Image of the subsurface

The surface of the earth has been mapped and mastered with lidar, photography and infrared by satellites, manned aircraft and drones. Thermal imaginers can even penetrate thin layers of soil. But the Ground Penetrating Radar (GPR) goes much deeper.

GPR is a device used for reading the underground. The transmitter emits wideband pulses that can penetrate glass, wood, concrete and bricks. The receiver identifies reflections of the underground, the recorded wave path showing how deep and how near voids or buried materials are located.


GPR is already used a lot by engineers for detecting cables and pipes. The technology is now further developed to find tunnels that run much deeper. The first prototypes that were presented in 2013 are using much lower frequencies that penetrate ground much better together with new imaging technology that can display clear pictures of deep tunnels.

The technology is now being tested and further developed by (i.a.) the US army for detecting illegal tunnels across borders. The way border agents find tunnels is now basically based on luck. Tunnels are of huge challenge for border patrols because they can begin and end almost everywhere; their entrances and exits are often hidden inside buildings or underneath trees. Initially border control focussed on unmanned aircraft equipped with radar technology that would fly along borders in search for tunnels, but they are almost impossible to detect on such satellite imagery. If successful, the new tunnel detection technology will help agents locate tunnels as fast as they can be dug.

Will there still be a place to hide if we will we be able to dig through the virtual underground infrastructure from behind the screen on ‘google-underground-view’ at some point soon?


leannewijnsma_Air GPR raw and processed data copy


Examples of raw and processed data showing a tunnels

Sources: Homeland Security,

Posted on March 3, 2015

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