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10 June 2005 Acoustic to seismic ground excitation using time reversal
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The detection of land mines using acoustic and seismic excitation is problematic due to the small amplitude of vibration that can be induced in the soil. Increasing this level reduces the requirement on a sensor’s noise floor and may be useful for nonlinear detection. For these experiments, an array of loudspeakers broadcast orthogonal noise signals to excite ground vibrations. A contacting geophone measures the system’s vibration response to all signals. We then correlate an excitation signal with the measured vibration response to approximate the system impulse response between a loudspeaker and the geophone. Time reversing the impulse response generates a pre-filter for each loudspeaker. Subsequent signals transmitted through the pre-filter and loudspeaker tend to be temporally focused at the receive location as well as greater in amplitude. Results compare vibration amplitude with and without the time reversal process for spatial locations near the mine.
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Brad Libbey and Doug Fenneman "Acoustic to seismic ground excitation using time reversal", Proc. SPIE 5794, Detection and Remediation Technologies for Mines and Minelike Targets X, (10 June 2005);


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