DARPA to build nothingness detector for tunnel sniffing
Bottom falls out of subterranean-lair market
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Renowned US military tech bureau DARPA has issued a request for an ultrasensitive gravity-measuring instrument which could be mounted in a low flying aircraft and detect underground tunnels.
The project, known as Gravity Anomaly for Tunnel Exposure (GATE), was formally announced on Friday. In essence, it will detect an absence of underground mass - dirt, rock or whatever - by picking out the tiny drop in the local gravity caused by the missing stuff:
The explicit action of digging tunnels introduces a void into the subsurface geology. Gravity gradiometers measure tiny spatial variations in the pull of gravity caused by these underground voids. The GATE objective is to develop, integrate, and demonstrate a prototype airborne gravity gradiometer system which is capable of detecting the mass deficit of a void in the presence of geological and topological variability.
A nothingness detector, in other words, able to perceive the hole rather than the doughnut. But in this case the wacky research agency seems to believe that the current state of the art in gradiometer systems is close to being discriminating enough to do the job already. What's needed is the ability to tune out all the noise and clutter from natural geological features, the carrying aircraft's vibration and so forth.
"This is not expected to be a sensor technology development activity, but rather focus on adapting the existing technology to GATE application," says the solicitation document (pdf).
DARPA thinks that it should be possible to fit a ground-penetrating grav spyeye and all necessary processing on board the carrying aircraft, which can be manned or unmanned. There shouldn't be any need to pipe massive amounts of sensor data back to a ground station for analysis, either. The final prototype, according to the solicitation, should offer "the ability to detect the presence of a tunnel" and "the ability to image skeletal outline of a tunnel network".
As to what you might use the GATE tunnel-sniffer gear for, DARPA does offer a hint:
To address the more immediate underground tactical threats, the Gravity Anomaly for Tunnel Exposure program will focus on border and perimeter breaching tunnels.
There have been a few border-breaching tunnels in the news lately, as it happens. ®
COMMENTS
Further note
Looks like the Hughes thingy was a g radiometer, rather than an absolute value device.
So putting one of these on each wing-tip, nose and tail flying over a tunnel should give a definite (but small?) dip across at least one pair.
Flying at constant height above ground would probably be a very good idea so terrain following radar is likely to be on board (unless you want to do post flight data reduction based on some kind of recorded ground profile) and some fairly decent vibration isolation. Foam and shock absorbers might do it but probably some kind of active system to null out aircraft movement.
Somehow though it's just not up to DARPA's usual standard. There's none of the usual crazy-as-as&*thouse-rat-with-rabies but if its even 20% there it'll be pretty impressive quality.
OTOH if it were to be artillery launched
completely nuts
Look at the amount of work put into the Goce orbiter, which is working at a much coarser level and only has to deal with drag from the outer edge of the atmosphere. These guys want something that can measure the gravitational effect (or lack thereof) of a couple hundred kilograms, somehow stabilized against surface-level winds and vibrations from the aircraft's engine. It's not going to happen.
What about the pithy DARPA description?
Whenever I encounter a new Lewis Page article mentioning DARPA, I immediately click through to find his latest description of the military boffins (eg "the military research bureau so far beyond the bleeding edge it serves moon-on-a-stick as canapés.").
But alas, it seems as if he's run out of pithy metaphors.
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