Detecting underground enemies

Tunnel digging an art of war: Throughout history, armies that could dig the right tunnels at the right time, got a huge advantage over the adversaries

 

Detecting underground enemies

• Tunnel digging an art of war: Throughout history, armies that could dig the right tunnels at the right time, got a huge advantage over the adversaries. Many examples exist: the collapsing of city walls during medieval sieges, the laying of giant mines filled with explosives under enemy trenches during the first world war, the supply networks of the Ho Chi Minh trail during the war in Vietnam, the Tora Bora cave complex used first by the Mujahideen to oppose the Soviet invasion of Afghanistan and then by the Taliban to oppose the American invasion, etc.
• Modern times: These days, secret tunnels are used to move weapons and people between Gaza and Egypt, and by Kurdish militia operating on the frontier between Syria and Turkey. What happens underground is hard for the enemy to observe. Digging for victory is therefore often a good idea.
• New tech will end all this: Real-time Subsurface Event Assessment and Detection (RESEAD), a project at Sandia National Laboratories in New Mexico, uses novel sensors to make accurate maps of what is happening underground. This will have many civilian applications but it is the military matters that are more compelling.
• Where it came from: The RESEAD grew out of work that was looking at ways of monitoring earth tremors by means of sensor networks. The researchers involved found that the analytical techniques they had developed to handle data so collected were fast enough to process those data more or less in real time. They could detect movement underground in a way that would be militarily useful.

1. Networked sensors used in RESEAD are embedded in the collars connecting sections of borehole casings, and communicate with the surface via wires.
2. This makes them easy to deploy and use. The sensors themselves are a mixture of accelerometers, which pick up vibrations, current detectors, which measure the electrical-resistance of rocks and soil, and subsurface radar.

• Data analysis: The real secret is the way it handles the incoming data. First, these are pre-crunched by powerful hardware built into the sensors themselves. This is a form of parallel processing, greatly reducing the time required by the central receiving computer to finish the job. Second, the mathematical technique employed, a species of finite-element analysis, divides the volume represented by the incoming data not merely into blocks, as is normal in this approach, but into blocks the faces and edges of which can have different properties. This means a block can straddle, say, the interface between a metal pipe and the rock surrounding it. That considerably reduces the number of blocks needed, and further simplifies the calculation.
• Testing on oil fields: In Bakersfield, California, a dense network of oil-related infrastructure exists. The square kilometre picked for testing contained more than a hundred wells, many underground storage tanks and tens of kilometres of steel pipeline. RESEAD produced an accurate map of the area in just ten minutes!
• Summary: How RESEAD sensors would be used in a zone of active conflict remains to be seen. America also has a problem with tunnels under its border with Mexico being used to smuggle drugs and migrants into the country. RESEAD would be able to detect existing tunnels and nip new ones in the bud.

 

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