“It’s really hard to find tiny wires in the dirt,” said General Meigs in his final JIEDDO press conference last November. “And it’s hard to find an IED that’s buried. Those are tough challenges from a laws-of-physics perspective.”
Tough, but maybe not impossible. Dozens of advanced-tech projects are aimed at detecting buried IEDs. Some systems are intended to fly aboard drone aircraft, others to be carried on vehicles; still others are to be carried by a soldier. In the airborne category are advanced imaging systems that would find buried IEDs, pressure switches, and even command wires by detecting disturbed earth. These systems, being developed by several defense contractors, would sense radiation in dozens of narrow spectral bands in the visible and infrared parts of the spectrum.
The principle is that disturbed earth scatters radiation differently from undisturbed earth. The system, called a hyperspectral imager, would run algorithms to calculate the signal strength in those spectral bands. That data would be used to map, for a grid of points on the ground, the reflectance as a function of wavelength. Limited processing power forces a tradeoff between the spatial resolution on the ground (you want to be able to see command wires) and the spectral resolution (you need a certain minimum number of spectral bands to reliably detect disturbed earth). The systems being tested now use bright, contrasting colors to show subtle differences in reflectance.
Another project, now being tested, detects command wires using a radio transmitter, carried by a soldier, that sweeps through a wide band of frequencies. The waves are polarized, and when the polarization is properly aligned with a length of buried wire, the radio-frequency energy couples into the wire. That coupling causes a resonance at a specific frequency. The system detects that resonance, which can indicate not only the presence of the wire but also its approximate length.
Troops are also testing detection systems that use ground-penetrating radar or other technologies to detect command wires. JIEDDO has publicly identified two such projects, code-named Desert Owl and Copperhead, but has not released any details.
There is also a lot of work on systems that can detect IEDs at what are called standoff distances: tens of meters, or far enough to survive if the IED blows up. A couple of years ago troops in Iraq were reportedly using a system called PING, which emitted microwave signals that penetrated building walls. If the signals encountered an IED with large amounts of metal, the IED altered those signals in a way that could be detected, presumably with reasonable consistency.
Some of these standoff systems depend, or will depend, on radically new technologies, such as terahertz-frequency and millimeter-wave radiation [see Web-only sidebar “Terahertz Waves: No Silver Bullet”], or on radical applications of existing technology. Several have already been deployed, with limited success, but most are more than a few years away. The existing technologies include visible light lasers, ground-penetrating radar, synthetic-aperture radar, thermal imaging, magnetic resonance, and electronic “sniffers” that can detect in the air infinitesimal concentrations of molecules from explosives.
A sniffer called Fido is being used in Iraq and Afghanistan; there’s a handheld version and also one attached to a small robot. Fido exploits a kind of material called an amplifying fluorescent polymer. A polymer is a long chain of identical molecular links called monomers. When a photon hits a fluorescent polymer, it releases an excited electron that travels along the chain, causing the monomers to fluoresce. The monomers are designed, however, so that if any one of them encounters and binds with a certain molecule—let’s say one from a nitroaromatic explosive—the fluorescence is quenched.
Because the chain has so many potential receptor sites, the system based on it can detect concentrations down in the parts-per-quadrillion range, according to the original paper on the invention, which was published in the June 2001 IEEE Transactions on Geoscience and Remote Sensing . But although the Fido system works well, it does so only for a limited number of explosives, according to an official familiar with it. And the only standoff capability you get is from the robot.
