Acoustic and Seismic Systems

Use mechanical compliance and resonance of mines for detection. Several different sensors fall under this category: laser doppler vibrometers (LDV), radar, ultrasonic devices, and microphones. Very low false positive rate and high rates of detection with sophisticated signal analysis. Unaffected by weather/moisture. Complements ground penetration radar sensor well as the two use completely different physical properties of mines.

Limitations:

  • One mine diameter depth limit
  • 125-1,000 secs to analyse 1m^2, though time can be reduced by N with N sensors.
  • Vegetation can obscure analysis of surface depending on the system used

Conventional Approach:

Sound waves are emitted into a the soil. Use low frequencies for wider range of detection and higher frequencies for higher resolution imaging. Sound waves are reflected on boundaries between materials of different acoustic properties (different impedance), which is then detected. Good penetration to wet/heavy ground such as clay. Sometimes requires direct mechanical coupling with the soil. Problems exist with distinguishing small reflected waves with more dominant source waves and ground contours/irregularities, requires good signal processing technology.

Acousto-seismic:

Sound waves penetrate the surface of the ground (mechanical coupling not required) and causes seismic motion within the ground, known as acoustic-to-seismic (A/S) coupling. Landmines buried underground will resonate and cause distinct changes in seismic motion. The vibrations are detected at the surface remotely by LDVs or microwave vibrometers. A great deal of research is going into LDV-based A/S landmine detection.

Non-linear:

Use the non-linear nature of the soil-mine interface to generate sum and difference frequencies from a combination of two or more incident acoustic waves of different frequencies. Basically, uses a system of two or more A/S sensors.

Ultrasonic (sonar):

Proposed mainly for use in detecting mines buried underwater in rivers, canals, etc.

Sources:

http://www.eudem.vub.ac.be/technologies/technology.asp?tech_id=18
http://www.acoustics.org/press/155th/scott.htm

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