Roughness Spectra and Acoustic Response from a Diver-Manipulated Sea Floor

Abstract

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An Experiment in High-Frequency Sediment Acoustics: Sax99

“…There is no evidence to suggest that scattering from gas bubbles on or within the sediment was important during SAX99. Preliminary modelling of scattering from sediment heterogeneity based on parameters given in Table 2 of [3] produce backscattering levels well below those for sea oor roughness scattering (about 25 dB lower at angles below the critical angle, and about 17 dB lower above the critical angle). Thus, we consider only scattering from sediment roughness.…”

“…a1. [3]. Investigations of backseattering from regions of the sea oor with well de ned treatments (or manipulations) are described in Richardson at al.…”

“…An experiment in HF sediment acoustics: SAX99 Grazing Angle (deg) environmental descriptor is the spectral strength of roughness at the Bragg wavenumber k3 = 2kcos i, where k =27r/iL is the acoustic wavenumber in water, }L is the acoustic wavelength in water, and 9, is the incident grazing angle. Stereo photogrammetric roughness data for SAX99 are now becoming available [3] and provide estimates of 1-D roughness spectra. In addition, Tang's in situ conductivity probe data has been used to obtain 1-D roughness spectral estimates.…”

“…The model curves in Figure 2 are based on stereo photogrammetric data measured at the BAMS tower site on 23 October and 5 November 1999 [3]; the spectral levels are nearly the same for these two dates in the region of the Bragg wavenumbers for backscatter. A power-law fit was made to the average l-D spectrum for these dates over the spatial frequency (Ill) range of 0.2 to 2.0 cm" which contains the relevant'Bragg spatial frequencies (e.g., k, /(27r) = 0.505 cm" at a,-= 15°).…”

“…The goals of this paper are twofold: rst, to provide an overview of the entire SAX99 measurement program, and second, to give initial results from APL-UW (Applied Physics Laboratory, University of Washington) measurements and modelling, the latter based largely on NRL SSC (Naval Research Laboratory, Stennis Space Center) environmental measurements. Separate papers in this conference [3][4][5][6][7] describe other initial results.…”