Shear wave excitation in unconsolidated ocean sediments

Abstract

Fo values was considered. The second describes the contours as the output of two second-order systems, one for sentence phrasing (whose excitation pulses are related to the sentence structure) and one for syllable emphasis. Masking levels for maskers consisting of harmonic complex tones structured in time and frequency (in German) [43.66.Dc, 43.66.Fe, 43.66.Nm, 43.66.Mk, 43.66.Ki]--Henning Alphei, Drittes Physikalisches Institut, Universiti•t Gbttingen, Fed. Rep. Germany, Sept. 1984 (Dipl.--Phys.) Masked thresholds are obtained for a 1200-Hz test tone masked by harmonic complex tones (always with a fundamental frequency of 40 Hz). The individual harmonics of the masker (up to 60) are added in sine phase with amplitudes decreasing as 1/f Hence, the resulting waveform of the complex tone has a pronounced temporal structure. The masker's spectral structure is altered by omitting either the low-or the highfrequency components. For these low-pass and high-pass versions of the complex tones, a pronounced maximum of the masked thresholds is found when the masker's cutoff frequency is near to the test tone frequency. This effect can be explained qualitatively by the temporal structure of the masker's envelope at the test tone frequency. In order to differentiate between the effects of temporal and spectral resolution of the ear, additional measurements at various masker levels are performed. The results indicate that for the test tone frequency below the masker frequency the masked thresholds are determined by temporal resolution. For the test tone frequency within the masker frequency range the masked thresholds depend both on temporal and spectral resolution. For the test tone frequency above the masker frequency range the masked thresholds are determined by spectral resolution and the presence of combination tones. Thesis Supervisor: Prof. Dr. M. R. Schroeder Copies are available from the author: Henning Alphei, Drittes Physikalisches Institut, Btirgerstr. 42-44, D-3400 G6ttingen, Fed. Rep. of Germany. James D. Johnson, LCDR, USN, NavalPostgraduate School, Monterey, C•4 93943, Dec. 1984 (M. Sc., Eng. ,4coust.) A system is described which measures the conductance and susceptance of hydrophones and provides as an output a plot of the complex admittance and computed values for the cou-2195

The effects of sediment porosity on acoustic reflection and transmission at the seafloor

“…Some of the experimental results [e.g., Ingenito and Wolf (1976), McDaniel and Beebe (1980), Chapman and Ellis (1984), Beebe and Holland (1986), Hughes et al (1990)], however, indicated that the effect of the sediment rigidity could be significant for various environments. Modeling efforts [Fryer (1978), Vidmar (1980), Holland (1985)] that considered the sediments as viscoelastic attempted to determine the bounds of validity for the fluid approximation as a function of frequency and seafloor environment.…”