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TWS mode not being able to detect targets that fly in a formation


Invictus_ds

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Hello

We, as a little community enjoying F14 in DCS, would like to ask you, developers, about TWS mode not being able to detect targets that fly in a formation:

First video: There are four Tu-22 on a line abreast formation with a 4nm lateral separation.

Second video - same four Tu-22, but this time only 0.7nm lateral separation. How come, that on TWS mode the radar does not show four target tracks at a distance? On the first video, all targets had their own tracks at only 88nm distance, while in RWS mode, radar shows all four tracks separately even at max detection range On the second video, with the radar in TWS mode, targets where all detected only at 15nm range! RWS had them at max range again...

Is it supposed to be like that? Its weird, that F14 fighter, that was designed to stop Soviet bomber horde from long range in TWS mode, cannot even separate target tracks if enemy planes fly formation. I doubt, that NATO had an agreement with the Soviet Union as to only attack US carriers in a spread formation with 10+nm separation...

First flight.acmi Second flight.acmi

First flight.trk

Second flight.trk


Edited by Invictus_ds
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46 minutes ago, Lt_Jaeger said:

There is a thing like radar resolution cell and the lack of computing power in these early radars.

"The track while scan mode uses the same FM ranging as RWS with the same reduction in range compared to pulse doppler search and the DDD display is also the same. The main difference that the computer establishes track files and tracks up to 24 targets concurrently of which 18 can be shown on the TID at any given time" - F-14 manual.

Is seems like a bug for me.

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Also beware the bandits might be inside the radar shadow of other bandits. Best practice in multiship intercepts is to probably split the section and approach the contacts from different vectors and or altitudes. Datalink between the fighters may also help? Not sure about the latter, never had the chance to test it myself. 

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36 minutes ago, xarann said:

Same targets, same ranges, same lateral separation, same hardware. RWS mode - we see all four bandits, and only two of them in TWS

TWS merging radar returns is normal and how the actual radar functioned. It didn't have the same resolution, particularly due to the 2 second scan cycle. 

More the case that DCS Hornets and Vipers don't have TWS shortfalls accurately implemented which is the problem; after all why have a SCAN RAID function if the radar sees it perfectly anyway?

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On 6/12/2022 at 7:30 PM, Panny said:

TWS merging radar returns is normal and how the actual radar functioned. It didn't have the same resolution, particularly due to the 2 second scan cycle.

Can you explain what is the difference between RWS and TWS modes in terms of radar resolution?

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Hold my beer. Worlds worst analogy coming in.

If you're old enough to remember the first digital cameras then its a similar idea. The analog part of the system, for a camera the lens, for the radar the transmitter / receiver / logic gates is a very highly developed very good resolution system.

The digital part is the camera sensor / computer processing the TWS tracks into trackfiles, which turns the very sharp analog image into a much blockier lower resolution image.

Similarly to cameras the digital version is better, after its been developed and refined, but at least in the short term its actually worse in some respects than the analog system its replacing.

In RWS the AWG-9 is just painting analog returns onto an analog display but because these are very high end very expensive systems you can actually make out the distinction between 2 very close together returns, thats not the computer doing it, its just your eye discerning a good display.

TWS is different, here the raw returns aren't shown to the user but trackfiles are, and due to computing limitations of the time (remember the CPU in the F-14 would be beaten by your average calculator in the 1990s) the return is divided into what are called cells.

To continue the analogy think of this as representing an image with only a limited number of pixels, say 200x200. 

In the F-14 those cells are much wider than later jets, from memory (and dont quote me on this) something close to 5 degrees and 1nm plus or minus. As the targets get closer and closer you can start to break those apart in terms of azimuth particularly, where you'll start to see 2 tracks, but fundamentally that's the problem.

Digital processing with a generation 0 CPU.

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On 6/14/2022 at 8:10 PM, AH_Solid_Snake said:

Hold my beer. Worlds worst analogy coming in.

<eaten by mise>

Digital processing with a generation 0 CPU.

I'm pretty sure that all the information we see on the TID must first be processed by the WCS (i.e. converted from a raw analog to a digit), so if the WCS sees four bandits in RWS and draws them on the TID, then the same should be in TWS.

And we come back to the question: what is the difference (if there is one at all) between the RWS and TWS modes in terms of radar resolution.

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The difference is, in RWS you're working with radar resolution. In TWS, you're working with cells. If you have two hits within one cell, they get lumped into a single track, because the system can't tell between two hits coming from two different planes, and two hits coming from a single aircraft. It assumes the latter. Processing done in TWS is far more extensive than in RWS.

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@xarann- im trying to figure out exactly what the question you're asking is, when people give you pointers to why it doesn't work the way you expect you don't seem to ask for clarification, you reject the answer and then repeat that TWS should be just as good as RWS? What are you basing that assumption on?

To try again to boil it down, the radar in RWS mode can give pretty precise information on a given return, for example the antenna angle off the nose was 2 deg up, 4 deg left, with a time for return of 3s, that gives us a target on the scope at 20nm - all of that is precise and has almost no digital computer processing going on.

The problem is the computer running this very first generation TWS implementation can't handle running the entire flow for up to 24 tracks in real time with that degree of precision, so a cheat is used. We introduce cells and we divide up our radar picture into blocks, looking kind of like a chessboard. Now we can make the math a little bit simpler (and therefore easier for our slow CPU to perform at the speed desired) but its kind of like playing the old battleships game.

In pass 1 i saw a return in cell A1 going to my right and towards me, I assume next time the scan zone passes over this track it will have moved to cell B2 so i set a trackfile expecting to find a return in B2 next time we arrive there, if my guess was right I update my file and recompute my guess, now its coming head on so i expect to see it in B3 on the next pass, and so on and so on.

By necessity these cells are large in comparison to the raw returns, so getting a single return in a cell can mean theres literally 1 target, or it can mean that there are really 2, we just cant break them out yet. As we close range eventually we will, and the single trackfile will be thrown away and 2 new trackfiles will be generated in adjacent cells.

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2 hours ago, WelshZeCorgi said:

One situation that confuses me is when on the DDD, there are two distinct contact with space between them, but in the fishbowl, in TWS, the track files still get confused and mixed up occasionally at distance. 

The DDD is still and always will be the PRIMARY instrument. The TID is an Assistant to aid spatial awareness. The RIO needs to work the DDD to get the AWG-9 to perform. Which allows them to manual adjust the TID well, which the Pilot then uses up front. 
 

Don’t think of the AWG-9 like the Strike Eagle or Two seat Super Hornet. The back seat is there to do the work the pinball machine can’t.

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13 minutes ago, WelshZeCorgi said:

My question is how any program can take 2 distinct contacts fed to it from the DDD and still think it's one contact. 

Quite possibly the track building algorithm is unable to distinguish them correctly as both contacts fall into the track prediction model (basically an oval superimposed on top of the last radar hit, and the last position of the track thereafter), so the contacts are merged into a single track.

There's also the matter of DCS natively lacking a radar cell representation, which at that distance might have been showing you  a merged contact in RWS as well.


Edited by GGTharos
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11 hours ago, GGTharos said:

Quite possibly the track building algorithm is unable to distinguish them correctly as both contacts fall into the track prediction model (basically an oval superimposed on top of the last radar hit, and the last position of the track thereafter), so the contacts are merged into a single track.

There's also the matter of DCS natively lacking a radar cell representation, which at that distance might have been showing you  a merged contact in RWS as well.

 

The DDD image is the same for RWS and TWS modes, so the raw radar data is the same for both modes (the initial data for calculations are the same).

Four separate contacts in RWS must correspond to four separate tracks in TWS mode. Why can the target representation algorithm for RWS mode distinguish all bandits clearly, but cannot do the same in TWS?

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50 minutes ago, xarann said:

The DDD image is the same for RWS and TWS modes, so the raw radar data is the same for both modes (the initial data for calculations are the same).

Four separate contacts in RWS must correspond to four separate tracks in TWS mode. Why can the target representation algorithm for RWS mode distinguish all bandits clearly, but cannot do the same in TWS?

As other users has mentioned probably because alot more info has to be processes to build a track file. (limited cells) 

 

By this logic TWS should have same range as RWS but the latter has an advantage. 


Edited by Comstedt86
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1 hour ago, xarann said:

The DDD image is the same for RWS and TWS modes, so the raw radar data is the same for both modes (the initial data for calculations are the same).

Four separate contacts in RWS must correspond to four separate tracks in TWS mode. Why can the target representation algorithm for RWS mode distinguish all bandits clearly, but cannot do the same in TWS?

Fun thing to try - RWS is also somewhat susceptible to it. If you set a fighter formation that's extremely tight, the RWS will also show it as one contact on the TID. RWS does FM ranging, and has a resolution, but considering its purpose, RWS will just throw out whatever radar return; it's up to the RIO to correlate it.

It's speculation on the decisions of the Hughes engineers, but considering TWS needs the view a radar contact once every two seconds to build a track, there's a significantly higher degree or error that's involved, and limited processing to work it. As stated earlier, DCS Hornet and Viper give the impression to people that TWS has an incredible resolution, and somehow instantaneously builds tracks without doing any radar correlation. IRL however, they would use modes such as SCAN RAID to try and pick targets out due to TWS' susceptibility of merging contacts.

1 hour ago, Comstedt86 said:

 

By this logic TWS should have same range as RWS but the latter has an advantage. 

 

null

TWS does have the same range as RWS. The core difference isn't in the AWG-9, but the WCS building tracks off what the radar is providing.

image.png

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1 hour ago, Comstedt86 said:

As other users has mentioned probably because alot more info has to be processes to build a track file. (limited cells) 

By this logic TWS should have same range as RWS but the latter has an advantage.

I do not know where they got this information from, but processing data from the radar for display on the TID  is nothing like the operation of a digital camera.

Everything displayed on TID has already been digitized, there is no analog information there! And why is it that a computer(our WCS) having the same source data (from DDD) can separate them as four targets in RWS, but in TWS mode "sees" only two of them? TID image should be the same for both modes

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1 hour ago, Panny said:

Fun thing to try - RWS is also somewhat susceptible to it. If you set a fighter formation that's extremely tight, the RWS will also show it as one contact on the TID. RWS does FM ranging, and has a resolution, but considering its purpose, RWS will just throw out whatever radar return; it's up to the RIO to correlate it.

It's speculation on the decisions of the Hughes engineers, but considering TWS needs the view a radar contact once every two seconds to build a track, there's a significantly higher degree or error that's involved, and limited processing to work it. As stated earlier, DCS Hornet and Viper give the impression to people that TWS has an incredible resolution, and somehow instantaneously builds tracks without doing any radar correlation. IRL however, they would use modes such as SCAN RAID to try and pick targets out due to TWS' susceptibility of merging contacts.

null

TWS does have the same range as RWS. The core difference isn't in the AWG-9, but the WCS building tracks off what the radar is providing.

image.png

Thanks, was under the impression TWS had slightly lower range. 

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5 hours ago, xarann said:

The DDD image is the same for RWS and TWS modes, so the raw radar data is the same for both modes (the initial data for calculations are the same).

Four separate contacts in RWS must correspond to four separate tracks in TWS mode. Why can the target representation algorithm for RWS mode distinguish all bandits clearly, but cannot do the same in TWS?

There is no algorithm for RWS.   TWS is all algorithm, the radar hit is an input to it.   And the reason is because the oval (not cells) that's put around a hit has to be of a certain size to guarantee track maintenance.

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You're confusing incoming data with algorithms.   RWS is fairly raw, it produces a hit with a specific position which can be sent to TWS.

TWS receives the positions and figured out how to build a track from that.  If two hits fall inside the same track oval one may be rejected or they can be merged for TWS, whatever the TWS algorithm is programmed to do in that case.


Edited by GGTharos

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