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Why people need to understand the difference between Designator and Detector


robgraham
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So I've tried to write this out about 5 times now in a way that doesn't end up that technical that we have about 5 pages of math and this is attempt number six, so I figured for the sixth attempt I'd try and just dumb it down a lot. It seems to come up a lot that there has to be a 'bug' or a 'fault when a laser tracker only detects energy at a certain range that is far less then the designator can target. Lets use our beloved Apache as an example it can start to detect functional laser energy with it's TADS at 9999m, despite the fact that laser designators might be able to go 15km or even 25km etc this however seems to get people upset with the arguments being made that the laser is able to fire 15km or 25km and therefore should be detectable at the same.

The simple answer is, No it should not.

The reason for this is Physics, and that's why this is the sixth attempt to well write this, but it's why the topic name says people need to understand the difference between 'Designator' and 'Detector' they are not the same thing.

Lets take this rather simple plot that I have here (its an example it's not meant to be 100% scientific accurate), for the purpose of this discussion this is the amount of Laser energy hitting a target from 5 (red), 10 (green), 15 (blue) km on a 'perfect' day with no changes in any atmospheric issues between the point of each laser designator 

image.png

What you will notice is that over distance the amount of energy at the 'spot' falls and it's not a linear fall in reality either, once this energy hits the target it gets bounced and scattered and when it gets bounced only a fraction of it does so, this energy then plays the same 'game' of loosing well Energy as it travels, and it's this energy that the 'Detector' has to look for, which should tell you something as well here.. The further the designator from the target, the less energy that reaches the detector! 

That is why that detector has to be sensitive as hell to be able to detect the small amounts of energy that can reach it, and because of that it has to a lot like a radar does filter out returns, it does this in a lot of ways, some are by cryogenically cooling the sensor so that it's getting the least amount of 'noise' from itself, but others by using software to calculate a noise "floor" and cutting off any returns that fall below that floor. Because of this the Laser DETECTOR is generally (ok I'd say 'always' but always is a bad term) going to be less capable then the designator in terms of range when it comes to detecting the laser SPOT (the valid amount of laser energy to guide onto)

How much so? Well lets put it this way, in all the public documentation I've found on the subject including but not limited to an awesome paper by the Army Research Lab specifically on SAL (Semi Active Laser) Guidance, none of them bother publishing any tables that go beyond 10,000 meters for both eye and non eye safe mil spec lasers, why? Because anything beyond that range tends to start falling below the signal to noise ratio limits for the detectors. This information is further backed up by the public information for various SAL munitions, almost all of them have a 6nm/30,000ft range limit on their seekers. Why? because if you do the math that's 10km.


And the thing is that 10km range or 9999Meter limit in the Apache or any of those guided munitions? that is literally for a 'perfect average' day, days aren't perfectly average, most days have haze and dust and all that and on those days typically your lucky if the detector gets enough energy to get a lock at Sea Level before it hits 5km.

But remember, Designator SHOOTS the energy.

Detector 'Spots' it.

And their ranges of 'function' can be very different.

----

Edit: If you want a paper that goes into this in a LOT of depth, including how the guidance etc works that is public do a search for ARL-TR-5654 - A terminal Guidance Model for Smart Projectiles Employing a SEmi-Active Laser Seeker.

It covers both the physics of the Designator, the Detector and even the impact of the Atmosphere etc all while also showing you how to do a computerised model on it.


Edited by robgraham
adding a further investigation source
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So how far away can an f18 be to spot the laser designator from an apache? Obviously if apache is closer to the target, more energy is reflected since the intensity increases as the square of the distance to target decreases. But laser energy arriving at f18 decreases with square of slant range. These two compensating effects might cancel out suggesting a maximum length for apache slant range to target plus f18 slant range to target. (Assuming apache and f18 have similar detectors). What is this theoretical length?
 

9999m?

 

So if apache is 3000 m to target then f18 munition has to acquire the reflected laser when it is 6999 m slant range away. I suppose the f18 could drop the munition blind from 30000 ft and hope for the best. But for f18 to detect the laser and show it in the cockpit, wouldnt it need to be closer than 6999 slant range if apache is 3000? Assuming a 45 degree slant, that means an altitude of about 5000 m. ?

 

this neglects details like obscuration at ground level by dust and by clouds at altitude. And if apache is 5000 m away, f18 has to be 5000 away which at 45 deg is ~3500 m altitude -  kind of low and at that altitude vulnerable to aaa and iglas. Might as well just go ccip or ccrp.

 

anybody with real world experience please tell us standard target ranges for jtac and f18 when doing this kind of buddy lasing

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Just to bring some additional context to the discussion, laser energy also needs to reflect at the correct angles for detectors to see the designation spot as well. If the laser designator is directly north of a target and an F-18 is coming from the south looking for that designation reflection, they might not see it. There are some other factors in play that affect this as well, such the shape, surface characteristics, and specific contours of the target, the angle it is being lased from, and how much of the laser beam is actually striking the target.

I believe what the OP's intent was is to bring awareness to some of the debates regarding how far lasers in DCS travel, and what a given laser should be capable of achieving in game with respect to designations, laser spot trackers, weapon guidance, etc. Some may desire a specific and universal real-world number for comparison, where everything works fine below and nothing works beyond it. But the point is that there is no universal number; because lasers are not a perfect targeting device.

Add to that the fact that no two lasers are exactly the same. A laser designator carried by an individual is not going to have the same power and range as one carried on an aircraft or mounted on a vehicle, just as a laser onboard a LITENING pod is different than one carried in the AH-64D's TADS. The real numbers and performance of these items are usually not available to the public, or the specific tactics and techniques to employ them under various circumstances. Players can still employ reasonably authentic scenarios within DCS, but there may be situations where a DCS laser designation slightly overperforms or underperforms compared to real-world equivalents; characteristics of which are often not available due to security reasons.

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2 hours ago, Raptor9 said:

just as a laser onboard a LITENING pod is different than one carried in the AH-64D's TADS

Another important distinction here, just to complicate things further... a LITENING pod am board a jet 10km above the target is shooting through considerably less atmosphere than one on a helicopters 10km laterally from a target at 100m altitude...  The average density of the air between surface and 10km is less than half the density of air at sea level.  Thicker air means more atmospheric scattering which means less energy reaches the target and less of the reflected energy makes it back.

 

it may well be realistic for a Hornet at 30km altitude and 30 km lateral range to pick up a laser fired by a Predator orbiting at a 5k radius and 10km altitude, just because there is so much less AIR in the way of the laser.

That doesn't mean that an Apache at 100m altitude would be able to pick up that same laser from 30km range, even with a perfectly clean LoS

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@Raptor9I apppreciate your reply. I understand that there are many details interfering with detection of the laser-reflectivity of the target, atmospheric conditions, intervening interference,etc. But I am trying to simplify the mechanics of JTAC-aggressor teams. Does the combined slant range of designator and detector have an upper limit? Isnt there a 'procedure' with recommended altitudes/distances ?

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From what I understand, the DCS laser beam does have a hard upper limit for simulation purposes, but I am not sure what that limit is currently. And the DCS laser doesn't simulate all the other minute factors that affect laser emissions in real life, like atmospherics. Simulating that degree of optical disturbances wouldn't just affect the laser beam, it would affect electro-optical sensors as well.

My comment wasn't necessarily directed at what you specifically typed (if that is what you were inferring), I was just commenting that the many threads that debate how far the DCS laser should go rarely take into account the litany of real-life physics that are far beyond the scope of a video game.

If you are asking for real-life range capabilities and limitations of real-world equipment, that gets into potentially sensitive topics and I won't go there, nor should anyone else. It's neither necessary for gaming nor relevant to DCS given the nature of how DCS simulates laser designations.

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9 minutes ago, Raptor9 said:

From what I understand, the DCS laser beam does have a hard upper limit for simulation purposes, but I am not sure what that limit is currently. And the DCS laser doesn't simulate all the other minute factors that affect laser emissions in real life, like atmospherics. Simulating that degree of optical disturbances wouldn't just affect the laser beam, it would affect electro-optical sensors as well.

My comment wasn't necessarily directed at what you specifically typed (if that is what you were inferring), I was just commenting that the many threads that debate how far the DCS laser should go rarely take into account the litany of real-life physics that are far beyond the scope of a video game.

If you are asking for real-life range capabilities and limitations of real-world equipment, that gets into potentially sensitive topics and I won't go there, nor should anyone else. It's neither necessary for gaming nor relevant to DCS given the nature of how DCS simulates laser designations.

Semi-related but we've been waiting a while now for the L of the RLWR system in the Apache, is there any reason they didn't just copy/paste the KA50's and call it day?

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6 minutes ago, placsea said:

Semi-related but we've been waiting a while now for the L of the RLWR system in the Apache, is there any reason they didn't just copy/paste the KA50's and call it day?

These systems are not the same.

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On 1/25/2023 at 7:02 AM, robgraham said:

So I've tried to write this out about 5 times now in a way that doesn't end up that technical that we have about 5 pages of math and this is attempt number six, so I figured for the sixth attempt I'd try and just dumb it down a lot. It seems to come up a lot that there has to be a 'bug' or a 'fault when a laser tracker only detects energy at a certain range that is far less then the designator can target. Lets use our beloved Apache as an example it can start to detect functional laser energy with it's TADS at 9999km, despite the fact that laser designators might be able to go 15km or even 25km etc this however seems to get people upset with the arguments being made that the laser is able to fire 15km or 25km and therefore should be detectable at the same.

The simple answer is, No it should not.

The reason for this is Physics, and that's why this is the sixth attempt to well write this, but it's why the topic name says people need to understand the difference between 'Designator' and 'Detector' they are not the same thing.

Lets take this rather simple plot that I have here (its an example it's not meant to be 100% scientific accurate), for the purpose of this discussion this is the amount of Laser energy hitting a target from 5 (red), 10 (green), 15 (blue) km on a 'perfect' day with no changes in any atmospheric issues between the point of each laser designator 

image.png

What you will notice is that over distance the amount of energy at the 'spot' falls and it's not a linear fall in reality either, once this energy hits the target it gets bounced and scattered and when it gets bounced only a fraction of it does so, this energy then plays the same 'game' of loosing well Energy as it travels, and it's this energy that the 'Detector' has to look for, which should tell you something as well here.. The further the designator from the target, the less energy that reaches the detector! 

That is why that detector has to be sensitive as hell to be able to detect the small amounts of energy that can reach it, and because of that it has to a lot like a radar does filter out returns, it does this in a lot of ways, some are by cryogenically cooling the sensor so that it's getting the least amount of 'noise' from itself, but others by using software to calculate a noise "floor" and cutting off any returns that fall below that floor. Because of this the Laser DETECTOR is generally (ok I'd say 'always' but always is a bad term) going to be less capable then the designator in terms of range when it comes to detecting the laser SPOT (the valid amount of laser energy to guide onto)

How much so? Well lets put it this way, in all the public documentation I've found on the subject including but not limited to an awesome paper by the Army Research Lab specifically on SAL (Semi Active Laser) Guidance, none of them bother publishing any tables that go beyond 10,000 meters for both eye and non eye safe mil spec lasers, why? Because anything beyond that range tends to start falling below the signal to noise ratio limits for the detectors. This information is further backed up by the public information for various SAL munitions, almost all of them have a 6nm/30,000ft range limit on their seekers. Why? because if you do the math that's 10km.


And the thing is that 10km range or 9999Meter limit in the Apache or any of those guided munitions? that is literally for a 'perfect average' day, days aren't perfectly average, most days have haze and dust and all that and on those days typically your lucky if the detector gets enough energy to get a lock at Sea Level before it hits 5km.

But remember, Designator SHOOTS the energy.

Detector 'Spots' it.

And their ranges of 'function' can be very different.

----

Edit: If you want a paper that goes into this in a LOT of depth, including how the guidance etc works that is public do a search for ARL-TR-5654 - A terminal Guidance Model for Smart Projectiles Employing a SEmi-Active Laser Seeker.

It covers both the physics of the Designator, the Detector and even the impact of the Atmosphere etc all while also showing you how to do a computerised model on it.

 

Thanks!

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To explain it a little more in depth for those interested with out still going too deep into the math and why the comments about 'height' etc are correct yes height matters for both the Designator and the Detector, lets use your common 'laser pointer' that most people can buy as an example, you may believe that the 'point' on it remains the same size and strength etc but it does not, shining the laser dot at 2 ft and then at 200ft will give you very different 'dot' sizes and the energy registered if you had a meter under each dot would be different. 

The reason for this is multifold, you have imperfections in the optics of the laser, you have dust in the atmosphere, you have water etc etc the later part is what is termed atmospheric diffusion/absorption and it causes 'scattering' of the beam. Now you have your laser and it fires out, hits the target.. At this point lets say we have a 1,000 Watt laser (this is all hypothetical.. we are just plucking values from thin air here ok) now that's 1,000w at the emitter, our target is 1km away (i'm keeping the math easy) or 1,000 meters. We are at Sea Level, now depending on the atmospheric conditions at sea level our laser might loose 1 watt of energy for every 100 meters it travels in that atmosphere... so when it hits the target it's now at 900 watts of energy.

At the same time that energy will no longer be the exact small 'point' either.. 95% of it will fall within a specific 'range' typically at a km that might be say 50cm or so but it's not 'pin point' if you follow. So we have 900 watts of energy and it's hitting the target and 95% of that is well of any real use to us so 855 Watts of energy. Now at the same time the Object itself is going to absorb some of that energy as well about 40% of it if you use the basic math for most objects, now it varies depending on the material, the colour etc etc but we are going to go with the standard 40% ratio that is in most of the math, so of that 855 watts of useable energy well 40% just got absorbed and made unusable so we lost 342watts of energy just there.. we now have 513 Watts of useable energy, but that energy isn't going to reflect evenly 'back' either.. The angle of the object it's hitting, the surface of the object, the material type that all impacts the way the energy now scatters from the object itself.. the amount of scatter can be anything it really depends on the object this is called diffusion.

Now at the same time as this we have the Detector.. for the first part here we will say the detector is 1km further away from the emitter and only 1 or 2 degree's off that out of the diffused scatter 50% of that 513 watts is 'bounced' at an angle back towards the deflector... now we have 256watts of energy returning towards the emitter.. but it has to go through all of that atmosphere AGAIN. 

So we lost 100 WATTS of energy just going 1km we are going 2km now.. the amount of energy we loose doesn't suddenly change.. (well ok it can but we are simplifying here a LOT ) so in our theory we have 100 watts lost for 1,000meters.. so 2,000meters we loose 200watts of energy.. we now have 56 watts of energy hitting the detector.

Now that same designator from a Hornet at 30,000ft might not loose that 100 Watts of energy on the way to the target, it might only loose 40 Watts of energy due to differences in atmosphere.. or maybe it looses 250 Watts because the laser catchs the edge of a cloud and gets diffused etc etc.

You can start to see why it matters in the real world..

In DCS not so much, DCS has magic lasers and sensors that don't get impacted by atmosphere (currently) and  Raptor and other's have done an amazing job of describing the reasons and the explanation for game terms as well as real life in the posts after me.

But DCS as much as this will 'upset' certain people is a Simulator GAME, it's an abstraction of reality, and limitations get put in place not only because of lack of information being public, but also because some times 'simplification' gives you the same results with FASTER CODE.

It might take me 200ms to simulate how much beam energy hits a target and gets to my pod using a full physics model.. 

Or it might take me 2ms simply by firing a set of raytracing rays and having it calculate if within x distance any of them intersect the target.... 

Code time matters some times.. and before some one goes 'MT will fix all that'... No, some times MT won't fix these types of calculations, that's just computer life.

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On 1/25/2023 at 7:02 AM, robgraham said:

it can start to detect functional laser energy with it's TADS at 9999km

Oh my... That's quite the range. I think you got the wrong unit there 😛

That aside, the issue isn't that the Apache can't detect above 10km. It might very well be able to do that with the equipment. The issue is that there is a software limit. Right now the laser doesn't behave right. It shows 9999m between 10km and 15km, like it should, but still gets the correct range on the TSD and when storing target points. Above 15km it just doesn't update anything, which is also wrong. It should just say 9999m if it doesn't get any energy back.

The current hard limit for laser range in DCS is a slant range of 15000m. Aka the laser is a single ray, cast from the designatior with length 15km. As far as I can tell, there is no real limit to detection of that spot.

Another thing to add would be that if I were to fire the laser at 12km, even if I can't pick it up, the laser should still hit something. If i then fire a laser guided missile in the general direction, it should be able to pick that up after traveling maybe 4km or so.


Edited by FalcoGer
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On 1/31/2023 at 7:05 AM, FalcoGer said:

Oh my... That's quite the range. I think you got the wrong unit there 😛

That aside, the issue isn't that the Apache can't detect above 10km. It might very well be able to do that with the equipment. The issue is that there is a software limit. Right now the laser doesn't behave right. It shows 9999m between 10km and 15km, like it should, but still gets the correct range on the TSD and when storing target points. Above 15km it just doesn't update anything, which is also wrong. It should just say 9999m if it doesn't get any energy back.

The current hard limit for laser range in DCS is a slant range of 15000m. Aka the laser is a single ray, cast from the designatior with length 15km. As far as I can tell, there is no real limit to detection of that spot.

Another thing to add would be that if I were to fire the laser at 12km, even if I can't pick it up, the laser should still hit something. If i then fire a laser guided missile in the general direction, it should be able to pick that up after traveling maybe 4km or so.

 

Yes, as far as we know there is no detection limit other than line of sight, although I assume each system/aircraft could model that if the coders chose, and some may indeed do that. The laser beam itself in DCS is 15km long, and terminates at the end of that line or on the first object it intersects with. If that point is in mid-air because there is no object/terrain that will still function as a laser designation, and detectors will still pick up the point in space as if there was a designated object there reflecting laser energy. As far as I know nothing else is modelled on a DCS-wide level, although the Apache appears to have a few things other modules don't such as backscatter modelling of some kind. 


Edited by Scaley
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