Acoustic Localization and Decay of the Incoherent Impulse Response
Final rept. 1 Nov 97-31 Oct 98
TEXAS UNIV AT AUSTIN APPLIED RESEARCH LABS
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Applied Research Laboratories, The University of Texas at Austin ARLUT was tasked to study the effects of strong random scattering in acoustic media with macroscopically non-uniform scattering strengths. A statistical, field- theoretic method, previously applied in condensed matter physics and seismology, was introduced to study these effects analytically. Non-uniform random scattering was found to produce phenomena closely related to acoustic localization, which results from uniform scatter. However, non-uniformity also introduces new qualitative signatures not found in localizing systems, including exponential decay of the incoherent impulse response, with universal scaling of the decay time constant. These predictions match features long known empirically to characterize earthquake coda, but not previously explained. The seismic data thus validate the new mathematical techniques, and also introduce useful ways to characterize random scattering within sediments.