Surface Waves for Remote Demining

The indiscriminate laying of anti-personnel mines in unmapped areas is a serious blight worldwide and particularly in those countries where local wars are in progress or where wars have ceased and the civilian population has inherited their mine legacy.Countries particularly bedeviled by the anti-personnel mine problem include Angola, Mozambique, Bosnia, Cambodia, Vietnam, Rwanda, Somalia and Kosovo.

To date, thousands of civilians have been killed or maimed by anti-personnel mines.Concerned international organizations such as the Red Cross restrict their activities to treating the victims.Some other international organizations are prolific with words and mine hype but are short on action.Effectively, serious demining is carried out by a number of small humanitarian organizations such as Norwegian People’s Aid, the HALO Trust and the Mines Advisory Group (MAG).Current demining techniques are primitive and depend on the locating of individual mines by metal detectors and probes and the deactivation of individual mines by the hazardous procedure of digging them up with trowels.The latest mines have a high plastic content and often contain too little metal to register on the metal detector.Demining operatives are then reduced to probing as the main technique of discovery.It is a salutary thought that over an eight year period forty three expert HALO deminers were killed or maimed.

New developments in technique are required to lessen the risk to demining operatives and to provide a cost-effective clearing scheme for substantial areas of unmapped minefield.Little attention has been paid so far to remotely-operated techniques for mine clearance.Radio-controlled robot vehicles have been used, but these are expensive and easily-damaged by exploding mines.Normal seismic methods for attacking the mine fuse from a distance are not practicable because most seismic energy is propagated as compressional and shear waves deep into the rock strata well below the surface where the mines are laid.However, a number of designs of relatively inexpensive seismic sources can be deployed to generate high amplitude Rayleigh surface waves.These are low frequency ground waves in which the particle motion just below the surface is anti-clockwise to the wave travel and is in the form of an ellipsoidal or cylindrical shift in the near-surface ground to produce periodic displacement of the surface.Rayleigh waves of very large amplitude are invariably seen in earthquakes and are responsible for the shaking of the ground which causes building collapse.Rayleigh waves appear as 'ground roll' in seismic exploration.Here, because of their large amplitude, they tend to swamp seismic reflection and refraction signals and have to be filtered out from the seismic record.In the context of remote demining, such surface waves provide a means of impacting a ground acceleration-derived force of relatively high amplitude on the mine fuse in order to detonate the device at a distance (Melvin: UK patent application: GB 2335166A).Such a technique opens the prospect of remotely demining areas of laid mines, thus making demining safer for operatives.