radar tracking behavior
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Trying to reconcile how the BMS radar works when a target’s radar return weakens or disappears - specifically the bolded parts of these statements:
From: http://falcon.blu3wolf.com/Docs/Electronic-Warfare-Fundamentals.pdf
h. Track coast is used to counter chaff, clutter, multiple targets, range gate stealers, jam fades, and blinking jamming by placing tracking radar in a rate-aided coast condition. The system “estimates” target position to avoid interrupting the fire control solution. A lock-on or return to acquisition mode terminates the track coast condition. Track coast requires adequate storage of rate-aided information, and no true tracking information will be developed while track coast is operating.From BMS manual -34:
A radar track will start degrading if the radar doesn’t pick it up again within a reasonable (pattern dependent) time frame. If the radar has not detected the tracked target lately (for example in the last 5 paints where the beam passes over the target aircraft but doesn’t get a strong enough return) and the radar is coasting (4 seconds since the last actual hit) extrapolation continues. After the coast time the symbol will flash to indicate imminent loss of track status; sometimes you won’t see this depending on where the target was in the scan pattern. In this situation the track will disappear unless you get a paint and detection almost immediately.and also is this regarding the same radar behavior or something else:
http://ffw08.weebly.com/uploads/3/0/4/7/30476526/radar_air-to-air_modes.pdf“rate-aided information” sounds like it’s referring to several measurements of the target’s recent changes in acceleration - so is this why there’s the ambiguous line about “a reasonable pattern dependent time frame” in the -34?
Thanks!
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All of this is dependent on what your radar scan settings are - i.e.; size of scan volume, number of bars, where end of bar/frame happens, strength of return, etc. It’s not simple, and it’s probably not even modeled in the “complete” sense in BMS, but is close enough.
You have to supplement the BMS docs to get a complete picture, and that will make BMS more understandable. If you want to know more about how radars actually work, look for texts on RL radar - Stimson’s “Introduction to Airborne Radar” is probably one of the best.
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@Stevie I see, thank you for the help and the resource there!
Do you know how BMS radars simulate the notch? Just look at the target’s aspect angle and as it gets close to perpendicular it automatically throws you into extrapolation/ coast, and if the target exits the beam w/in 13 seconds you’re good, if it doesn’t it’s lost? Or is ground clutter actually factored in? -
@AWmk1 - it sounds as if they model the actual physics. But different radars also may do different things to deal with this sort of defensive reaction, so if the BMS devs have done extensive homework one shouldn’t expect all radars to behave identically.
My guess would be that the Viper radar model has some sort of basis in available performance statistics…which doesn’t mean it’s 100% “truth”, but it’s a “good enough” model for our purposes.
What you really need to understand is just how to counter a bogey that goes into the notch - you can learn more about this from studying real radar theory. Learn the general theory first, then apply it.
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@Stevie tried a little test against hostile AI - look down vs look up: look down seems to result in beaming targets coasting and look up doesn’t…? Not sure though because they seem reluctant to beam for very long when I’m down low.
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@AWmk1 - when you fly low you trade altitude for ability to maneuver. To be “in the notch” requires a beaming maneuver by definition…and the target doesn’t have to “stay” in the notch - he only has to be there long enough to defeat an incoming shot (provided he’s not being shot with a heater - in that case the notch means nothing). So that could be a very short time, again depends on geometry.
Also - a beaming target will almost never climb…another reason why working low robs ability to maneuver. From both of you.
Another good reference is “Fighter Combat: Tactics and Maneuvering”, by Robert Shaw. I’m told that at one time this used to be a Top Gun textbook, but you can get it from Amazon now. I’ve read it cover to cover…worth it.
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@Stevie
Ok I think I see why I still notice target tracks entering coast even though I’m lower alt than them:
"Mainlobe ReturnMainlobe return—or mainlobe clutter (MLC) as it is called when it is not desired—is produced whenever the mainlobe intercepts the ground, as when looking down or flying at low altitudes and not looking up. It may be received from long ranges, even when flying at high altitudes and looking straight ahead.
Because the ground area intercepted by the mainlobe can be extensive and the gain of the mainlobe is high, mainlobe return is generally quite strong—far stronger than the return from any aircraft."
and even though it might not be a lookdown shootdown situation, the beaming target might still get lost in a distant but strong return from mainlobe clutter.
So even though I doubt mainlobe clutter is simulated and detected in BMS, I guess it makes sense that a beaming target somewhat higher alt than you can notch you?
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@Stevie there are a bunch of references to velocity gates in the -34 as if BMS does simulate these,
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@AWmk1 - again, you have to understand how a RL radar works to make some sense of this - start with how a radar bins hits using a scheme called “Barker Coding”…you won’t find any of this in the BMS docs - but BMS “behaves” in accord.
When a target beams it halts doppler velocity return - so the radar should enter coast - clutter or not - until that return is recovered. Then further geometry factors - if the bogey properly executes a notch maneuver, he will no longer be in your main beam. Which is why flying low robs (both of you) defensive ability. Notching is a 3D maneuver when properly executed…so again, your scan settings and how/when your radar updates factor (end of Bar or end of Frame) - AND how any defensive ECM in use by the bogey impacts - also factor.
…and don’t believe everything BMS has to say about AIM-120.
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@Stevie thanks - I’ve been skimming Stimson’s book which has helped.