Inner workings of a Thirdwire radar

[SFP1Ace 33]

TK was kind enough to explain how the RadarSearchRange and RadarStrength parameters work in-game. This is from the topic I started over at thirdwire forums:

 

"Well, in reality, I _think_ max range is determined not only by target RCS (and return signal etc), but also by the radar's PRF (pule repetition frequency). In order to detect far away target, your radar has to wait long enough between each pulse so it doesn't send out next pulse before return from target is obtained, otherwise, it'll get "ghost" or "alias" returns resulting in incorrect range measurement. But having long wait time between pulses (low PRF) means less frequent target update, somthing not desirable when you're trying to track targets. This is why most radar has longer range for seach (with lower PRF settings), but shorter range for track (higher PRF setting).

 

(of course, modern radar may or may not be so limited, they can send two different types of pulses and modulate them and do all sort of fancy stuff with computers, but thats beyond the scope here)

 

In the game, I think the max range range setting , say at 160 NM, reflects this PRF limit, so it is the absolute max range you can detect. The radar will not detect anything at 161 NM no matter how big the target RCS is. Target with small RCS can only be detected at shorter range than max range setting.

 

I _think_ the game data is normalized so if the radar strength is at 100, it detects 10m^2 target at max range. If radar strength is less than 100, then it can only detect larger RCS than 10m^2 at max range, and if strength is higher, it can detect smaller RCS target at max range, etc.

 

TK"

 

And another one:

 

" I _think_ (I could be all wrong here ) the strength modifies the RCS required for detection at max range, so strength 100 = 10m^2, 50 = 20m^2, 25 = 40m^2, etc...

 

And the radar return signal is proportional to inverse of range^4, so the detection range is proportional to the strength^1/4. So, I think, the detection range for the same 10m^2 target would change to, based on strength, 100 = max range, 50 = 84% max range, 25 = 70%, etc... I think...

 

And again, this is "game RCS", which may or may not have any relation to the real life RCS, its calculated based on collision radius...

 

TK"

[Fubar512 1,350]

Ask TK if he's ever held a USCG radar operator's endorsement, if he's ever had to sit and sweat through the actual examination required to qualify for one (If my memory serves me right, the minimum passing grade was the same for that as it was for the rules-of-the-road portion of the exam....a "90" ). He's already confused PRF with PRI in his explanation (a common enough mistake, even wikipedia has it wrong).

 

In layman's terms: PRF is the frequency change within the pulse that is used to define a target's characteristics and movement (doppler). PRI is the actual interval between those pulses.

 

But don't take my word for it, we have quite a few military and civilian radar operators here. I'm sure that they'll chime in.

 

A figure of "100" in game has absolutely no corollary in real life. I've set in-game radars at (for example) "60", and had absolutely zero issues detecting and acquiring bomber-sized targets sporting a default RCS Modifier value, at 200 nautical miles. The flip side of this is that while a radar set at a value of "120" was able to detect a stealthy model at 17 nm, one imbued with a value of "30" was still able to detect that same model at a range of 12 nm (be my guest, perform the math for us).

 

I'm sure that TK used (some) real-world data to a degree....but as he's said on numerous occasions "Think of this series as a sim-lite"

Edited August 3, 2010 by Fubar512

[Fubar512 1,350]

Here's a better explanation for you, my friend: http://www.alphalpha.org/radar/intro_e.html

 

"When discussing about the radar range, a distinction must be made between the non-ambiguous range and the real detection range. The non-ambiguous range is (for a pulsed radar) related to the Pulse Repetition Frequency (PRF, = 1/PRI, Pulse Repetition Interval)

 

A typical radar timing is shown in fig.1: the two transmit pulses (Tx and Tx2) are divided by a time equal to the PRI. Rx1 is the echo from Tx1 reflected by a target placed at "Range A". Rx2 can be either the echo from Tx2 reflected by a target at "Range B" or from Tx1 reflected by a target at "Range C

 

In the latter case the target is said to be at ambiguous range.

 

 

Figure 1

 

A typical radar timing is shown in fig.1: the two transmit pulses (Tx and Tx2) are divided by a time equal to the PRI. Rx1 is the echo from Tx1 reflected by a target placed at "Range A". Rx2 can be either the echo from Tx2 reflected by a target at "Range B" or from Tx1 reflected by a target at "Range C".

The maximum non-ambiguous range is the one corresponding to the PRI"

[SFP1Ace 33]

Awww Fubar, you've just smashed my hopes to smithereens . " The flip side of this is that while a radar set at a value of "120" was able to detect a stealthy model at 17 nm, one imbued with a value of "30" was still able to detect that same model at a range of 12 nm (be my guest, perform the math for us).". Okay, here's the math, all according to TK's info: radarstrength=120 - detection range=17 NM. So for radarstrength=30 detection range for a same RCS target will be (30/120)^1/4=0.7; 0.7*17 nm = 11.9 NM. Sounds about right, right? So why were you able to detect bomber at max range even though you lowered signal strength to 60? Because you didn't lower it enough! :D According to TK all radars are normalised to detect 10m^2 RCS targets at max detection range (say in your case the said 200 NM) at signal strength 100. If you lowered the strength value to 60 ten max detection range dropped from 200 NM to (assuming that default strength was 100?)....(60/100)^1/4 = 0.88; 0.88*200 NM = 176 NM. So even with RadarSearchStrength at 60 you aircraft was still able detect RCS 10m^2 at 176 NM, so i don't see any problems for it to detect 100m^2 RCS B-52 bomber at slightly longer range of 200 NM :D. So far every numerical data provided by TK checked out! So what's the theoretical limit to detect this 100m^2 bomber in game? Ok (100/10)^1/4 = 1.78. The radar (in theory) would be able to detect that bomber at 1.78*200 NM = 356 NM (at RadarSearchStrength = 100). But it won't cause RadarSearchRange = 200 imposes a "hard" limit of 200 NM (what TK's written in his post). So no wonder that even though you lowered the RadarSearchStrength from (I'm assuming) 100 to 60 it still had no problem finding that bomber :) You would have to try much lower value of 10 or even 5 to see radical drop in detection range. The most importatnt information that TK has provided is that (in game) radars are normalised to detect RCS of 10m^2 at max radarsearchrange, when radarsearchstrength is set to 100! All the rest we can work out with equations. I hope I didn't bore you all to death?

 

Best Regards!!!!

 

EDIT: loads of typos

Edited August 3, 2010 by SFP1Ace

[Fubar512 1,350]

The "experiment" () I mentioned, was performed using the F-14B against the default TW Badger at 200 nm, and then, against the F-117 at 17 nm. I ramped down the Tomcat's radar search and track strengths to "60" for both tests, I believe (though I'm not sure, it was almost two years ago), that even at "60", I could see the '117 at perhaps 15 nm. Anyway, the interesting thing isn't maximum search distance...play with maximum track distances, and see what happens The results may surprise you.

[SFP1Ace 33]

I would guess that track range is the range from which you can obtain a lock and/or track targets (for avionics70 equipped aircrafts)? But I'll have to play with it to be sure :) Hmm I've just looked up F-14B data files and there's seem to be some discrepancies - in avionics.ini search and track range are 200/160 NM but in data.ini it's only 150/100??? So basically it makes your wingman and other AI F-14 be at disadvantage compared to palyers F-14 when detecting tracking targets? Is this normal of is it a mistake?

 

Anyway to me TK's explanations make sense (they allow for quite close approximations), and if we only knew how to calculate in game RCS then knowing real life detections values for given RCS (usuly from the data I found western radars are described for 5m^2 and russian radar ranges are for detecting 3m^2) for given radar, then it would be possible to mod the hell out of this game, as far as radars go!!! ;) Still I intend to tweak some radars anyway...

 

avionics.ini searchrange/searchstrength trackrange/trackstrength data.ini searchrange/searchstrength trackrange/trackstrength:

 

TW F-15_A avionics.ini - 160/200 160/150 data.ini - 160/160 80/160 - WTH??? AI F-15s have half of the tracking range of the players aircraft???

TW F-15_BAZ avionic.ini - 160/200 160/150 data.ini - 160/200 80/200 - even more confusing?

[Spinners 15,986]

Just stick some chewing gum on the windscreen and go guns!

[ArturR 17]

I'm not sure whether the values in avionics.ini are in miles... 200/160 NM is really far ~370/296 kilometers

[SFP1Ace 33]

Would Wrigley's be good enough?

[SFP1Ace 33]

I'm not sure whether the values in avionics.ini are in miles... 200/160 NM is really far ~370/296 kilometers

 

Yes, nautical miles... I think that F-15 radar is kind of awacs or something, that's totally too much. But the you've got the values slightly wrong. First one (160) is radar searchrange in nautical miles which is around 296 KM, the other value (200) is abstract radarsearchstrength value. If that value was 100 instead of 200 than it would indicate that TW F-15_A can detect targets with RCS=10m^2 at it's maximum range, and because the value is even higher (200) than it means that its able to detect even smaller targets (RCS=5m^2 I think) at its maximum range of 160 NM. And I don't think F-15A radar was THAT good, can anyone confirm/dismiss this?

Edited August 3, 2010 by SFP1Ace

[SFP1Ace 33]

avionics.ini searchrange/searchstrength trackrange/trackstrength data.ini searchrange/searchstrength trackrange/trackstrength:

 

TW F-15_A avionics.ini - 160/200 160/150 data.ini - 160/160 80/160 - WTH??? AI F-15s have half of the tracking range of the players aircraft???

TW F-15_BAZ avionic.ini - 160/200 160/150 data.ini - 160/200 80/200 - even more confusing?

 

Belay that, my fault, TK pointed me to right direction - track radar mode entry in avionics is still limited to 80 NM:

 

[RadarData]

AvailableModes=SEARCH,TWS,STT,ACM

RangeUnit=NM

RangeSetting[1]=10

RangeSetting[2]=20

RangeSetting[3]=40

RangeSetting[4]=80

RangeSetting[5]=160

RadarPosition=

MaxElevationAngle=60

MinElevationAngle=-60

MaxAzimuthAngle=60

MinAltitude=50.0

BoresightElevation=-2.0

BoresightAzimuth=0.0

MinReturn=0.01

MinimumSpeed=25.72

SearchRange=160

SearchStrength=200

TrackRange=160 - I thought this was an error

TrackStrength=150

TWSUpdateTime=0.5

AcquisitionSymbolSpeed=1.0

AcquisitionResetPosX=0.0

AcquisitionResetPosY=0.2

AcquisitionResetTime=5.0

DisplayLimitLeft=29

DisplayLimitRight=226

DisplayLimitTop=29

DisplayLimitBottom=226

StartRangeSetting=4

 

But here it seems to be allright:

 

[RadarDisplayTWS]

RangeSetting=1,2,3,4 - Range setting 4 is 80 NM so it's OK, player doesn't have an advantage over AI afterall...

BarElevation[1]=0.75

BarElevation[2]=-0.75

ScanRate=60

ScanBeamAngle=2.5

ScanArc=60

PPI=FALSE

[+Dave 2,322]

Just stick some chewing gum on the windscreen and go guns!

 

 

Right on Spinners, right on!

[JediMaster 451]

IIRC, talking about the new AESA radars for the F-15C "Golden Eagles" an article mentioned it would effectively double the range at which they could detect (not track, that wasn't mentioned) fighter-sized targets. That longer range was quoted as about 80 miles, implying the standard F-15C radar can only see fighters out to about 40 miles. This makes a lot of sense as to why AWACS are needed, because if F-15s really could see out 200 miles all the time they'd need AWACS a lot less! They can see bombers farther out, of course, but really as the radar outranges its longest-range weapons (AMRAAM and Sparrow), how much farther does it need to see them anyway?

The main benefit to the F-15's AESA upgrade (as well as the Super Hornet and standard on the F-22 and F-35) will be the ability to detect cruise missiles at low level at ranges that will allow them to run a good intercept. Against a theoretical stealthy opponent of course it would help as well, but only to a point. Seeing a target is the first step to destroying it, but it's only the first step. Tracking it is next and that's what stealthy planes have proven most difficult to do. Then even if you CAN track it, if the missiles can't maintain a lock until you get very close to the target, you risk the target knocking you down long before you can hit them, the old brought-a-gun-to-an-ICBM-fight problem.

If the AMRAAM goes active too far away from a stealthy target to see it, can the launching aircraft continue to provide steering cues until it can, or is that no longer an option?

[SFP1Ace 33]

Right guys I guess I seem to be obsessed with things I can't get out of SF2 engine because there are many unknown variables that TK won't, can't, or just doesn't remember to share. And that just makes me even more obsesive, like a pitbull fixated on a target, LOL. Yeah, I'll just follow your (subliminaly suggested) advice and stick the chewing gum in that special place and go guns (read - have a cold bear, relax, and let the radar stuff in the hands of TK - what else did you think ? ). Afterall why should I bother to study mysteries of SF2 engine? It's such a waste of time, right?

 

But in the end I still believe that info TK provided on RadarSearchRange and RadarSearchStrength is interesting and can be useful for modders when creating avionics for 3rd party AC :P

 

Edit: same as always, typos etc.

Edited August 3, 2010 by SFP1Ace

[+SkippyBing 8]

They can see bombers farther out, of course, but really as the radar outranges its longest-range weapons (AMRAAM and Sparrow), how much farther does it need to see them anyway?

 

As far as you can really, that allows you to manoeuvre your aircraft to the optimum position to engage while remaining safe yourself. Basically it increases your situational awareness.

 

As for ranges, and slightly off topic, the Blue Parrot set in the Buccaneer S.1 could detect shipping contacts at 240NM. It didn't bother displaying anything within ~100NM on the display at that setting mind otherwise getting an accurate range and bearing off the display would be tricky!