Review
Review
Can stealth aircraft be detected optically?
10Dagon
3Yair Halberstadt
3antanaclasis
8ssq
2Yair Halberstadt
8avturchin
2Yair Halberstadt
2avturchin
2Yair Halberstadt
2avturchin
2Yair Halberstadt
2avturchin
2Yair Halberstadt
2avturchin
2avturchin
2Yair Halberstadt
2Yair Halberstadt
2avturchin
2Yair Halberstadt
2Linch
1Dave5
1osten
9Alexander Gietelink Oldenziel
3faul_sname
4Yair Halberstadt
1Exa Watson
2sapphire
2Yair Halberstadt
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6 Answers sorted by
101
Wild guesses here. I've done work in optical product identification, but I don't know how well those challenges translate. Also, it's an obvious enough idea that I expect there are teams working on it.
Lens and CCD technology is not trivial at those speeds and insane angular resolution. It's not just about counting pixels, it's about how to get light to the exact right place on the sensor, for long enough to register. I honestly don't know if that's solvable.
More boringly, clouds and nighttime would make this much less useful, especially as enemies can plan missions around the expected detection capabilities. I haven't done the math, but even on clear days in daytime, dust and haze likely interfere too much for even a few KM distance.
Lens and CCD technology is not trivial at those speeds and insane angular resolution.
But we can easily capture a picture of a fighter jet when it's close. And the further it is the higher the angular resolution required, but also the lower the angular speed, so do those cancel out to make it not much harder, or it doesn't work like that?
3
You can’t just trivially scale up the angular resolution by bolting more sensors together (or similar methods). It gets more difficult to engineer the lenses and sensors to meet super-high specs.
And aside from that, the problem behaves nonlinearly with the amount of atmosphere between you and the plane. Each bit of distortion in the air along the way will combine, potentially pretty harshly limiting how far away you can get any useful image. This may be able to be worked around with AI to reconstruct from highly distorted images, but it’s far from trivial on the face of it.
80
There are some important factors you've missed that provide clues as to why systems like this don't already exist and invalidate stealth investments.
The short answer is no, because the Koschmieder limit for an F35 sized target is much shorter than that which you propose. A system broadly as you describe will (empirically) detect a target with an apparent size roughly half to three-quarters the size of an F35 (frontal aspect - the only one you should care about for a defence system) from about 6km away (6.3+/- 1.3km). The limiting factors on this are principally optical, and aren't trivially solvable by just adding more pixels.
The longer answer. A 100km distant target has 100km of air between it and you as well, which will emit light (of approximately the same color as the background sky by day), absorb light (from the target) and disort light from the target. Distortions are in the order of multiple arc minutes (for targets that present at about 5 arcminutes in the best case aspect from a distance of 15km). The image you show is the highest contrast and angular resolution case you are likely to find (target at largest aspect and fully silhouetted against the sky), and also probably the most recognisable aspect as well. The visible band offers very poor contrast for this use case, and that is the main reason why IR dominates search and track despite its cost and limitations (because aircraft emit strongly in IR, which helps immensely to push up the SNR and signal to bakcground). Additionally, you must account for loss of information due to the system's own optics.
Systems such as you envisage already exist, but not generally exclusively in the visible band. Fused EO and IRST search and track systems exist, but their practical ranges are far, far shorter than either you envisage or RADAR functions, against fighters. EO search and track has been in use for tracking and gun laying, including AA guns, since the 1970s and predates IR.
80
That is why they prefer to flight for strikes during moonless nights. Also they can fly of very low or very high, which makes optical observation difficult.
Aircraft already often fly low, which also works well against radar, but makes them vulnerable to cheaper and more numerous MANPADS. Flying high shouldn't work particularly well given the setup I've described here, since we have a range of about 100km, an order of magnitude higher than the f35 can fly.
2
Flying very low, like 10-30 meters above the ground in night will protect against even MANPADS - it will fly above you in a few seconds.
I recommend an interesting blog https://xxtomcooperxx.substack.com/p/its-the-range-stupid-part-1 which discuss a lot about air defence and current war
2
But then no need for stealth at all?
2
They likely use them in places where no air defence is present and still at some disatnce using JDAM.
I think that I missed the main thing about stealth - they are stealth for radar on the distances like 100 km, but visible for radar on the distances like 10 km (arbitrary numbers). But optical observation on distances of 100 km is impossible (need large telescopes, but you need to know where to look). Also optical density of atmosphere starts playing role as well a spherical size of earth.
2
Why would you need large telescopes?
Naked eye has angular resolution of 30m at 100km, you need something slightly better. A small lense should do it. Cameras + zoom lens are well understood mass produced components. And this is a highly parallelizable task.
2
Did you ever see any plane that far? I saw only planes above me (10 km) and they are almost like dots.
The difference between optics and radar is that with optics you need to know where to look - but the radar has constant 360 perception.
2
But I discussed that in the post. All you need are enough cameras + processing power. Both are cheap.
2
Also, radars are good in pinpointing exact coordinates in space and time. Optical recognition may have delays or difficultly in measuring distance. Even 1 second delay makes their information useless for supersonic aircrafts.
2
It works only if it fly above your territory - and similar systems are used for drones detection now. Actually, they use people eyes and smartphones and instant messaging. But during recent attack on Iran a single F35 flied over Iraq and fired a missile from like 200 km distance on a target in Iran.
2
Note you don't even need high resolution in all directions, just high enough to see whether it's worth zooming in/switching to a better camera.
Night is an obvious point! Should have thought of that!
Still this is relevant when the stealth aircraft is providing tactical support, rather than bombing operations, when you can't necessarily pick the time to provide aerial support. But tactical support is usually from behind the front lines, rather than over enemy territory, where anti aircraft weapons are less effective anyway.
2
Tactical support aircraft are not stealth like A-10 but can be used only if airdefence is supressed
2
I wasn't referring to the A10, but the use of e.g. f-35s in ground support roles - as heavily practised by the IDF for example.
20
Traditionally spy aircrafts fly at night, exactly for this reason. I suppose you could also paint them sky-blue for camouflage but I think empirically "flying at night" and being grey-black is the historical strategy that they've chosen.
10
Clouds are a thing.
110
Two complications perhaps?: Earth surface curvature + hills, does it work at night?
Military nerds correct me if I'm wrong but I think the answer might be the following. I'm not a pilot etc etc.
Stealth can be a bit of a misleading term. F35 aren't actually 'stealth aircraft' - they are low-observable aircraft. You can detect F35s with longwave radar.
The problem isn't knowing that there is a F35 but to get a weapon -grade lock on it. This is much harder and your grainy gpt-interpreted photo isn't close to enough for a missile I think. You mentioned this already as a possibility.
The Ukrainians pioneered something similar for audio which is used to detect missiles & drones entering Ukrainian airspace.
Let's rephrase: if this was a major issue for the f-35, the USA wouldn't have invested trillions of dollars in stealth without addressing optical camouflaging. All f-35s would have camouflage paint. They'd be a lot of research into how to reduce visibility of aircraft, just like there is for reducing RCS. Given they don't do this, clearly they don't think optical detection is a major concern.
Related question - Can you link me a summary of why aircraft weapons are good. I feel like it should be kinda hard to hit an aicraft with a missle or whatever. Aicraft are moving really fast and are not the biggest target. How much faster are missiles? The jet is already moving at a high speed but the missle has to accelerate from zero. Aircraft seem pretty vulnerable to lasers but are those kind of defenses actually deployed at our current tech level?
You're intuition is correct when the jet has already passed ahead - those are very hard to catch and shoot down. But usually you detect an aircraft when it's heading towards you, and all the missile has to do is intercept. It doesn't even have to be faster than the jet (unless the jet detected it in time and does a 180).
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