If an IR device, such as a tracking FLIR system (not a heat-seeking missile), tracks an aircraft and that said aircraft would launch flares. Is the IR tracking device likely to be confused by the flares?

Obviously, the point of defensive flares is to decoy missiles. I want to know if other IR devices tend to be as fooled as a missile.

  • $\begingroup$ do you understand that those two are by design to work against each other? there are really great and crappy flares and IR trackers so it really depends on which particular instances you are talking about, e.g. first-gen AIM-9 missile vs the greatest countermeasure today or first-gen countermeasure with latest-gen AIM-9? $\endgroup$ – user3528438 Jul 12 '18 at 12:08
  • $\begingroup$ What makes these next-gen countermeasures superior to the old ones in fooling the missile and vice-versa? I'm assuming the answer of my question is "yes depending on the equipment used"? $\endgroup$ – Cedric Martens Jul 12 '18 at 12:20
  • $\begingroup$ yes it's pretty much like asking "is a spear likely to pierce a shield?". $\endgroup$ – user3528438 Jul 12 '18 at 12:23
  • $\begingroup$ Is it really a flare if it doesn't affect a tracker? Isn't it then just a shiny, ineffective doo-dad? :) $\endgroup$ – abelenky Jul 12 '18 at 15:05
  • $\begingroup$ I edited my question to be more precise on what I am asking. $\endgroup$ – Cedric Martens Jul 12 '18 at 20:24

I want to know if other IR devices tend to be as fooled as a missile.


Modern imaging systems are not susceptible to flares in the same fashion as older missile seekers, which is precisely why modern missiles like the ASRAAM and AIM-9X use imaging seekers.

The reason flares worked at all was due to the physical layout of early missile seekers. These used a photocell detector that was sensitive across a wide field of view, on the order of 90 degrees. The trick is how do you use a device that basically provides a "yes, there is something in front of me" to track a target down to the sub-degree precision needed to actually hit it from long range?

The common solution, the "chopper", was to point the photocell forward and place it immediately behind a spinning metal disk with rectangular slices cut out of it following the pattern of slices on a pizza. As the disk rotated, the slices would periodically line up between the target and photocell, causing the photocell to give off a brief flash of power. For instance, if the target was above the missile, the photocell would see it whenever one of the slices was oriented vertically.

The frequency of the pulses was the same as the speed of the disk's rotation. These were sent into a smoother that produced a sine-wave output that peaked, in time, where the target was located. That means that the phase of this output encodes the relative angle between the missile and the target. By comparing this signal to the signal driving the disk motor, the resulting "error signal" directly encodes the direction the missile has to turn.

Early missiles were this simple, feeding the amplified output of the sensor directly into the control surfaces. The resulting flicking motions of the controls became known as "bang-bang". This was extremely inefficient, so a number of additional tricks were used.

The main one was to adjust the motion of the controls by the "angle-off", the angle measured from the missile centerline to the target (as opposed to the angle around the missile body, like a clock). Recall that the slits are rectangular. This means that the amount of time that the signal is present, it's pulse width, is dependant on how far the target is from the center of the disk.

For a target near the center, there is an almost constant signal because the linear motion of the slit is much slower (think of a record turning) and the slits are very close together. In contrast, a target near the outside instead creates very brief flashes at a single time. By subtracting the averaged signal from the raw signal you can determine the angle-off.

So here's why flares were so effective...

For simple bang-bang systems, the flight controls would suddenly start receiving more than one signal. As the aircraft flew away from the flare, the controls would begin flicking back and forth, causing it to track to the center of the two. This not only made it miss the target, but could lead it to run out of energy due to all the drag from the constantly moving controls.

In the case of the more sophisticated sensors, which includes many early missiles like the Sidewinder, flares can be even more effective. That's because when the signal from a target at the center is evened out it goes to zero, so if the missile is tracking properly it has little signal to work with. As the flare moves away, the aircraft's signal remains low but the flare's becomes huge, drawing the missile away from the aircraft. As the missile centers on the flare its signal disappears too, but hopefully after the aircraft has exited the seeker's field of view.

Both concepts only work if the flares move away from the aircraft with some speed - they are generally useless on helicopters for instance. For these types of roles, a new system was created. This normally consisted of an electrically heated block of metal or ceramic, with a series of metal shutters in front of the block. The shutters flicked open and close, producing random flashes of IR on the seeker. This caused the guidance signals to have random peaks, causing the missiles to fly around tracking the phantom signal. Another concept uses a low-power IR laser and a scanner like the ones in a supermarket to cause the beam to periodically pass by the missile, presenting a similar random pattern.

None of these systems work against imaging systems or seekers. For one, they no longer use timing to create the control signal, but instead use a variation of contrast tracking. Hot block decoys image at the same location as the target, so they simply increase the tracking signal, precisely the opposite of what you want. Flares, in theory, can still work, but even trivially simple image recognition systems can measure the size of the IR signals and immediately reject small objects like flares. And with modern processors, one can easily calculate the speed of all of the objects and look for ones that are rapidly slowing down.

Flares still have considerable utility against man-portable and older ground-launched missiles for the simple reason that most of the ones you are likely to meet in the field, including both fSoviet and US models, use some variation of a chopper. You can also release massive numbers of flares and attempt to obscure the target when the missile is far away and it cannot resolve the flares, but that can be accounted for by tracking the release points.

Against a modern missile, flares are generally useless. This has led to the concept of a towed decoy that is essentially a small plane on a wire. These can, theoretically, fool imaging seekers, but I suspect they are not as effective as one would wish. Thus the move to longer and longer-ranged missiles, where the fight really comes down to who has the best radar - which is likely always going to be "the west".

Another approach that is seeing some interest is the use of IR lasers to dazzle the seekers. These generally use UV seekers to look for rocket motors and then scan a laser around that area. If the laser hits the missile it can blind the sensor long enough to escape. I'm not sure if any such system has been deployed.

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    $\begingroup$ Nice answer, I was just about to post a much less detailed version. But I'd contend that that flares are still not useless: they reduce the SNR the seeker head can obtain, which increases the effectiveness of other countermeasures. As for towed decoys, they're more jammers than decoys, but are a measure against RF, not IR missiles. $\endgroup$ – Therac Jul 13 '18 at 18:16

Yes that's what military aircraft are doing when they dispense strings of flares during attacks as protection from heat seeking missiles.

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In general, yes. Flares burn very hot, hence emit a large flux of IR, which reads as an alternate target for any IR sensor.

Whether the decoying is successful depends a lot more on the software in the tracker (missile head, say) -- if it's like a 1970s police speed radar, and tracks the strongest signal, any old flare hotter than the jet exhaust will pull it off the intended target. If it's programmed to ignore secondary targets once a target has been acquired, the flare has a much harder job.

There are ways to make a flare look more like the primary target, and there are more sophisticated ways to make a tracker ignore the decoy. Like the age-old war between weapons and armor, which one is ahead at any given time depends on who made a technology breakthrough, and managed to implement/deploy it, most recently. Just as radar chaff largely became obsolete in the 1970s, flares are obsolete in some ways (they don't bother radar tracking missiles at all, for instance, though there are other ways to decoy or lose those) -- and still vital in others.

Other IR systems, like FLIR, will surely detect and display the flare as an IR source, likely a brighter one than the aircraft's engine -- but since FLIR is a human-interface display technology, rather than an automatic system, whether it is "distracted" is up to the operator. A skilled FLIR operator is very unlikely to lose the primary target due to flare launch, unless a flare does a very good job of emulating the temperature and heat flux of the engine, and the engine significantly changes its signature simultaneous with the flare launch.

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