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Buried Object Detection

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Final rept. 15 Apr 87-14 Apr 88

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An acoustic scheme for buried object detection is thought to involve a sound source above the ground and a microphone as a receiver. In the simplest scenario, an airborne acoustic pulse would be transmitted, strike the ground surface, propagate through the pores and reflect off the surface of a non-porous object. The microphone would then be used to detect the pore-fluid echo. These ideas were first considered in a sound tube with spherical beads used to porous medium. Experimental measurements of the pore-fluid propagation constants were compared to rigid framed model calculations for model verification. These experimental and theoretical results were then used to make predictions of the sound levels required to detect objects buried a few centimeters in outdoor soils. In addition, we chose a detection criteria which required that the pore- fluid echo be at least 12 cycle behind the pulse reflected from the ground surface. This criteria is quite arbitrary and conservative, but it allows for source specifications and from an experimental point of view appears as a realistic criteria for detection. The models allowed for prediction of reflection losses, propagation losses, phase velocities and source levels based on burial depths of a few centimeters. Using these calculations various off-the- shelf acoustic sources were considered and it was realized that none were available to use existing sound sources to demonstrate that non-porous objects could be detected a few centimeters below the surface of institutional or grass soils. Research to develop a sound source which meets the original design criteria is on-going.

Subject Categories:

  • Acoustic Detection and Detectors
  • Acoustics

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