reported AIM-120C losing targets easily for chaff even at close ranges

[Cmptohocah]

3 minutes ago, GGTharos said:

Correct, there was never any effect on the aircraft's own radar in DCS.   The thread is about the 120 though - in the end that's the explosive delivery dart.

 

You can expect chaff to have zero effect on aircraft radars until ED decides otherwise, and, frankly, until radar cells and a whole host of things around radar cells are simulated, chaff effects on aircraft radar will probably be poor, if any.

Would it make any sense to implement something simple like:

If target closure below some value and chaff is there, roll die and then snap radar to fake target for x amount of seconds?

After that repeat.

[SgtPappy]

55 minutes ago, GGTharos said:

I would argue that a constant release of chaff might move the centroid behind the aircraft smoothly.  But, I don't actually know that.

 

This is what I'm thinking as well and some texts support that this the case but none explicitly prove it. The research continues

[GGTharos]

45 minutes ago, Cmptohocah said:

Would it make any sense to implement something simple like:

If target closure below some value and chaff is there, roll die and then snap radar to fake target for x amount of seconds?

After that repeat.

 

No, it doesn't even really make sense for missiles but it is what we have.   It's possible that chaff may behave like this in some specific situation (like gun-tracking distance maybe?) but beyond this everything is about radar cells.

And it's easily defeated with rate gates as well - given that pretty much almost every radar we have available in DCS (Except MiG-21 and F-5) builds a target track, I suspect chaff decoying a locked target would be very unlikely in most cases.  The reality is that this would probably work with maneuvers but there's no way to represent this just with rolling a die.

 

It has other utilities for which you still need radar cell simulation - also, in the case of look up, right now we remove the clutter filter and with chaff showing up maybe you need that notch gate again.

 

All IMHO.

Edited March 30, 2021 by GGTharos

[SerialCaveman]

46 minutes ago, GGTharos said:

I would argue that a constant release of chaff might move the centroid behind the aircraft smoothly.  But, I don't actually know that.

And I would fully agree. However, it is not the behaviour that we observe in game. Switch is not gradual, but abrupt and generates very sharp maneuver of the missile.

 

34 minutes ago, Cmptohocah said:

Would it make any sense to implement something simple like:

If target closure below some value and chaff is there, roll die and then snap radar to fake target for x amount of seconds?

After that repeat.

I would slightly modify: If target closure below some value and chaff is there AND chaff is moving no slower than -  for example - 50 m/s than aircraft, roll die and then snap radar to fake target. for x amount of seconds?

Then no repeat, I don't think that missile would require. If it was given information from launching aircraft radar, it wouldn't have gone for chaff in the first place.

[GGTharos]

There's no chaff motion in DCS - it may move with the wind but basically it's at 0 speed the moment it exits the aircraft, there's no boom time and it exists for only 5 seconds.

But maybe if you force a brief search (simulating a break-lock) instead of transfer to chaff that would be interesting.

Edited March 30, 2021 by GGTharos

[nighthawk2174]

8 minutes ago, SerialCaveman said:

Then no repeat, I don't think that missile would require. If it was given information from launching aircraft radar, it wouldn't have gone for chaff in the first place.

The missile should be able to reacquire so long as the target is still in its fov once the chaff is dropped out due to doppler.  Assuming it beat all the other methods of filtering it would still eventually fall below the doppler speed.  As such once this happens if the target is detected in a search pattern (could the amraam reacquire from the radars sidelobes if close enough?) I see no reason it wouldn't start tracking again.  For the amraam if its getting datalink updates it should continue tracking on the datalinked target so long as it gets updates.  From what's out there the missile will drop contacts in favor of what the datalink is pointing too.

Edited March 30, 2021 by nighthawk2174

[Cmptohocah]

I guess I didn't explain correctly, what I actually meant.

Since it was mentioned that the intricacies of the entire radar-chaff system, by radar I mean launching aircraft's, are difficult to model and current effects in DCS on them are non existent, would it make sense to model the effect chaff would have on the fore mentioned radar?

 

For example: closure rate of the target is small enough to cause some potential issues with the target track. Target releases chaff and for some predefined time period the radar has difficulties tracking the original target. More chaff released, more "snapping" happens - radar alternates between the real target and the chaff.  Would that be acceptable approximation of what happens in RL?

Some die roll would simulate a bit of randomness, so not all of the released chaff would cause tracking issues.
 

Edited March 30, 2021 by Cmptohocah
Fixed bad writting

[SerialCaveman]

28 minutes ago, nighthawk2174 said:

The missile should be able to reacquire so long as the target is still in its fov once the chaff is dropped out due to doppler.  Assuming it beat all the other methods of filtering it would still eventually fall below the doppler speed.  As such once this happens if the target is detected in a search pattern (could the amraam reacquire from the radars sidelobes if close enough?) I see no reason it wouldn't start tracking again.  For the amraam if its getting datalink updates it should continue tracking on the datalinked target so long as it gets updates.  From what's out there the missile will drop contacts in favor of what the datalink is pointing too.

 

I was talking only on scenario when missile is notched and target is releasing chaff - so that chaff stays in doppler gates for a long time. Then, after it went to chaff, there's no turning back - after few seconds target would have flown outside of missile beam, besides - missile would have moved its doppler gete to match chaff. At least if you track chaff, be good at it and don't go for random airplane!

 

I think that when missile is not notched and can reject chaff based on doppler - it will, tending towards maximum closure rate for head - on, and minimum when tail-on, thus rejecting chaff in nearly 100% of cases.

 

I also think that - in presence of Kalman, and also accurate enough on-board INS - it is no-brainer to make filter that takes both carrier aircraft AND on-board radar data, smashes it together, and provides target trajectory estimation more accurate than otherwise possible. Also it further increases ECCM capibility and reduces chance of switching to wrong target.

Edited March 30, 2021 by SerialCaveman
Clarification

[GGTharos]

5 minutes ago, Cmptohocah said:

I guess I didn't explain correctly, what I actually meant.

Since it was mentioned that the intricacies of the entire radar-chaff system, by radar I mean launching aircraft's, are difficult to model and current effects in DCS on them are non existent, would it make sense to model the effect chaff would have on the fore mentioned radar?

 

For example: closure rate of the target is small enough to cause some potential issues with the target track. Target releases chaff and for some predefined time period the radar has difficulties tracking the original target. More chaff released, more "snapping" happens - radar alternates between the real target and the chaff.  Would that be acceptable approximation of what happens in RL?

Some die roll would simulate a bit of randomness, so not all of the released chaff would cause tracking issues.

 

 

Why not?  At the same time, look at the complaints that there are for radar operation already ... so yes, all of it is nice and all of it has a whole bunch of barriers

3 minutes ago, SerialCaveman said:

I was talking only on scenario when missile is notched and target is releasing chaff - so that chaff stays in doppler gates for a long time. Then, after it went to chaff, there's no turning back - after few seconds target would have flown outside of missile beam, besides - missile would have moved its doppler gete to match chaff. At least if you track chaff, be good at it and don't go for random airplane!

 

You're more likely to pick up a random airplane if it's there though, IMHO - this is why you don't shoot missiles into a furball.   In DCS because the missile tracks a specific game object ID, SARH are 'safe' but they should be every bit as bad as ARH about it.

[nighthawk2174]

8 minutes ago, SerialCaveman said:

I was talking only on scenario when missile is notched and target is releasing chaff - so that chaff stays in doppler gates for a long time. Then, after it went to chaff, there's no turning back - after few seconds target would have flown outside of missile beam, besides - missile would have moved its doppler gete to match chaff. At least if you track chaff, be good at it and don't go for random airplane!

 

I think that when missile is not notched and can reject chaff based on doppler - it will, tending towards maximum closure rate for head - on, and minimum when tail-on, thus rejecting chaff.

 

I also think that - in presence of Kalman, and also accurate enough on-board INS - it is no-brainer to make filter that takes both carrier aircraft AND on-board radar data, smashes it together, and provides target trajectory estimation more accurate than otherwise possible. Also it further increases ECCM capibility and reduces chance of switching to wrong target.

Not to mention range gating, edge tracking, the monopulses ability to discern between multiple target in its res cell,  and the fact that chaff will slow down very very very quickly.  Kalman filtering would be nice to see for sure, so would a lot of the stuff were talking about.

[SerialCaveman]

16 minutes ago, Cmptohocah said:

I guess I didn't explain correctly, what I actually meant.

Since it was mentioned that the intricacies of the entire radar-chaff system, by radar I mean launching aircraft's, are difficult to model and current effects in DCS on them are non existent, would it make sense to model the effect chaff would have on the fore mentioned radar?

 

For example: closure rate of the target is small enough to cause some potential issues with the target track. Target releases chaff and for some predefined time period the radar has difficulties tracking the original target. More chaff released, more "snapping" happens - radar alternates between the real target and the chaff.  Would that be acceptable approximation of what happens in RL?

Some die roll would simulate a bit of randomness, so not all of the released chaff would cause tracking issues.
 

 

I don't think that any jerking movements of missile seeker is realistic. As far as I know (not a radar specialist!), when presented with two- target problem, monopulse solution will tend to point somewhere between, not directly at one of them.

In addition to, because seeker antenna angular rate is (gross simplification incoming) feed to autopilot as acceleration command, some kind of smoothing filter is added, so that noisy and erratic antenna movement doesn't translate into noisy and erratic missile trajectory - or at least, not as noisy and erratic.

 

10 minutes ago, GGTharos said:

 

 

Why not?  At the same time, look at the complaints that there are for radar operation already ... so yes, all of it is nice and all of it has a whole bunch of barriers

 

You're more likely to pick up a random airplane if it's there though, IMHO - this is why you don't shoot missiles into a furball.   In DCS because the missile tracks a specific game object ID, SARH are 'safe' but they should be every bit as bad as ARH about it.

I think that SAHR would be even worse. ARH can use a little bit more precise data, combining target position from aircraft (quite precise if radar is in STT), and own seeker data, creating better target state estimation (at least, in theory). Not implemented in DCS, as we know.

 

2 minutes ago, nighthawk2174 said:

Not to mention range gating, edge tracking, the monopulses ability to discern between multiple target in its res cell,  and the fact that chaff will slow down very very very quickly.  Kalman filtering would be nice to see for sure, so would a lot of the stuff were talking about.

Still, as far as i know, monopulse have no ability to distinguish between multiple targets in beam, if these targets somehow are not filtered out earlier based on doppler or range gate. As far as I know, only AESA radars have such theoretical ability, and I'm not even sure if it is implemented on military radars.

[nighthawk2174]

10 minutes ago, SerialCaveman said:

I don't think that any jerking movements of missile seeker is realistic. As far as I know (not a radar specialist!), when presented with two- target problem, monopulse solution will tend to point somewhere between, not directly at one of them.

In addition to, because seeker antenna angular rate is (gross simplification incoming) feed to autopilot as acceleration command, some kind of smoothing filter is added, so that noisy and erratic antenna movement doesn't translate into noisy and erratic missile trajectory - or at least, not as noisy and erratic.

 

I think that SAHR would be even worse. ARH can use a little bit more precise data, combining target position from aircraft (quite precise if radar is in STT), and own seeker data, creating better target state estimation (at least, in theory). Not implemented in DCS, as we know.

 

Still, as far as i know, monopulse have no ability to distinguish between multiple targets in beam, if these targets somehow are not filtered out earlier based on doppler or range gate. As far as I know, only AESA radars have such theoretical ability, and I'm not even sure if it is implemented on military radars.

I have a book purely dedicated to monopulse radars and there is a section on the ability to distinguish between multiple targets in the beam. I don’t remember the specifics but I do remember it being possible to a certain extent.

[SerialCaveman]

Monopulse Principles and Techniques?

 

It seems like I was wrong and you were right. But, resolving correct target is valid for low number of targets (two target case was presented, and seems rather easy in theory), with ideal radar and with reduced tracking accuracy. With increasing amount of targets it becomes impossible, with 10-20% chance of breaking a lock completely off whole cluster of targets.

 

However, it seems relatively easy to implement functionality, that recognizes multiple targets in beam and invalidates monopulse solution. That should prevent seeker antenna (and also a missile) from going haywire. I would rather expect it to go (literally) ballistic in direction of previously predicted impact point, until valid target is reacquired.

 

Outside of this book, i found also few much fresher articles, that I had no time to thoroughly read and understand - but it seems that whole matter is more complicated than we might think.

[SgtPappy]

Monopulse Processing for Tracking Unresolved Targets by W. D. Blair published by the USN's Naval Surface Research Center in 1997 goes into using the complex/quadrature measurements for monopulse signals as mentioned earlier. So far, I haven't heard of any other monopulse technique in other articles other than using this portion of the signal. I haven't completed the whole thing yet but a brief excerpt here so far suggests that there still is some difficulty in tracking a given target when there's more than one in the res cell, especially if the RCS fluctuates as it would for a maneuvering target. 

 

Figure 1.3 shows two closely-spaced helicopters moving apart in both x and y dimensions (top down view) and the resulting in-phase signals stop fluctuating wildly and manage to find the accurate position of each chopper. As they move apart and time passes, the quadrature signal starts to fluctuate from the initial value of 0 for target 1 (since AFAIK, when it sees the targets as one, there is no quadrature return) - suggesting the presence of multiple targets. Tracking one over the other is another matter as the text below describes:

 

 

 

 

 

Edit: I should also add that reference [1.4] mentioned just above is a 1965 paper proposing resolving or achieving "at least recognition of the number of targets present". This paper is COMPLEX INDICATED ANGLES IN MONOPULSE RADAR - by S. Sherman, University of Pennsylvania.

Edited March 31, 2021 by SgtPappy

[Bear21]

There are two very similar threds on this subject, I repost what I posted there;

 

There is an open text that describes a "hypothetical A-A missile seeker " here https://digital-library.theiet.org/content/books/10.1049/sbra024e_ch18

 

I have this document, I can't publish it here as it's a pay doc. But it gives all the parameters for an A-A radar seeker of the type we discuss here, info such as angular, range, doppler gates etc and as I understand it the person who made the example knows what his is doing. It's a generic representation of how A-A radar missile seekers are made today, i.e. an AIM-120 C or D, Meteor etc, but it's information is not classified as it approximates all but describes none.

Edited April 3, 2021 by Bear21

[Bear21]

 Based on the data in the IET report (which is an excerpt from the Book "Pulse Doppler Radar by Alabaster) the missile seeker has the following values:

 

Range gate based on 4us pulse and chirp pulse compression 20m

Beam width 12° based on low Ku band seeker in 7 inch missile body (like AIM-120).

Velocity gate 7m/s based on 32 point FFT.

 

The sensitivity of such a seeker to chaff will be highly dependent on geometry, for several reasons:

 

- The range gate cuts the chaff bloom efficiently for a hot or cold target geometry (10m bloom distance before passing out of the range gate)

 

- The angle resolution is not involved in a hot or cold target but very much so for a flanking and cranking target. The angle resolution is 3000m at 8nm, 1500m/4 and 750m/2. As the target will be somewhere in the middle, the chaffs affecting distance is half this for a flanking/cranking geometry, so 1500/8, 750/4 and 375/2. The chaff has the time to bloom to a reasonable size in this distance (the time for the aircraft to leave the cell is irrelevant as the seeker follows the aircraft with it's monopulse processing, thus the chaffs working distance is around the given values).

 

- The doppler processing will attenuate the chaff, as it retards fast to the speed of the ambient air. The term ambient air is important as an aircraft creates strong vortice mats in flight. The first picture show the vortice mat created by a 1G flight of the Citation. The more G then stronger vortices, and for a straked aircraft there are more vortice trails than off the wingtips, second  picture. This shows the condensation streams = low pressure = high local velocity of the air but does not show the full extent of the vortice mat (combine picture 1 and 2).

 

What one can conclude is a hot or cold low aspect aircraft will have a low effect from emitted chaff. The radars range gate cuts the amount of chaff and the high in-effect doppler gate (closing or receding speeds are high, the 7m/s doppler bins around the target doppler are then effectively filtering out the chaff that's inside the range gate and is operating in the 7 low doppler bins (based on a maximum vortice radial speed of 50m/s).

 

A cranking aircraft turning through the flanking position achieves three things:

 

1. The resolution goes from the short range gate to the wide angle gate.

 

2. The turn creates strong vortices that have local speeds of say 0-50 m/s (anyone's guess, but this seems reasonable inside the half angle gate)

 

3. The turn forces the missiles doppler processing to follow down to the region where the vortice trapped chaff has radial speeds that fall inside the the tracking doppler bins. The missile senses the clutter situation continuously through the many digital range and doppler gates and for a non-low level intercept it's geared to a low clutter passage through zero doppler for the target. Chaff deployed as the aircraft goes from high aspect, through the flanking position and out the other side will be effective in very different manner than chaff deployed in a hot or cold geometry. It will have time to bloom before angle cut-off and it will have radial chaff speed components in the doppler bins the radar uses for tracking.

 

DCS is wise in staying away from modeling this too closely as it's sensitive stuff. But a simple model should contain a couple of parameters:

 

- The geometry when the chaff bundles are deployed, where a high aspect geometry shall increase the probability of effect. The probability of effect in low aspect geometries shall be low.

 

- The targets G when entering the high aspect shall have an effect. High G when crank through zero doppler shall increase probability of chaff effectiveness.

 

- An effects constant based on the resolution capability of the tracking radar. A missile has the angle resolution problem (the SAMs have larger dia bodies but also 2/3 to 1/2 the seeker frequencies of the A-A missiles), a fighter or SAM radar is much less affected by this problem (their beamwiths are 1/4 of the missiles).

 

 

Edited April 3, 2021 by Bear21

[BlackPixxel]

17 hours ago, Bear21 said:

DCS is wise in staying away from modeling this too closely as it's sensitive stuff. But a simple model should contain a couple of parameters:

 

- The geometry when the chaff bundles are deployed, where a high aspect geometry shall increase the probability of effect. The probability of effect in low aspect geometries shall be low.

 

 

 

This is already what DCS is doing.

 

Chaffing a missile when hot/cold is practically impossible, and the lower your radial velocity the higher the chance.

 

To a certain degree this is also modelling the range cell impact, as with radial velocities close to 0 the chaff will stay longer in the range cell.

[GGTharos]

18 hours ago, Bear21 said:

DCS is wise in staying away from modeling this too closely as it's sensitive stuff. But a simple model should contain a couple of parameters:

 

There's nothing sensitive about this.  What's sensitive is specific means of defeating countermeasures and the procedures for applying them - DCS isn't in danger of knowing those.  The only problem here is a lack of time/money to implement.

[Bear21]

7 minutes ago, GGTharos said:

 

There's nothing sensitive about this.  What's sensitive is specific means of defeating countermeasures and the procedures for applying them - DCS isn't in danger of knowing those.  The only problem here is a lack of time/money to implement.

I agree. The simple model (or something similar) I described is not sensitive. What is, is modeling specific ways different seekers and radars try to work around these fundamentals.

[GGTharos]

We don't know anything sensitive.

[Csgo GE oh yeah]

I'm beginning to think that ED intentionally 'nerfed' the aim120 hard because pressure from russia or something  .
It's not just the chaff, the whole last part of the guidance is completely bonkers. 
I've been watching a lot of tacviews and it's actually like they intentionally miss. ?
Even when there is no chaff. They will actually TRY to fly around the target , and it doesn't matter how fast they're going. Mach 2, mach 3 ... 

You only really have a shot on a slightly manouvring target from within 10 miles. 
Anything outside 10 miles means the missile trying extra hard to do something dumb. 



 

Edited April 4, 2021 by Csgo GE oh yeah

[Xhonas]

Some of you on this thread have a lot of knowledge regarding missiles. So, i'd want to ask you guys about this https://streamable.com/4xacy4 . I recorded this tacview from a fight that i had in the current patch. Is this the correct behavior for a modern ARM? Should the notch be an insta win tatic against missiles as it is right now? Me, as an enthusiast, heard that the notch isn't used by the pilots to defeat missiles, instead, it is used as a decision making moment, where you decide if you're going to recommit into the fight or if you're going to extend cold to defend an incoming missile. I've also heard that chaff is so worthless against modern ARM missile seekers that its more probably that the plane's radar gets fooled by chaff rather than the missile seeker (and even that is very unlikely to happen). I dont think that the current behavior of DCS missiles in regard to CCM / Notch resistance is right.

[dundun92]

3 hours ago, Csgo GE oh yeah said:

I'm beginning to think that ED intentionally 'nerfed' the aim120 hard because pressure from russia or something  .
It's not just the chaff, the whole last part of the guidance is completely bonkers. 
I've been watching a lot of tacviews and it's actually like they intentionally miss. ?
Even when there is no chaff. They will actually TRY to fly around the target , and it doesn't matter how fast they're going. Mach 2, mach 3 ... 

You only really have a shot on a slightly manouvring target from within 10 miles. 
Anything outside 10 miles means the missile trying extra hard to do something dumb. 



 

 

Or maybe you just dont know employ them properly?

[nighthawk2174]

7 hours ago, Csgo GE oh yeah said:

I'm beginning to think that ED intentionally 'nerfed' the aim120 hard because pressure from russia or something  .
It's not just the chaff, the whole last part of the guidance is completely bonkers. 
I've been watching a lot of tacviews and it's actually like they intentionally miss. ?
Even when there is no chaff. They will actually TRY to fly around the target , and it doesn't matter how fast they're going. Mach 2, mach 3 ... 

You only really have a shot on a slightly manouvring target from within 10 miles. 
Anything outside 10 miles means the missile trying extra hard to do something dumb. 

Like I've seen this happen but it doesn't happen as often as you make it out to be.  It is strange that they will just kind of miss for some unknown reason but I haven't managed to get a good track of it yet and it is almost certainly its own bug.

 

3 hours ago, Xhonas said:

Some of you on this thread have a lot of knowledge regarding missiles. So, i'd want to ask you guys about this https://streamable.com/4xacy4 . I recorded this tacview from a fight that i had in the current patch. Is this the correct behavior for a modern ARM? Should the notch be an insta win tatic against missiles as it is right now? Me, as an enthusiast, heard that the notch isn't used by the pilots to defeat missiles, instead, it is used as a decision making moment, where you decide if you're going to recommit into the fight or if you're going to extend cold to defend an incoming missile. I've also heard that chaff is so worthless against modern ARM missile seekers that its more probably that the plane's radar gets fooled by chaff rather than the missile seeker (and even that is very unlikely to happen). I dont think that the current behavior of DCS missiles in regard to CCM / Notch resistance is right.

If you have the original tacview file that'd help with this as well.  But what you've heard is correct i've heard as much from real pilots and various documents that are out there.  DCS right now isn't particularly accurate; chaff is essentially a flare but for radar missiles that's how you need to treat them.  With some extra factors that influence their effectiveness such as aspect.   Right now it seems that once notched/chaffed the missile is incapable of re-acquiring the target which it should be able to do.  It doesn't help when the missile will go for a chaff bundle that's already quite some distance from the target and at near 0 speed already as well.  Not to mention if your providing datalink updates it shouldn't loose the track either.  The notch is a real weakness for all PD radars.  While the amraam should have countermeasures against this it can still get notched and potentially miss.

Edited April 5, 2021 by nighthawk2174

[GGTharos]

2 hours ago, Xhonas said:

Me, as an enthusiast, heard that the notch isn't used by the pilots to defeat missiles, instead, it is used as a decision making moment, where you decide if you're going to recommit into the fight or if you're going to extend cold to defend an incoming missile.

 

You're confusing the notch, which is a specific feature/weakness of pulse-doppler radar that is generally present in all modern radars with a particular procedure for executing tactics.  'Pull to 3-9 and assess spike status' is done with enough room to out-run bandits and missiles.  It's not intended to be a specific missile-defeat maneuver - it is done at a prescribed distance from the opponent, leaving time to check if the opponent is tracking you and thus make a decision with how to proceed.

The notch is real and it will always be there for a PD radar.

 

Quote

I've also heard that chaff is so worthless against modern ARM missile seekers that its more probably that the plane's radar gets fooled by chaff rather than the missile seeker (and even that is very unlikely to happen). I dont think that the current behavior of DCS missiles in regard to CCM / Notch resistance is right.

 

None of that means anything.

Edited April 5, 2021 by GGTharos