Air to Ground Ranging (AGR)

[imacken]

The practical use of AGR? Accurate CCIP (or just CCIP in general as Santi said)

 

Sorry, I mean the practical use of displaying it on the DDI,

[imacken]

 

A only shows in a dive because the radar dish needs to be pointing down to see the ground. Obviously it can gimbal a certain amount, but it helps if the nose is pointed in the right direction.

Not sure about that as pressing SCS forward brings up the A in level flight with the relevant data on the DDI. The slant angle seems to be about 30 degrees in level flight as at a height of 15,000ft, the AGR slant range is 30,000ft. So, if my trigonometry is correct, that gives a slant angle of 30 degrees.

 

The practical use is accurate ranging and therefore more accurate CCIP and AUTO. Whether or not that difference is modeled correctly in sim is still up for debate. The greatest difference / effect should be when either BARO or RAD ALT ranging can't be relied on.

Sorry, as I said above, what I meant was what is the practical use of displaying the data on the DDI.

 

[AvroLanc]

Not sure about that as pressing SCS forward brings up the A in level flight with the relevant data on the DDI. The slant angle seems to be about 30 degrees in level flight as at a height of 15,000ft, the AGR slant range is 30,000ft. So, if my trigonometry is correct, that gives a slant angle of 30 degrees.

 

 

Sorry, as I said above, what I meant was what is the practical use of displaying the data on the DDI.

 

Yeah OK, I did notice a few issues with the 'A' display which I though were a bit odd. I need to test more. I would still expect AGR to be most accurate at steeper slant/grazing angles.

 

Oh, the DDI. Well I guess it still has to display something when switching from 'map'. The alternative would be a blank screen or a raw video 'strobe' return. Obviously you wouldn't be referring to the slant range data 'live' in flight. If the DDI recorders are set to record the DDI's the data might be useful for post-flight debriefing / technique analysis.

[imacken]

Oh, the DDI. Well I guess it still has to display something when switching from 'map'. The alternative would be a blank screen or a raw video 'strobe' return. Obviously you wouldn't be referring to the slant range data 'live' in flight. If the DDI recorders are set to record the DDI's the data might be useful for post-flight debriefing / technique analysis.

 

Well, it doesn't really have to display anything, does it? If it is on, i.e. with an A below the altitude box, then it doesn't display anything on the DDI. It's only when SCS is pressed forward that we see anything.

[Fri13]

 

The A only shows up when you are in a dive. I wonder if this has something to do with AUTO as you are likely to be in level flight for that.

 

I still am wondering what practical use this all is!

 

 

Our hornet radar doesn't have a narrow beam capability as a AESA radar would offer. So the radar is not capable for accurate ranging because of the flashlight effect.

 

 

As you can see, the radar beam stays same, but it will "lit up" a larger area of the terrain when it is pointed in smaller angle. In 90 degree angle you get most accurate ranging, but with 1-15 degree you are trying to range a very long range between the closest and furthest part of the beam edges to you. So you can only take the whole range value (that is changing) and try to calculate a median from it and assume that is correct one.

 

So AGR mode to be automatic only at dives higher than 7 degree is to avoid trying to range a ridiculous long range. This same thing is related to the terrain itself, as if you are diving downhill, your relative angle is very shallow. If you are diving uphill then your relative angle is much higher.

 

Here is example:

 

 

Your radar beam is few degrees, but the similar problem exist. Shallower your dive on target, then much longer the ranging area is and computer needs to try to estimate what is the center or the expected target by strongest echo.

Using just your altitude (radar for AGL, barometric for ASL) and angle, speed etc, you are not going to be very accurate at all if your target is not on same altitude as your aircraft is relative to ground below you, and barometric doesn't even know what ground altitude is unless your firing computer receives that information from other means, like TAMMAC database, using GPS to know where you are and where you are pointing at.

 

This is as well reason why AGR is not accurate ranging method as you need to come in very deep angles at the target to get relative accurate bombing solution. And why the ARBS system that A-4 and Harrier had was superior as it could calculate very accurate target position and range by measuring angle changes relative to all other flight parameters as long it could keep contrast lock on the target and it was given enough time and changes in angle rate to calculate the solution. But as it was day-time TV only mode, with contrast lock requirement, it was not great against low contrast targets (majority of targets) and it was not all-weather or night time capable system that the radar is.

 

The other best methods is to use laser, like a laser range finder in Su-25A or Su-25T (as well used angle rate method) with Shkval, and so on. When you can range the distance with laser, you still have a similar flashlight effect, but much more minor if there is strong reflection. This similar thing is simulated in Su-25A where laser range finder starts jumping as you go shallower dive or level flight as the laser beam is so wide that it gets reflections from various ranges. This same challenge is with the ground vehicles laser ranging systems where you can get echoes and then system will tell you that ranging is not accurate, and you can get various range values on each measurement.

 

The AGR mode is just one main methods to do the slant ranging at ground target but it requires you have proper approach parameters for it. Why it automatically being disabled when diving under 7 degree is wise thing as you are likely very very inaccurate then, and only when you go for very deep dives you start to get more accurate range data. And if you anyways are using targeting pod for target search and designation, you have laser to give slant range to target with few meter accuracy if you have good weather, no counter measurements, target is not covered with laser suppressive materials etc, but you can always try to range something near by.

 

And eventually if you are dropping a 250-500 kg iron bombs, you don't need to be super accurate. Even a ~40 kg HE artillery shell will be extremely dangerous for modern MBT from 30-50 meters, and effective up to 100-150 meters if lucky. So much more destructive bomb is neglecting the aiming errors fairly well, but it is then about terrain and position where you drop the bomb by its angle. Like it is no use so much if target is behind a huge rock or behind a small ditch and bomb explodes opposite side of cover.

This is reason why Mavericks were developed, to be more accurate but very short range "bomb". 3-5 km lock ranges for optimal cases with other than K, and this is why the laser maverick is the more used as you can get little longer launch ranges and you have less problems with the vertical differences (like buildings etc) that optical guided ones doesn't like, or other non-high contrasty targets (concealed vehicles, buildings etc).

 

The AGR feature is just nice to have there. It is not excellent, neither is A-G radar etc. The best way still is that you get laser dot from close distance on the target, you fly as much you can from behind the laser so the reflection is strongest possible and you get the weapon in optimal proximity to guide toward that dot.

 

[Fri13]

 

Well, it doesn't really have to display anything, does it? If it is on, i.e. with an A below the altitude box, then it doesn't display anything on the DDI. It's only when SCS is pressed forward that we see anything.

 

You do want to know what ranging method you have going, so you know how to adapt your flying and weapons release to it.

There are very odd things going on the Hornet designs, I have some doubts for some functions as they don't make sense, but when it is said that they are different from the USN variant then it likely is so, no matter how odd.

ED has changed many things in Hornet in later patches that has required players adapt to new ways to do things, and it has caused confusion. And it is evidence for nothing else than ED receives lots of conflicting information and are uncertain for many things and they need to and try answer questions "how this is done in real thing".

 

 

[imacken]

 

You do want to know what ranging method you have going, so you know how to adapt your flying and weapons release to it.

 

Yes, but we know what ranging method is being used by the letter below the altitude box. The info on the DDI doesn't add anything to that.

 

(I'll try and absorb the info in your other post later!)

 

[maxTRX]

Yes, but we know what ranging method is being used by the letter below the altitude box. The info on the DDI doesn't add anything to that.

 

(I'll try and absorb the info in your other post later!)

 

I have to verify in the sim but out of top of my head... If you had anything else on that DDI like FLIR, it would not switch to AGR screen. When you have ground radar on it, it simply switches modes. Yea, I would probably put something more useful there, then again, this 'useless' screen only shows when you put TDC priority on HUD and you are focused on HUD.

Also, having 'AGR' displayed when targeting via HUD is probably useful in case you have to reject AGR for whatever reason. You want to keep your eyes on HUD and have only seconds to make that decision.

[hein22]

No idea how it gets range/alt data for CCIP in hornet TBH. Might be Baro, might be Radalt, might be DTED (even though ED say our hornet shouldnt have that), might be AGR

 

Wait what? Our hornet DOES have DTED. When did ED say that? Link?

[imacken]

Also, having 'AGR' displayed when targeting via HUD is probably useful in case you have to reject AGR for whatever reason. You want to keep your eyes on HUD and have only seconds to make that decision.

 

Sorry to keep repeating myself, but we already know if AGR is being used because of the A under the altitude box. We don't need to SCS forward to see that.

[imacken]

 

 

Our hornet radar doesn't have a narrow beam capability as a AESA radar would offer. So the radar is not capable for accurate ranging because of the flashlight effect.

 

[ATTACH=JSON]{"data-align":"none","data-size":"medium","data-attachmentid":7134037}[/ATTACH]

 

As you can see, the radar beam stays same, but it will "lit up" a larger area of the terrain when it is pointed in smaller angle. In 90 degree angle you get most accurate ranging, but with 1-15 degree you are trying to range a very long range between the closest and furthest part of the beam edges to you. So you can only take the whole range value (that is changing) and try to calculate a median from it and assume that is correct one.

 

So AGR mode to be automatic only at dives higher than 7 degree is to avoid trying to range a ridiculous long range. This same thing is related to the terrain itself, as if you are diving downhill, your relative angle is very shallow. If you are diving uphill then your relative angle is much higher.

 

Here is example:

 

[ATTACH=JSON]{"data-align":"none","data-size":"full","data-attachmentid":7134036}[/ATTACH]

 

Your radar beam is few degrees, but the similar problem exist. Shallower your dive on target, then much longer the ranging area is and computer needs to try to estimate what is the center or the expected target by strongest echo.

Using just your altitude (radar for AGL, barometric for ASL) and angle, speed etc, you are not going to be very accurate at all if your target is not on same altitude as your aircraft is relative to ground below you, and barometric doesn't even know what ground altitude is unless your firing computer receives that information from other means, like TAMMAC database, using GPS to know where you are and where you are pointing at.

 

This is as well reason why AGR is not accurate ranging method as you need to come in very deep angles at the target to get relative accurate bombing solution. And why the ARBS system that A-4 and Harrier had was superior as it could calculate very accurate target position and range by measuring angle changes relative to all other flight parameters as long it could keep contrast lock on the target and it was given enough time and changes in angle rate to calculate the solution. But as it was day-time TV only mode, with contrast lock requirement, it was not great against low contrast targets (majority of targets) and it was not all-weather or night time capable system that the radar is.

 

The other best methods is to use laser, like a laser range finder in Su-25A or Su-25T (as well used angle rate method) with Shkval, and so on. When you can range the distance with laser, you still have a similar flashlight effect, but much more minor if there is strong reflection. This similar thing is simulated in Su-25A where laser range finder starts jumping as you go shallower dive or level flight as the laser beam is so wide that it gets reflections from various ranges. This same challenge is with the ground vehicles laser ranging systems where you can get echoes and then system will tell you that ranging is not accurate, and you can get various range values on each measurement.

 

The AGR mode is just one main methods to do the slant ranging at ground target but it requires you have proper approach parameters for it. Why it automatically being disabled when diving under 7 degree is wise thing as you are likely very very inaccurate then, and only when you go for very deep dives you start to get more accurate range data. And if you anyways are using targeting pod for target search and designation, you have laser to give slant range to target with few meter accuracy if you have good weather, no counter measurements, target is not covered with laser suppressive materials etc, but you can always try to range something near by.

 

And eventually if you are dropping a 250-500 kg iron bombs, you don't need to be super accurate. Even a ~40 kg HE artillery shell will be extremely dangerous for modern MBT from 30-50 meters, and effective up to 100-150 meters if lucky. So much more destructive bomb is neglecting the aiming errors fairly well, but it is then about terrain and position where you drop the bomb by its angle. Like it is no use so much if target is behind a huge rock or behind a small ditch and bomb explodes opposite side of cover.

This is reason why Mavericks were developed, to be more accurate but very short range "bomb". 3-5 km lock ranges for optimal cases with other than K, and this is why the laser maverick is the more used as you can get little longer launch ranges and you have less problems with the vertical differences (like buildings etc) that optical guided ones doesn't like, or other non-high contrasty targets (concealed vehicles, buildings etc).

 

The AGR feature is just nice to have there. It is not excellent, neither is A-G radar etc. The best way still is that you get laser dot from close distance on the target, you fly as much you can from behind the laser so the reflection is strongest possible and you get the weapon in optimal proximity to guide toward that dot.

 

 

Thanks for the detailed response. Food for thought. I was under the impression that the AGR slant range was to the centre of the beam. If that is the case, then it shouldn't, in theory, matter what the dive angle is. However, that doesn't square with the slant range being at a 30 degree angle in level flight.

[maxTRX]

 

Sorry to keep repeating myself, but we already know if AGR is being used because of the A under the altitude box. We don't need to SCS forward to see that.

 

'A/R/B' is showing you what MC is doing in the background based on limitations of radar, altimeter, etc. When you enable AGR by bumping the SCS up (in some situations you might be on the HUD already) you simply have the confirmation you are OK with using AGR. When you decide to reject it you will have the confirmation when the AGR disappears. The need for rejecting AGR might come in handy when Auto acquisition is used, if I remember correctly from the other sim.

Currently, when you have A/G gun selected w/o any designation you can also cancel AGR by pressing 'undesignate' (pinky) switch. Also, in the other sim you could force the gun reticle to disregard AGR and use the Max range of 5k ft. by pressing 'cage/uncage'

It's been a while so certain things might be getting a little hazy...

[Swift.]

 

Wait what? Our hornet DOES have DTED. When did ED say that? Link?

 

This is where the confusion comes from, when I made a wishlist item for TAMMAC, ED said its not planned. TAMMAC for the uninitiated was the upgrade to hornet that brought in features like DTED and CIB.

 

To add to the confusion, our hornet has TAWS, which is reliant on DTED. Also the TPOD gets magic coords and range, even though we 'dont have DTED'.

 

So yes, I'm being heavily sarcastic, just to highlight the foolishness in not giving us TAMMAC.

[Frederf]

The thing is in real life how do you know what the center of the beam is? The antenna sends out energy, it's reflected, and it comes back later. The antenna gets a signal which is simply a value changing in time. It kinda looks like

[ATTACH=JSON]{"data-align":"none","data-size":"full","data-tempid":"temp_261768_1605031216406_386","title":"ascope.jpg"}[/ATTACH]​

 

Of course there are methods to try to compensate for the different ranges. It's a good assumption that early times are due to a short round trip distance caused by the lower limb of the beam reflecting off closer terrain and getting back sooner. Conversely later times (longer range) is from the upper limb of the beam going farther beyond the center point and reflecting.

 

A simplistic approach to estimate the range to the center of beam is to take the average of the ranges. Of course the beam path length difference isn't the same 1 degree below center and 1 degree above. But if radar knows INS dive angle and assumes the ground is level this effect can be mathematically compensated for. Of course radar beam isn't like a triangle with hard edges. It softly falls away off center so the "edge" is up for debate. The radar would have to guess what angle off axis a particular part of the return signal represents and the difference in graze angle (and distance) means that return strength is reduced more for shallow, long trip than it is for steeper, short trip. You can take all of this info, assumptions about atmospheric attenuation, range return loss, reflection coefficient of terrain, effect of angle on reflection and calculate what range the center of radar lobe is. But if you get really low angle this process just isn't practical any more.

 

Tank commanders (e.g. M1A1) have a similar problem except in range with lasing. They have really small grazing angles and lots of foreground and background objects to their target. In their case they can select "first return" "last return" or I think an average. If there are a bunch of trees between you and a target tank then you pick last return. If the tank target is in open ground and there's a background hill you want first return.

[Fri13]

 

Thanks for the detailed response. Food for thought. I was under the impression that the AGR slant range was to the centre of the beam. If that is the case, then it shouldn't, in theory, matter what the dive angle is. However, that doesn't square with the slant range being at a 30 degree angle in level flight.

 

If you take the radar beam width and height (IIRC it is about 2.5 x 3 degree or something) then you can calculate the minimum beam resolution from it. It doesn't get smaller than that.

Example with 3 degree beam angle, at 3500 range you get 183 wide beam (you can use either meters or feets or whatever, ratio stays same). And that if you tilt off from 90 degree angle, you start to get the extra error for the ranging smaller that angle is (shallower dive).

 

The AGR is as well pointed to some given angle depending what is wanted, like for the backup HUD reticle (top right corner) it is that position, or if you enable CCIP then it should be used dynamically adjusted to give you the slant range for the pipper.

But it does cause trouble as explained shallower you go, variable terrain elements (different doppler returns and all). It just brings that challenge that what radar needs to believe that is the proper wanted target position. CLoser you get, more accurate you become too as beam width gets smaller.

 

 

[hein22]

 

This is where the confusion comes from, when I made a wishlist item for TAMMAC, ED said its not planned. TAMMAC for the uninitiated was the upgrade to hornet that brought in features like DTED and CIB.

 

To add to the confusion, our hornet has TAWS, which is reliant on DTED. Also the TPOD gets magic coords and range, even though we 'dont have DTED'.

 

So yes, I'm being heavily sarcastic, just to highlight the foolishness in not giving us TAMMAC.

 

I agree. Without DTED our hornet will be nothing but a fast A-10A with radar. Not to mention that many current systems are using DTED like CCIP, TGP, etc. I just wish ED says something about this... someday.

[Fri13]

So yes, I'm being heavily sarcastic, just to highlight the foolishness in not giving us TAMMAC.

 

Wonder why so important feature is withold?

[Harker]

 

Wait what? Our hornet DOES have DTED. When did ED say that? Link?

 

Here you go https://forums.eagle.ru/forum/englis...ption?t=260332

 

I don't understand why they're going this route. Even if they only keep the CHRT display (although we already have both ALT maps for DTED and SAT maps for CIB in the game), they could at least implement the rest of the TAMMAC functions.

[Swift.]

 

Here you go https://forums.eagle.ru/forum/englis...ption?t=260332

 

I don't understand why they're going this route. Even if they only keep the CHRT display (although we already have both ALT maps for DTED and SAT maps for CIB in the game), they could at least implement the rest of the TAMMAC functions.

 

Or even just fix the way the Mode display is laid out. I mean the CIB and DTED options could even just be blank. It would be better than whatever it is we have now, imo

[imacken]

 

If you take the radar beam width and height (IIRC it is about 2.5 x 3 degree or something) then you can calculate the minimum beam resolution from it. It doesn't get smaller than that.

Example with 3 degree beam angle, at 3500 range you get 183 wide beam (you can use either meters or feets or whatever, ratio stays same). And that if you tilt off from 90 degree angle, you start to get the extra error for the ranging smaller that angle is (shallower dive).

 

The AGR is as well pointed to some given angle depending what is wanted, like for the backup HUD reticle (top right corner) it is that position, or if you enable CCIP then it should be used dynamically adjusted to give you the slant range for the pipper.

But it does cause trouble as explained shallower you go, variable terrain elements (different doppler returns and all). It just brings that challenge that what radar needs to believe that is the proper wanted target position. CLoser you get, more accurate you become too as beam width gets smaller.

 

 

Could you just explain why the slant range appears to be 30 degrees in level flight? Thanks.

[Fri13]

 

Could you just explain why the slant range appears to be 30 degrees in level flight? Thanks.

 

Now I didn't understand?

30 degree slant range?

 

Are you meaning the CCIP pipper designator position that can be under HUD so it can be calculate?

[imacken]

 

Now I didn't understand?

30 degree slant range?

 

Are you meaning the CCIP pipper designator position that can be under HUD so it can be calculate?

 

See my post #27 above. In level flight at 15,000 feet, the AGR slant range shows as 30,000 feet. By my calcs, that means the beam is at 30 degrees. In the context of the discussions, I don’t understand that.

[Fri13]

 

See my post #27 above. In level flight at 15,000 feet, the AGR slant range shows as 30,000 feet. By my calcs, that means the beam is at 30 degrees. In the context of the discussions, I don’t understand that.

 

How much does an average pilot see down from the HUD if raising a seat? Could it be 30 degree down, so if in AUTO mode you could get a designation pipper to bottom of your HUD as in Harrier, that your AGR is measuring slat range to that angle that you can visually designate?

 

 

[imacken]

 

How much does an average pilot see down from the HUD if raising a seat? Could it be 30 degree down, so if in AUTO mode you could get a designation pipper to bottom of your HUD as in Harrier, that your AGR is measuring slat range to that angle that you can visually designate?

 

 

Sorry, I don’t understand what you are meaning. I’m saying that a CCIP pipper beam is at 30 degrees in level flight, and I can’t see how that fits in with what was discussed above.

[Fri13]

 

Sorry, I don’t understand what you are meaning. I’m saying that a CCIP pipper beam is at 30 degrees in level flight, and I can’t see how that fits in with what was discussed above.

 

If your beam would be pointing straight forward in level flight, you would be always ranging the air unless flying toward mountain (and crash at it).

 

So.... Wouldn't it be logical to have radar pointing downward when you are flying at level so that radar would have a possibility to range you a possible impact point for the weapon you have to be dropped?