Detection and target-strength measurements of buried objects using a seismo-acoustic sonar
By: Patrick W. Hall
Publisher: Naval Postgraduate School; Available from National Technical Information Service
Published: 1998
Place of publication: Monterey, Calif; Springfield, Va
Language: eng
Number of pages: 62
Description: This thesis describes the results of field experiments in which seismo-acoustic interface (Rayleigh) waves were      employed to detect and measure the target strength of mine-like test objects buried in the near-surf zone. These      experiments were conducted as part of an ongoing NPS research program to develop a seismo-acoustic sonar      system for the detection of buried mines in the surf and, near-surf zones. An experimental seismo-acoustic sonar      system, using linear force actuators as the wave source and three-axis seismometers as receivers, was deployed      at a beach test site. The target strengths of two mine- like test objects, a compressed gas cylinder and a      gunpowder can, were measured as a function of target mass and for various emplacement conditions, e.g. very      wet sand, not very wet sand, partially buried, completely buried, completely buried and washed over for several      days. "Vector polarization filtering" was employed to separate the reflected signal due to Rayleigh waves, for      which the particle motion is elliptical, from that of body (P and S) waves, for which the particle motion is linear.      The target strength was generally found to increase with increasing target, mass. Typical values observed ranged      from approximately -20dB to -10dB for target masses of 70 to 290 kg. Curiously, it was observed that the      elliptical particle motion of the reflected wave was of the opposite polarity for those targets which were buried,      but slightly exposed, compared to those which were completely buried. It is not known at this time whether this      is due to the depth-dependent properties of Rayleigh waves, or whether it is a result of the conditions of source      and target emplacement.
Notes: "December 1998."

Thesis advisor(s): Thomas G. Muir, Steven R. Baker.

Thesis (M.S. in applied Physics) Naval Postgraduate School, December 1998.

Includes bibliographical references (p. 59-60)

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US Marine Corps (USMC) author.

dk/dk cc:9116 02/03/99