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Does the aim-120 ignore ground clutter?


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3 hours ago, Coxy_99 said:

IR missiles i understand they go for the heat, But why should active missiles ignore ground clutter if your on the ground, Or am i missing something?

 

Its quite simple the radar is what's called a pulse doppler radar:

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Additionally techniques such as range gatting also help in the matter:

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A visual of the above can be seen in the F14 when it has a pulse lock and the target is separated from the terrain:

image.png

Just imagine the range gate cuts everything out not within a small range (often measured in the low double digit meters to high single digit iirc) of the target.


Edited by nighthawk2174
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6 hours ago, nighthawk2174 said:

  

 

Its quite simple the radar is what's called a pulse doppler radar:

image.png

Additionally techniques such as range gatting also help in the matter:

image.png

 

A visual of the above can be seen in the F14 when it has a pulse lock and the target is separated from the terrain:

image.png

Just imagine the range gate cuts everything out not within a small range (often measured in the low double digit meters to high single digit iirc) of the target.

 

Yes, but there is some speed range that the radar expects when separating the target from the ground, right?

 

I mean if your closure speed drops outside this range, the radar will loose track.

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8 hours ago, Oceandar said:

You know the rule Coxy, without a track you're not going anywhere.

4 hour track replays are borked so thats never going to happen ill see if i can dig the tacview. @nighthawk2174 No was not an f14 firing on me was a 16 or 18. If the bandit is some 40nm up at 35k surely that 120 would go dead hows it possible to see you? I know the aim54 does also. I thought ground clutter was a thing.

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Just now, Coxy_99 said:

4 hour track replays are borked so thats never going to happen ill see if i can dig the tacview. @nighthawk2174 No was not an f14 firing on me was a 16 or 18. If the bandit is some 40nm up at 35k surely that 120 would go dead hows it possible to see you? I know the aim54 does also. I thought ground clutter was a thing.

Yes ground clutter is a thing but it doesn't cause you too loose lock more so it reduces detection range.   Its impact on active missiles is not immense.  Let's say the ground clutter knocks off 10% of the detection range.  For a radar lets say the amraam can see an F15 sized target at ~15NMi.  That's only 1.5NMi reduction in detection range, which in the case above wouldn't have any impact if the missile goes active at 10Nmi.

2 minutes ago, Cmptohocah said:

Yes, but there is some speed range that the radar expects when separating the target from the ground, right?

 

I mean if your closure speed drops outside this range, the radar will loose track.

Yes part of the doppler filtering process is that doppler returns below a certain threshold are dropped.  But this doesn't preclude the use of range gating both can work together to filter out noise and false targets. 

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In simple terms:

  • Aircraft AND ground closure within speed gate, ground outside of range gate: lock unaffected
  • Ground closure outside of speed gate, aircraft AND ground within range gate: lock unaffected
  • Aircraft AND ground closure within speed gate AND range gate:  now we're getting into possible lock-affecting territory

 

Note that the more advanced a radar is (F-16, F-18) the better the filtering is. As a result, the gates get smaller as radars get more advanced.

Where an F-14 radar might have a range gate of a couple hundres of feet and a speed gate of tens of knots, the F-16 radar might reduce this to a couple tens of feet and a couple knots.

 

Furthermore, as @nighthawk2174 mentions: as the missile gets closer, the radar return from your aircraft gets stronger. As a result, the gates get even smaller. Within 5-10 miles, your radar return might be so powerful that there's physically no way to hide it from the sensor (which is where electronic warfare comes into the picture).

 

Think of it like tossing a metal object into a forest at night, and shining a flashlight in the direction you tossed it. The closer you get, the stronger the reflection will become and the more the metal plate will stand out amidst the twigs, leaves and stones.

 

Only the speed-gate is partially simulated within DCS.

 


Edited by Noctrach
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14 hours ago, Coxy_99 said:

IR missiles i understand they go for the heat, But why should active missiles ignore ground clutter if your on the ground, Or am i missing something?

 

They ignore it as long as you're out of the notch, yes.  Even if you're in notch it may not be good enough because there are techniques that digital sensors can use to basically 'not care', and in some cases even analog ones can do this - it has to do with SNR which has to do with how far away the missile is from the target vs. the ground in terms of the LOS.  That last part isn't modeled in DCS; and as far as AMRAAM goes, it switches to MPRF IRL which further reduces clutter problems for it.

 

In DCS, it was set up to continue flying and looking towards where a target notched, then people complained and ED 'fixed the fix' ... but really IMHO this should have been applied to other missiles also instead of being reverted.

 

This is different from IR because the IR missile does not illuminate the target, and therefore the intensity of the signal coming back from the ground is much greater, and the target can actively work to reduce its IR signature as well.  The IR wavelength being homed in on also matters in terms of the source - it's very different from an engine compared to the skin, and only the more modern missiles can see both - in DCS those would be all-aspect missiles - but the atmosphere eats a LOT of IR already, and combine it with a hot earth ... SNR drops.

 

 

4 hours ago, Coxy_99 said:

4 hour track replays are borked so thats never going to happen ill see if i can dig the tacview. @nighthawk2174 No was not an f14 firing on me was a 16 or 18. If the bandit is some 40nm up at 35k surely that 120 would go dead hows it possible to see you? I know the aim54 does also. I thought ground clutter was a thing.

 

If you don't take the time to reproduce with a short track, ED won't take the time to debug.  You know this.


Edited by GGTharos
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Bugs exist to get reported.

 

Besides, I feel it might be a difficult reality for people to accept that real world missiles and radars, if anything, are a lot better than they are in DCS.

Kinda the result of missiles in DCS being a scripted object in a game that players use to shoot down other players in a manner that's somewhat believable.

You're processing one projectile in a huge simulation, where the real deal is using all its available processing capacity just to hit the thing it's supposed to hit.

 

This is why DCS is a fun experience where you can push the limits of what the simulation can do, while real life is both terrifying and boring because all your tactics revolve around coming home in one piece.

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35 minutes ago, GGTharos said:

 

They ignore it as long as you're out of the notch, yes.  Even if you're in notch it may not be good enough because there are techniques that digital sensors can use to basically 'not care', and in some cases even analog ones can do this - it has to do with SNR which has to do with how far away the missile is from the target vs. the ground in terms of the LOS.  That last part isn't modeled in DCS; and as far as AMRAAM goes, it switches to MPRF IRL which further reduces clutter problems for it.

 

This is especially silly when there is no ground clutter within the effective range of the missile's radar. i.e shallow look down angles (< 15 degrees) with a target around 20kft agl or above notching an active missile is just stupid, the ground clutter at this point would be pretty much negligible since the slant range to the ground is huge.


Edited by 104th_Blaze
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Anecdotal though it may be, I once had a mate's 120C go active on me (in a Ka-50) unintentionally while he was engaging a MiG-23. We were playing on the Syria map, and at the time I was quite literally hovering below the height of surrounding buildings, stationary in some courtyard (Had been like that long before the missile was even launched). Never the less, the missile track was spot on, and ended up impacting the corner of a nearby building which stood between me and it.

 

Was enough to take out both engines and perhaps make me a little saltier than I'd have liked.

 

Now, for what I've gathered here and there on these forums is that helicopter rotors are supposed stand out like a sore thumb to radar; but I also understand (correct me if I'm wrong) that's not how DCS currently works.

 

My question is, would it be within the realms of possibility for an AMRAAM to pick up a stationary helicopter a few tens of kilometres away in a courtyard, hovering at ~2m alt, amongst the busy background of a sizable town?
 

If the answer is yes, then what kind of effect would heavy road traffic have on the track? since technically any vehicle would provide some kind of doppler contrast.

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1 hour ago, Cheetah7798 said:

Now, for what I've gathered here and there on these forums is that helicopter rotors are supposed stand out like a sore thumb to radar; but I also understand (correct me if I'm wrong) that's not how DCS currently works.

 

My question is, would it be within the realms of possibility for an AMRAAM to pick up a stationary helicopter a few tens of kilometres away in a courtyard, hovering at ~2m alt, amongst the busy background of a sizable town?
 

If the answer is yes, then what kind of effect would heavy road traffic have on the track? since technically any vehicle would provide some kind of doppler contrast.

 

The answer to the first question is yes, thought with the caveat that the doppler shift of multiple large blades advancing and retreating simultaneously generates an effect similar to noise jamming and was a huge challenge for radars in the 80s. Modern radars have filtering techniques to work around this to varying degrees (and AESA is black magic).

 

For the second question, this is exactly why doppler gates exist, particularly in air-to-air search modes. Traffic moving along the highway with 80+ kph, trees moving in the wind, it all generates a noticeable doppler shift. The point that @GGTharos, @nighthawk2174, others and myself try to make in threads like these is that this kind of filtering immediately shifts once a target is locked.

 

Once you've verified that the signal you are receiving is not noise (i.e. when you commit to a lock), you can close your range and doppler gates to exclude everything that's not your target. The variables you are left to compensate for are target acceleration, closure and range. All the rest is the physics of wavelength.

 

Air-to-ground mode in Hornets and Vipers will be able to see and lock traffic moving on the highway, because it's not filtering/compensating in the same way air-to-air modes do. Heck, you can try this in the Tomcat right now with MLC off. 😉 But once a target is locked, it'd have to be flying at the same speed and within a couple hundred feet to get highway traffic into the signal gates.

 

 


Edited by Noctrach

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39 minutes ago, Coxy_99 said:

No idea i was not in a chopper but plane. So there was no moving parts as such.

 

Your own aircraft is still moving relative to the stationary object, so its radar is still detecting a doppler shift. While this signal is unlikely to be very far above surrounding noise levels, a metal airframe will absolutely give a stronger doppler reflection than an airfield tarmac or bunch of shrubberies. Air-to-ground radar can distinguish stationary vehicles from surrounding forest thanks to this. It's again the analogy of the metal object in the brush. It will just provide a stronger reflection, which can be filtered out of the surrounding noise.

 

It's unlikely a radar would do this in air-to-air mode because it'd be looking for different things. But it's by no means impossible.


Edited by Noctrach

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As far as DCS is concerned though Coxy is exactly right, those 120s should not be hitting stationary targets on the ground.  Heli rotors (any rotors) moving at speed would be an exception, but DCS doesn't do that either.

 

Technically they could lock onto the engine JEM line but that would be really grasping for straws, especially since missiles are programmed to reject those and most importantly...no LOS.

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1 hour ago, GGTharos said:

As far as DCS is concerned though Coxy is exactly right, those 120s should not be hitting stationary targets on the ground.  Heli rotors (any rotors) moving at speed would be an exception, but DCS doesn't do that either.

 

Technically they could lock onto the engine JEM line but that would be really grasping for straws, especially since missiles are programmed to reject those and most importantly...no LOS.

 

Thank you on the server earlier same thing from F-16 lobbing 120s at me on the ground, I have no tracks because there borked 😞 Anything over 2 hours 😞  Ive never known this before, Like i say i dont know but its worth testing.

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More importantly you don't have the shooter's track, so ED wouldn't be able to debug at all.  This is why, what you need to do is create a little mission where you try to recreate this scenario exactly.  Your plan, the other plane, start at more or less the right distance and try to replicate.

 

I wonder if there was some lag (you appeared to lag to the other guy) which would have caused you to be a blip on his radar, thus letting him shoot you ... this is why I'm saying the track from both ends is necessary.

 

Try the ground radar too, might be surprised there.


Edited by GGTharos

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