic Engineering, 27, pp. 546-60.
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 grid, hence providing a set of data suited for assessing sediment spatial variability. A three-dimensional sediment porosity matrix is obtained from the conductivity data throught an empirical relationship (Archie's Law). From the porosity matrix, sediment bulk density is estimated from known 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 we found that the spectra can be described by a power-law form. The exponent of the vertical one-dimensional power-law spectra has a depth-dependence and ranges from 1.72 to 2.41. The horizontal one-dimensional spectra have the same form, but with an exponent of 2.2. We found that most of the sediment density variability is within the top 5 mm of sediments, which leads us to believe that sediment volume variability will not have major impact on acoustic scattering when the sound frequency is below 100 kHz. At higher frequencies, however, we expect sediment volume variability to play a role in sound scattering.
Go to next summary or to home page for Don Percival