Question about Triangulation with infrared sensors

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armedupdate

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Unread post23 Jun 2016, 01:19

I have a question about finding range of enemy aircraft via triangulation with an infrared sensors. I heard the friendly airplanes have to be a bit far away from each other for reliable ranging. Also are their patterns such as flying in a zig zag pattern and changing speed, to avoid being locked on by this technique and to defeat the enemy midcourse updates to the missile.
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Unread post23 Jun 2016, 06:39

Triangulation with infrared sensors is totally possible and actually very accurate as IR (and other optical) systems have very fine angular resolution giving very accurate direction to target. Reliability of ranging is dependent on many factors, but generally aircraft involved in triangulation would be better off being widely separated while having very fast datalinks with very low latency and other delays to calculate accurate target position and range.

Changing direction, speed or zig zagging would not affect IR sensors at all as they don't rely on doppler or pulse modulation information for detecting targets like radars do. Only way of defeating IR sensors is staying out of their sight (staying out of their range or reducing emitted thermal energy) or getting some physical object between you and sensor (clouds, mountains).
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Unread post23 Jun 2016, 13:56

hornetfinn wrote:Triangulation with infrared sensors is totally possible and actually very accurate as IR (and other optical) systems have very fine angular resolution giving very accurate direction to target. Reliability of ranging is dependent on many factors, but generally aircraft involved in triangulation would be better off being widely separated while having very fast datalinks with very low latency and other delays to calculate accurate target position and range.

Changing direction, speed or zig zagging would not affect IR sensors at all as they don't rely on doppler or pulse modulation information for detecting targets like radars do. Only way of defeating IR sensors is staying out of their sight (staying out of their range or reducing emitted thermal energy) or getting some physical object between you and sensor (clouds, mountains).

And aren't we being told that a formation of F-35s will fly 10 or more miles apart? A 1-mil resolution would allow two planes 10 nm apart to triangulate a heat source at effectively unlimited distance.
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Unread post23 Jun 2016, 14:31

hornetfinn wrote:.

Changing direction, speed or zig zagging would not affect IR sensors at all as they don't rely on doppler or pulse modulation information for detecting targets like radars do.).

zig zagging wouldn't affect triangulation but will affect and neutralize single ship passive kinematics ranging
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Unread post23 Jun 2016, 14:34

RAdm. Mike Manazir quotes a 25 -mile combat spread for F-35s.
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Unread post23 Jun 2016, 14:50

sprstdlyscottsmn wrote:And aren't we being told that a formation of F-35s will fly 10 or more miles apart? A 1-mil resolution would allow two planes 10 nm apart to triangulate a heat source at effectively unlimited distance.

This made me wonder how the F-35's flying in that formation synchronizes their clocks, since together with the sensor data you have to send when exactly you took that measurement for a perfect triangulation (the speed of light alone will already cause a variable delay depending on the distance between the aircraft, about 0.05ms at 10nm for example).

I then read up on using GPS clocks and with that you can get to about 10ns accuracy (1ms is 1000000ns).

I also read about small atomic clocks, they are very small indeed and probably have the accuracy. The only thing I then wonder about is: how do they perform the initial sync between the ships in the formation? Does a base have a 'time sync device' to which all F-35 can sync their clocks at the start of a mission? And if needed can they still perform a (less) precise sync by GPS when F-35's from different bases meet up in the air?
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Unread post23 Jun 2016, 17:41

Two GPS receivers being only 25NM apart, each seeing the same 5+ satellites, would have virtually the same error, so the relative difference in the timing will be near or as good as zero.
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Unread post23 Jun 2016, 20:27

Don't the two friendly aircraft have to form right angles perpendicular to the enemy to perform Triangulation? What if the enemy attacks from the flanks of the formation? Also do you need to do it altitude wise?
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Unread post23 Jun 2016, 22:46

Think of it this way. Both F-35s know exactly where the other one is in relation to each other in three dimensional space (time stamped GPS data passing through MADL). Each one has an azimuth and elevation (A&E) to a contact through DAS or EOTS. Now think of that A&E information as a straight line extending from the aircraft. Each aircraft is sharing it's contact data (A&E) with the other so now each F-35 "sees" two lines going into space and these line intersect on one point in space only and can calculate the GPS location of that target. As time passes and the A&E data changes for each F-35 and the intersection point moves they have a full firing solution on a target using nothing more than EODAS or EOTS tracks. This all happens automatically and in real time for every track that shows up on DAS and EOTS. If the track is in the forward hemisphere than the APG-81 will probably send a tight beam to that point and verify the data. This has been the plan all along with the F-35 and it is why MADL and Sensor Fusion was so important. So when you hear that two-ship sensor fusion works fine and they are working on the four-ship sensor fusion you can start to get a feel for why it is so complex.

No, I don't have any "proof" that this is how it works, but I figured out that this is what happens over five years ago. This is why the F-35 is a game changer.
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Unread post27 Jun 2016, 10:56

I agree with Spurts. I'd like to add that F-35 sensor fusion system is very likely not using only IR systems to do the job, but using all available sensors and inputs to create as accurate picture as possible. If 2 F-35s see the target using only EOTS, 1 sees it using Barracuda and IFF system and one sees is using EO DAS, then all of those systems are involved in creating as accurate picture as possible. Not only would everyone in the flight know almost instantly where the target is through triangulating using all those sensors, but they would also know much more like type and whole lot of other data.

Overall F-35 is the only fighter aircraft that has all the required tools for high-accuracy triangulation. These are high-resolution imaging infra-red systems (EOTS and EO DAS), very high speed and low latency datalink (MADL) and sensor fusion to automatically combine the information together. EF Typhoon has tools to do triangulation with lower accuracy, lower information gathering abilities and at lower ranges (lower resolution and shorter range sensor). F-15s with Talon HATE pods or SH with IRST21 system might have some similar capabilities, although I doubt they are anywhere as extensive as in F-35.
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Unread post27 Jun 2016, 14:39

sometime i wonder why EOTS doesn't have a LWIR channel along with MWIR? LWIR deal better with low temperature targets so iam not sure why they are not integrated in EOTS? Advanced EOTS even have a SWIR channel but LWIR still not integrated, and it not like USAF not interested in LWIR or doesn't have adequate technology level, since AAS-42 and IRST21 both use LWIR
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Unread post27 Jun 2016, 14:40

Because with the F-35 these are all capabilities designed into the aircraft from the beginning.
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Unread post27 Jun 2016, 15:07

sprstdlyscottsmn wrote:Because with the F-35 these are all capabilities designed into the aircraft from the beginning.

what do you mean?
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Unread post28 Jun 2016, 00:41

eloise wrote:
sprstdlyscottsmn wrote:Because with the F-35 these are all capabilities designed into the aircraft from the beginning.

what do you mean?

Apologies, that is in response to the last bit of hornetfinn's post.
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Unread post28 Jun 2016, 13:57

eloise wrote:sometime i wonder why EOTS doesn't have a LWIR channel along with MWIR? LWIR deal better with low temperature targets so iam not sure why they are not integrated in EOTS? Advanced EOTS even have a SWIR channel but LWIR still not integrated, and it not like USAF not interested in LWIR or doesn't have adequate technology level, since AAS-42 and IRST21 both use LWIR


LWIR sensor can detect low temperature targets better than MWIR one, but in most cases high-performance MWIR sensor outperforms LWIR sensors. LWIR sensors are usually cheaper at same performance, but MWIR are able to reach higher performance. They have the advantage of higher resolution, higher sensitivity, higher temperature contrast and have wider temperature range. So MWIR systems create crisper and better images with less noise. LWIR sensor would not give much benefit for aircraft sensor. LWIR is used for example in anti-ballistic missile interceptors where background is very cool and homogenous (deep space) and targets can be very cool (no air friction to heat the ballistic missile warhead for example). At lower altitudes and against earth background they don't work as well as cooled MWIR sensors.

LWIR is easier and significantly cheaper to make (both detector and optics) and reasonable performance can be had without cooled sensor system. I would bet this is why AAS-42 and IRST21 are LWIR systems. LWIR is pretty good for searching targets, but it would not be as good for target recognition and identification due to reasons mentioned earlier.
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