I Does a working underground tunnel detection technology exist?

1. Mar 5, 2017

FTM1000

from what i readed in news articles about smuggling tunnels in the US-mexico border and terrorists tunnels in the israel-gaza border it seems that there is no technology that can detect deep(few dozens of meters) underground tunnels and that there is only technology for detecting underground excavation of tunnels.
but after a further search in google on things like Ground Penetrating Radar(GPR) i saw many websites of companies that claim to have/sell devices that can detect tunnels 30 meters deep in the ground(and even specify that it is for military purpose) which is the dept of at least some of the tunnels.

does 30 meters is the edge for GPR technology in detecting tunnels? or that technology can advance to detect tunnels 50 and 60 meters in the ground?.
and what about other technologies? in some news article i heard about the possibility of detecting tunnels with gravimeters, it might be actualy feasible in the future?.

2. Mar 5, 2017

JBA

Most information I can access is related to relatively small manually operated units and it would appear that, in addition to frequency, the amplitude of the em pulse would also be a factor in the effective depth of a unit. So it makes me wonder of a larger, vehicle mounted unit firing at higher amplitudes might be capable of deeper detecting depths.

3. Mar 5, 2017

.Scott

It has as much to do with the ground as the detection equipment. Seasat was able to image features in the Mojave Desert that were 2 meters below the surface. (http://geology.gsapubs.org/content/12/6/346). The Columbia space shuttle was able to penetrate up to 16 feet of sand in the Sahara. (http://www.nytimes.com/1982/11/26/us/spacecraft-detects-sahara-s-buried-past.html) also using SAR. In contrast, a centimeter of lead would stop superman and any SAR.

The technologies that can look the deepest and gravitational and seismic/acoustic. If you Google "reflection seismology", you will find material. See. for example. ftp://geom.geometrics.com/pub/seismic/Literature/S-TR68.pdf, a 1988 paper. Today, there are heavy trucks that can perform seismic imaging as they drive

4. Mar 5, 2017

JBA

I am aware of the seismic systems and considered the application of that technology; but, I have not seen instances of its use for shallower detection of artifacts as opposed to its common usage in deeper geophysical applications.

5. Mar 5, 2017

Staff: Mentor

Interesting question.

Gravity detection would depend on the quantity of missing mass. You might be able to detect a 100 m diameter tunnel whose roof is 100m below the surface, but not a 2 m diameter tunnel at the same depth.

I would think that seismic methods, analogous to what they use for oil exploration, could work. But it would sure upset the neighbors.

6. Mar 6, 2017

Staff: Mentor

We need to remove about 1400 kg at 100 meter distance to get a 10-12 deviation in the gravitational acceleration, the sensitivity of good relative gravimeters. If nothing else changes, a tunnel at that depth (created by simply removing material) is certainly notable. A tunnel large enough for humans at any reasonable depth would be notable.

7. Mar 6, 2017

FTM1000

radar technology will get better at detecting things like tunnels at deeper depts and different types of ground in the future or radar technology is simply limited to certain depts and ground types?

Last edited by a moderator: May 8, 2017
8. Mar 6, 2017

.Scott

The important aspects of Radar technology that may help in tunnel detection are the expansion of available radar bands and the improvements in radar signal processing. In the former case, the technology will allow processing at shorter wave lengths - but that's not likely to help with soil penetration where specific longer wavelengths seem to be best. Improvements in signal processing result from faster, more powerful computers and DSPs. You can eek out more information from a signal with better processing. But that won't buy you anything if your tunnel is a few feet beneath a bog - because there isn't going to be any signal to process.

9. Mar 6, 2017

Staff: Mentor

10. Mar 6, 2017

sophiecentaur

Bearing in mind that no tunnel would be built at extreme depth and that it has to be four or five metres in diameter at least. Its image would subtend I significant angle. I would have thought that archeological surveying methods would be suitable. A tunnel would be a hollow object so you could expect a significant Total Internal Reflection of seismic waves (?) and the missing mass would produce a measurable gravitational anomaly(?).

11. Mar 6, 2017

JBA

The type of smuggling tunnels that the border patrol is dealing with along the southern US border tend to be more of a tall narrow rectangular configuration and on the order of 1.5 meters in width.

12. Mar 6, 2017

Staff: Mentor

See above: The sensitivity of the best gravimeters is easily sufficient to see the difference. I don't know how much they cost and how challenging it would be to constantly monitor the whole border, however.

13. Mar 6, 2017

Staff: Mentor

Wikipedia says that those gravimeters need a very stable platform. A device that thumps the ground might be able to defeat any gravimeter for miles around. Ditto for an eccentric rotating mass bolted to the ground. They need only create a $10^{-12}$ disturbance to mask the tunnel anomaly.

The same question needs to be aasked about any technology because bad guys can employ clever people too. What countermeasures are possible?

14. Mar 6, 2017

Staff: Mentor

Seismic activity can disturb the gravimeters, but that is an indication of activity on its own.

You could dig a larger tunnel and fill a part of it with a high-density material. It would make the tunnel completely invisible to gravimeters. It would require a huge amount of iron or similar high-density materials, however. Simply rearranging material on the surface could also disturb measurements, but how do you do that without getting attention?

A clever arrangement of tunnel structures could mask the tunnel in terms of seismic waves (seismic metamaterial) - but that is even more complex.

15. Mar 6, 2017

Drakkith

Staff Emeritus
It looks to me like the real factor here isn't whether the technology exists to detect these tunnels, but whether the technology exists to search a potentially enormous geographical area for tunnels at a reasonable cost and within a reasonable amount of time. A ground penetrating radar that could be swept across an area dozens of meters across from an aircraft would be seem to be ideal, whereas gravimeters that can only detect a small area directly underneath them, and which require time to move, set up, and tear down would be entirely infeasible.

16. Mar 7, 2017

sophiecentaur

You would have an advantage in that the tunnels, by definition, would be passing underneath the borderline. Also. tunnels are hard work to build and the routes would probably follow straight(ash) lines which would be near perpendicular to the border. Also, a capable geologist would know the areas through which tunnelling is easier or too hard.
But I think we are getting into the realms of politics and warfare here (real world). This may be an interesting practical problem but there is a question of whether or not we should support the Israelis of the Palestinians with our 'advice'. I think I will stop contributing on this thread.

17. Mar 7, 2017

FTM1000

i am sure there is enough highly educated people in israel who works on this kind of stuff. this thread is just for me to know about the problems and future of tunnel detection technology.

18. Mar 7, 2017

sophiecentaur

I'm sorry. It is a sensitive issue with me, although I agree it is an interesting topic.

19. Nov 4, 2017

Pdgenoa

The technology is still in its infancy so it takes a long time to image but muon tomography is perfect for this kind of use.
It's likely to find many uses so the tech should eventually be refined for faster scanning.

20. Nov 4, 2017

Staff: Mentor

For muon tomography you need a detector below your measurement volume. Digging a hole every 200 meters that is well below the depth of potential tunnels doesn’t look like a feasible solution.

The speed is limited by the natural muon rate and the size of your detector. Apart from building a larger detector there is not much you can do. Portable muon sources might be possible in the future with plasma wakefield acceleration.

21. Nov 4, 2017

Staff: Mentor

How deep is the water table at these locations?

22. Nov 4, 2017