Jump to content

Radar performance changes based on target aspect even with identical closure velocity


Arctic Fox

Recommended Posts

When attempting to detect and track radar contacts, radar performance seems to differ drastically depending on whether the target is presenting its tail or nose to your aircraft, even with identical parameters and in particular identical closure rate.

I set up a test with a B-52 flying towards and away with me with my aircraft and the target at different airspeeds to bring the closure rate in line: In the tail chase scenario, with a Vc of 550 knots, the target was not detected until 50 miles and STT could not be acquired until 34 miles. When the target is hot, it can be detected at ranges in excess of 85 miles and I successfully managed to track it at 77 miles even with a much lower Vc of 470 knots.

Additionally, it seems that the behaviour of the radar in different PRF modes is also inconsistent with target aspect. When attempting to detect the cold target, MPRF picked up the target at ranges exceeding those at which HPRF could pick it up: https://gfycat.com/incomparableunconsciouskoi

When targeting the closing target, MPRF could not achieve STT at ranges where HPRF acquired instantly, even at a lower Vc: https://gfycat.com/powerfulenormoushamadryad

Tracks for both tests are attached.

I'm guessing all of this might apply to the F-16 as well, but I haven't tested it.

Cold Target.trk Hot Target.trk

  • Like 6
  • Thanks 5
Link to comment
Share on other sites

As far as I know DCS will divide an object's aspect into 4 quarters (hot/beam/cold) for the purposes of things like the chaff/flare random% to decoy so I wonder if that's also happening here.

This current behavior doesn't much much sense to me, the aspect of a target should be irrelevant to a radar except for a change in presented geometry and thus likely RCS. Which as far as I am aware, RCS in DCS is static so this wouldn't be the case.

This could potentially also be part of the culprit for why notching in DCS is overtuned, its possible it is taking into account the beam quarter instead of/or in addition to closure.

Anyway, I'm just speculating as to the cause, great find!

 1A100.png?format=1500w  

Virtual CVW-8 - The mission of Virtual Carrier Air Wing EIGHT is to provide its members with an organization committed to presenting an authentic representation of U.S. Navy Carrier Air Wing operations in training and combat environments based on the real world experience of its real fighter pilots, air intercept controllers, airbosses, and many others.

 

Link to comment
Share on other sites

On 5/12/2022 at 12:35 AM, MARLAN_ said:

As far as I know DCS will divide an object's aspect into 4 quarters (hot/beam/cold) for the purposes of things like the chaff/flare random% to decoy so I wonder if that's also happening here.

This current behavior doesn't much much sense to me, the aspect of a target should be irrelevant to a radar except for a change in presented geometry and thus likely RCS. Which as far as I am aware, RCS in DCS is static so this wouldn't be the case.

This could potentially also be part of the culprit for why notching in DCS is overtuned, its possible it is taking into account the beam quarter instead of/or in addition to closure.

Anyway, I'm just speculating as to the cause, great find!

RCS is static in DCS

Link to comment
Share on other sites

  • 2 weeks later...
  • 3 weeks later...

Has there been any development on the investigation of this issue? @BIGNEWY/@NineLine

 1A100.png?format=1500w  

Virtual CVW-8 - The mission of Virtual Carrier Air Wing EIGHT is to provide its members with an organization committed to presenting an authentic representation of U.S. Navy Carrier Air Wing operations in training and combat environments based on the real world experience of its real fighter pilots, air intercept controllers, airbosses, and many others.

 

Link to comment
Share on other sites

Aspect does matter for detection with Doppler, because it's not just your closure rate to the target that makes it stand out, but the difference in the closure rate to the target and the ground. The radar knows your own jet's ground speed, and it's comparing that with the returns it gets back from both the ground and the target. A hot return with 400 knots closure is going to stand out more than a cold return with 400 knots closure, because it's a lot more if a difference vs the background terrain returns.



Sent from my Pixel 3 XL using Tapatalk

  • Like 1

Dances, PhD

Jet Hobo

https://v65th.wordpress.com/

Link to comment
Share on other sites

3 hours ago, TheBigTatanka said:

Aspect does matter for detection with Doppler, because it's not just your closure rate to the target that makes it stand out, but the difference in the closure rate to the target and the ground. The radar knows your own jet's ground speed, and it's comparing that with the returns it gets back from both the ground and the target. A hot return with 400 knots closure is going to stand out more than a cold return with 400 knots closure, because it's a lot more if a difference vs the background terrain returns.



Sent from my Pixel 3 XL using Tapatalk
 

Just thinking in text here, I'm no radar expert.

1) Ownship 200 kts, target 200 kts, hot, 400 Vc. Closure to ground 200 kts. Difference between target and ground 200 kts.

2) Ownship 600 kts, target 200 kts, cold, 400 Vc. Closure to ground 600 kts. Difference between target and ground 200 kts.

Isn't this the same?

Also hopefully ED can make RCS at least partly dynamic because generally showing your tail or beam quarter increases your presented RCS which would negate some of the gains by reducing your closure to the radar.

 

  • Like 4

 1A100.png?format=1500w  

Virtual CVW-8 - The mission of Virtual Carrier Air Wing EIGHT is to provide its members with an organization committed to presenting an authentic representation of U.S. Navy Carrier Air Wing operations in training and combat environments based on the real world experience of its real fighter pilots, air intercept controllers, airbosses, and many others.

 

Link to comment
Share on other sites

Indeed. If:

  • closure velocity = (own velocity + target velocity) for a hot target
  • closure velocity = (own velocity - target velocity) for a cold target
  • ground velocity = (own velocity)

Then simple math will show you that if the closure rate is the same, it does not matter whether the target is hot or cold. The difference between the relative velocity of the background clutter and the relative velocity of the target is the same. I'm pretty sure in the tests I did here there was even a higher difference with the cold target.

Ultimately this is not how a radar works anyway. If you're well outside the various blind velocities of the radar then the detection range does not scale with closure velocity like that, especially not to this magnitude (and as it happens a target that is close to the beam is typically the easiest to detect due to increased RCS, though DCS does not generally simulate that). Also these tests were done in look-up over water so this is doubly irrelevant.

  • Like 4
Link to comment
Share on other sites

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...