How do they determine enemy aircraft type with radar?

[MrOmnos]

How do you determine if it's a  Su-30/ Mig 29/F-15/F-18 or any other aircraft for that matter using a radar?

[ataradov]

How do you determine if it's a  Su-30/ Mig 29/F-15/F-18 or any other aircraft for that matter using a radar?

All aircraft have very distinctive effective reflection surface pattern. If you know direction of travel and distance to the aircraft, you know the effective reflective surface in that direction, by observing it from multiple points, you can figure out the type, or at least get a good estimate.

That does not take into account any sort of active friend-foe detection systems, of course.

Here is Wikipedia article https://en.wikipedia.org/wiki/Radar_cross-section

[MrOmnos]

How do you determine if it's a  Su-30/ Mig 29/F-15/F-18 or any other aircraft for that matter using a radar?

All aircraft have very distinctive effective reflection surface pattern. If you know direction of travel and distance to the aircraft, you know the effective reflective surface in that direction, by observing it from multiple points, you can figure out the type, or at least get a good estimate.

That does not take into account any sort of active friend-foe detection systems, of course.

Here is Wikipedia article https://en.wikipedia.org/wiki/Radar_cross-section

I know about radar cross section. But there are lots of aircraft that are of similar size and similar in construction. It might be difficult to determine a specific aircraft by just looking at it's RCS. I was wondering how effective and accurate is this method?

[ataradov]

I was wondering how effective and accurate is this method?

Not at all. But you can also factor in cruising speed, type and speed of maneuvers it performs. It is not much, but in many cases this is all you can get. Especially in actual war situation.

In normal life, aircraft don't limit their intentional radiation, so you can detect on-board radar type, type of radio used for communication. This all goes away in a combat radio-silence mode, of course.

[saturation]

The actual systems used by different armed forces is generically called IFF.

https://en.wikipedia.org/wiki/Identification_friend_or_foe

[setq]

The planes have a little chat and your one asks another one if it is a good guy and if so, prove it. If the other one has no proof it's the bad guy.

How the conversation takes place and what defines proof depends on the IFF mode. Early systems were pretty shit and you could spoof them easily.

Taking this further, identifying what the target is takes place elsewhere and is communicated usually. They fly in high altitude airborne standoff radar to track assets on the ground and in the air. These use heuristics to define target types. Also ground based mobile radar are used. It's difficult to identify anything using RCS so range, cruise speed, previous arena state are all processed real time and mixed up with intelligence to provide a consistent picture.

That's all in an ideal world though; most of it is finger in the air shit and defence budgets being pissed away on crap.

[Kjelt]

They have multiwave radars now but actually they still can't determine that much I guess.
If you build a one square meter aluminium foil kite or balloon and let it up over 150m you get military visitors  checking it out and those are not moving at jetfighter speeds

[MrOmnos]

The actual systems used by different armed forces is generically called IFF.

https://en.wikipedia.org/wiki/Identification_friend_or_foe

You miss understood my question. IFF only identifies friendlies not foes.

[SeanB]

Most of the time there is a direction it came from, altitude and speed, so this allows you to know, from previous intel, which airport it took off from, and thus you know, from intel, what operates out there and thus what it is. Then you can either use a manned intercept or a missile to take it out if needed, or just keep it under observation until it crosses some imaginary boundary and becomes a target.

No major computer that can ID it, just a radar and commercial transponder to disambiguate commercial traffic, which should not be in a contested airspace at all, so you either have an armed escort making sure the errant commercial follows you to a designated landing spot, or it is warned off by comms on the international common frequency, and if it does not leave it becomes a target.

Standard ATC in that case is "Flight 7777, you are entering contested airspace, please turn to heading 270 and withdraw", which is invariably followed with the answer" Flight 7777, turning around". If no reply there will be 2 fully armed interceptors  flying 10m from his cockpit within 5 minutes. At night they will be on full afterburner and full speed brake, so he will see the massive flame if the radio is off. Ignore for 2 minutes one will be upside down on top of the cockpit looking in to see the pilot, and after another 5 minutes of no reply and no visible reaction from the cockpit it will be escalated and somebody will give the final disposition order.

If it is not commercial it will have the 2 interceptors, and they will enquire what is the other doing in this airspace, and if there is any problem then it is going to be handled by the other 3 standoff aircraft flying 10 000feet above and behind.

Radar control enables you to see it take off, climb to altitude and then scramble 3 interceptors. They take off ( hot standby) and climb out at max power to fl600, dropping tanks as they go empty, then they are vectored onto the target vector. they then dive at max safe velocity till within missile range, and then either fire locked on heat seeker missiles at the unsuspecting target, or blow holes in it at close range with a 20mm cannon, then whip past at full speed and try to avoid hitting the ground. Then return to base and reload, and put the new paint silhouette on the side of the cockpit. Other guy knew nothing till bullets hit him, or a missile ran up the rear and detonated. If lucky he pulled the handle and was able to eject, or dug a hole with the plane.

[MrOmnos]

They have multiwave radars now but actually they still can't determine that much I guess.
If you build a one square meter aluminium foil kite or balloon and let it up over 150m you get military visitors  checking it out and those are not moving at jetfighter speeds

High, was preparing for my antenna and propagation exams and was wondering if the refractive index gradient caused by the shock waves of  modern supersonic aircraft can be used to bend the EM waves and detect it's presence by using some kind antenna array. It would be great for detecting modern stealth fighters which have very low RCS. Every aircraft has a unique shockwave so it would bend the EM radiation in a unique way. You could tell what kind of aircraft it is.

[Len]

You miss understood my question. IFF only identifies friendlies not foes.

Well, there's the rub. It has never been an exact science.

If your military IFF transponder doesn’t get a valid response, the aircraft is a possible enemy. So what next? That depends other factors that make you believe the aircraft is hostile or not.

In the Vietnam War, for example, the usual rules of engagement for U.S. fighter pilots was that they had to actually see an "enemy" aircraft to determine if it was friend or foe, before shooting at it. Even though they had fancy IFF & radar systems that could target an enemy 20 miles away. That’s because there were several different air forces flying in from different directions, and the IFF wasn’t 100% reliable.

Here’s another example of how people can screw up even when the radar and IFF work properly.

[janoc]

You miss understood my question. IFF only identifies friendlies not foes.

Well, there's the rub. It has never been an exact science.

If your military IFF transponder doesn’t get a valid response, the aircraft is a possible enemy. So what next? That depends other factors that make you believe the aircraft is hostile or not.

In the Vietnam War, for example, the usual rules of engagement for U.S. fighter pilots was that they had to actually see an "enemy" aircraft to determine if it was friend or foe, before shooting at it. Even though they had fancy IFF & radar systems that could target an enemy 20 miles away. That’s because there were several different air forces flying in from different directions, and the IFF wasn’t 100% reliable.

Here’s another example of how people can screw up even when the radar and IFF work properly.

Also the infamous Patriot friendly fire incidents:
https://en.wikipedia.org/wiki/MIM-104_Patriot

Generally speaking, in peacetime if the radar target is unidentified (no transponder reply to radar interrogation, no radio contact, no IFF designator), the jets are scrambled and sent to have a look what the deal up there is.

It could be a passenger plane with a pilot asleep at the controls (happens more often than you would want to believe), perhaps they have screwed up the ATC handover and tuned to a wrong frequency losing contact, perhaps the pilot messed up the transponder code ("squawk") + there are a few special ones, like 7500 indicating a hijacking, maybe the plane has a technical problem ... 

Then there are those military planes of some countries intentionally flying without transponders and forcing scrambles ...

[Kjelt]

They have multiwave radars now but actually they still can't determine that much I guess.
If you build a one square meter aluminium foil kite or balloon and let it up over 150m you get military visitors  checking it out and those are not moving at jetfighter speeds

High, was preparing for my antenna and propagation exams and was wondering if the refractive index gradient caused by the shock waves of  modern supersonic aircraft can be used to bend the EM waves and detect it's presence by using some kind antenna array. It would be great for detecting modern stealth fighters which have very low RCS. Every aircraft has a unique shockwave so it would bend the EM radiation in a unique way. You could tell what kind of aircraft it is.

That is above my comprehension  wouldn,t the shockwave of the engine be different upon acceleration or steady flight ? I guess each jetengine would have its unique pattern, experienced planespotters can hear and identify planes on sound.

[vk6zgo]

You miss understood my question. IFF only identifies friendlies not foes.

Well, there's the rub. It has never been an exact science.

If your military IFF transponder doesn’t get a valid response, the aircraft is a possible enemy. So what next? That depends other factors that make you believe the aircraft is hostile or not.

In the Vietnam War, for example, the usual rules of engagement for U.S. fighter pilots was that they had to actually see an "enemy" aircraft to determine if it was friend or foe, before shooting at it. Even though they had fancy IFF & radar systems that could target an enemy 20 miles away. That’s because there were several different air forces flying in from different directions, and the IFF wasn’t 100% reliable.

Here’s another example of how people can screw up even when the radar and IFF work properly.

During the Vietnam War,a number of US aircraft decided it was really good idea to attack a New Zealand destroyer .
The New Zealanders  tried everything from the Radio,to Aldis Lamps,to signal flags to show they were on the same side,but the planes pressed home their attack.

When some of the crew were injured,the Kiwis decided it wasn't fun any more & shot back.
The Yanks apparently then noticed the NZ flag on the masthead,& went away!

[System Error Message]

radar has advanced more that its not only about detecting and seeing the speed and range, with an array you can detect shapes to some extent and that can help with identifying. You can also identify a unit by the EM signature from its own radar type to whichever other equipment it has. This sort of detection is complicated though. What most are interested in is, is that radar blip a friend? If it isnt friendly nor commercial than find  out its speed and range and intercept with missiles. If this was spying rather than combat than identifying what units and all the details is something more important than just seeing a blip and blasting it out of the sky.

Radar is also used for detecting surface things like ships as it is used to compute their range and speed to aim the guns.

[LabSpokane]

Aircraft radars can actually count the number of turbine blades in another aircraft's engine. That's one definitive clue in a/c identification.

[wasyoungonce]

Honestly...flying around with radar in transmit is not wise.   It's akin to shining a torch on the front line at nigh...everyone can see you way before you see them.    Most fighters are interdicted with AWACS or ground based radar to behind the incoming (or to good firing solutions) then when in a good position set radar to xmit targeting.  By then its way too late for the target and you minimize your exposure to enemy.

Also the radar targeting frequencies and pulses are way different to other modes.

[Jeroen3]

Radar systems don't work with a snapshot anymore. From the moment they notice an object, they start tracking and gathering information.
One of the most complicated radar stuff is not the RF itself, but the capacity to track objects. 1 object is easy, 100 objects is more difficult. Especially if they don't ID themselves.
And there are a lot of objects in the air, since radar radius is huge nowadays. Several hundred km.

The DSP is difficult, but the big data processing is even worse.