Will Stealth Survive As Sensors Improve?

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For the last 30 years stealth technology on planes and ships has brought battleground advantage to the world's leading military powers. Countries like the United States have been able to fly undetected on missions into Iraq, Serbia, Afghanistan, and Iraq (again) to deliver precision strikes to enemy targets. However, new radar technology could render stealth technology obsolete.

Cassidian, part of the massive Europe-wide European Aeronautic Defence and Space Company (EADS), has developed a kind of "passive radar" which it claims can detect stealth aircraft. Passive radar detects radiation signals emitted by other sources -- be they radio broadcasts or mobile phone networks -- and analyses distortions to figure out where objects are located.

Stealth technology conventionally works by minimising the reflective profile of an object, with perhaps the most famous example being the iconic triangular-ish Northrop Grumman B-2 Spirit bomber. Conventional radar systems emit signals which then "bounce" off objects, giving away their location (exactly how a bat "see" in the dark using noise) -- the B-2's shape, wide and shallow with perpendicular surfaces, absorbs those signals (or reflects them away from any detector) to avoid revealing its presence.

The system Cassidian proposes, however, wouldn't be fooled by standard stealth cloaking techniques because it takes advantage of a range of signals which surround us constantly. There's no need to fire out signals and look for their reflections -- instead, the detector system looks at a host of signals floating in the atmosphere already (like aforementioned radio and mobile phone signals) and looks for how they're blocked or altered by having to pass through or around objects. Triangulating several different sources can build up a picture of a landscape or airspace, with stealth planes and ships just as visible as everything else.

Even more worrying for commanders, too, is that because passive radar stations don't emit anything, there's no way to track them down. The tactic of sending in a stealth bomber to take out enemy radar capabilities before sending in the conventional planes wouldn't work -- passive radar detectors can be small and spread out over a large area.

Cassidian also claims that passive radar has applications for civilian air traffic control. Simpler, smaller passive radar stations will be cheaper and easier to set up and maintain than the current systems used at airports around the world. A prototype of the system is currently being tested at Stuttgart Airport, and if it works as well as hoped then we could see it begin to appear at other airports within a couple of years.

Passive radar has started to look like an effective tool in smaller-scale situations -- Wired.co.uk reported on the development of tech that can detect people through walls using the Wi-Fi and other signals that permeate human settlements. It could have a use in a hostage situation (where the police need to know where the bad guys are inside a sealed room), or the fire service could use it to locate people within buildings filled with smoke.

'Passive radar' could render stealth planes obsolete (Wired UK)

 

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The 'unjammable' quantum radar that could render ALL stealth planes useless

State of the art jamming technology sends back 'spoof' signals that fool radar operators into believing their target is harmless or elsewhere
New technology can detect these kinds of ruses by reading the quantum signature of photons transmitted to ensure the signal is genuine
Any attempt to measure a photon always changes its quantum properties

U.S. researchers have employed the quantum properties of photons to create an unjammable radar signal.

Conventional radar is vulnerable to a range of technologies, ranging from dropping chaff to create false reflections to drowning the radar frequency with noise.

More sophisticated radar can deal with such ploys, but the most sophisticated radar jammers are able to intercept the the signals and send back false information.

However, a team from the University of Rochester, New York have shown how the quantum properties of photons can be used to outsmart this advanced stealth technology.

The new radar concept relies on the fact that any attempt to measure a photon always destroys its quantum properties, MIT's Technology Review explains.

To exploit this curious property, the Rochester team suggest using polarised photons to detect and image objects.

If a stealth aircraft attempts to intercept these photons and resend them in a way that disguises its position, it would inevitably change the photons' quantum properties - revealing any interference.

'In order to jam our imaging system, the object must disturb the delicate quantum state of the imaging photons, thus introducing statistical errors that reveal its activity,' the researchers say in a paper published in the journal Applied Physics Letters.

Schematic of the quantum-secured radar: If a stealth aircraft attempts to intercept the photons and resend them in a way that disguises its position, it would inevitably change the photons' quantum properties

The technology works in a similar way to quantum key distribution for cryptography, where any eavesdropper would change the quantum properties of the key by listening in, revealing his or her presence.

Mehul Malik, who led the team that carried out the research at Rochester's Institute of Optics, tested the concept by bouncing photons off a stealth bomber-shaped target and measuring the return signal's polarisation error rate.

The system easily imaged the war plane without any eavesdropping, but when the adversary intercepted the signal and modified it to send back the image of a bird, the radar was easily able to see through the ruse.

No fooling us: When there is no jamming attack, the received image faithfully reproduces the actual object, shown left. If the target attempts to send a 'spoof' image like the one on the right, the imaging system can detect the presence of the jamming attack, because of the large error rate in the received polarization

'That's an impressive demonstration of the first imaging system that is unjammable thanks to quantum mechanics,' says MIT Technology Review's Physics arXiv blog.
'A sophisticated jammer may use quantum teleportation to teleport the polarisation state of our querying photons onto photons carrying false position or time information'

However, the researchers admit that their novel radar system is still not perfect. As MIT's blogger explains, it suffers from the same limitations that plagued early quantum cryptographic systems.

The quantum radar sends photons in pulses that contain several of the quantum particles, one or more of which could be easily siphoned away and replicated to tune the signal sent back to the same state as the one sent.

'Further, a sophisticated jammer may use quantum teleportation to teleport the polarisation state of our querying photons onto photons carrying false position or time information,' says the study.

However, while the equipment needed to carry out such sophisticated jamming is readily available in labs worldwide, it is not thought yet to be deployed by the military.

Read more: The 'unjammable' quantum radar that could make the present generation of stealth technology obsolete | Daily Mail Online
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