IRST abilities

[moon_light]

i just read this article here theboresight.blogspot.co.uk/2009/07/airborne-infrared-and-supersonic.html?m=1 , they mentioned some really strange feature for IRST compared to what i have known such as measure range without LFR or measure velocity of target by Doppler (red/blue) shift , is the IRST really capable of doing such thing ?

The IRST might also use its own stored 'Atmospheric Propagation Model' to effectively “make an educated guess” as to target(s) relative range, aspect and velocity – without the radar or laser rangefinder. In effect the sensors own performance is characterized to construct a sensitivity model against known objects at known distances and velocities. Then during wartime when IRST sees something - it compares its own “known” internal Atmospheric Propagation Model - and the weapons system then extrapolates target range and bearing.

John C. Mather, Senior Astrophysicist at the Goddard Space Flight Center, Mars Society, University of Maryland 31-July, 2009; during his remarks on Doppler (red/blue) shift detection resolution-granularity in discussing astrophysics of celestial objects: “…we are able to see the velocity of a star down to one (1) meter per second.”


Advanced Flanker IRST Doppler-shift sensitivity will not require the granularity of astrophysics, because an F-22 Raptor traveling at Mach 1.1 will be moving at approximately 374 meters per second. By including air combat closure rates - this figure is even higher (!)


This would seem to fall well within, the definition of military useful sensitivity?


So in effect Advanced Flanker variants could affect engagement (with IR seeker R-77 class missile) of a supersonic radio-spectrum airfoil (an F-22) using - all available sensors - in five (5) ways:


1.)True-Positive (Doppler): IRST uses infrared Doppler-shift w/APM to determine target range.


2.) True-Positive (Laser): IRST uses infrared and verifies range to target with laser range-finder.


3.) True-Positive (Radar): IRST uses infrared and verifies range to target with radar.


4.) True-Positive (Cycle): IRST uses infrared and verifies range to target by cycling thru steps 1-2-3-repeat.


And finally...


5.) Conceptually one can act on a - 'False-Positive' - even if stealth is 100% effective in the radio spectrum:


a) IRST picks something up.
b) Point your radar at it.
c) No (or strange) radar return? = stealth.
d) We don't have stealth.
e) Select R-77 IR weapon - 'Fox!’


This discussion is in a way - academic. The Russians have already identified two main areas to exploit supersonic Raptor.


They revolve around, and loop back into these two issues:


• F-22 Primary weapon.
• F-22 Thermal signature.
The infinite logic of this - is clear. If Raptor attempts to improve her kinematic-situation by using high altitudes and high speeds – she will increase her thermal exposure. Any attempt to mitigate thermal propagation issues – by lower speeds or altitudes - directly impacts the power (reduces the range) of Raptors primary weapon.

According to Tom Clancy (Fighter Wing: A Guided Tour of an Air Force Combat Wing - Clancy Tom; Penguin Group, 1995), the F-22 Raptor is an 'F-15 Eagle’ weapons platform, in a stealthy supercruising airframe. The only problem with Clancy's description is that the F-15 Eagle was simply no match for the Tomcats combination of radar (+ IRST) and AIM-54 Phoenix missile. No match. Tomcat could also use AIM-9 and AIM-7 (AIM-120?) at longer ranges than Eagle.

Remember that IRST integration into the weapon system may produce an aircraft that is highly resistant to the "Beaming" / "Beam-turn" / "Doppler turn" maneuver used by an opponent to break radar locks - because the target now presents increased engine-heat aspect(s) to the sensor.

it also mention something very strange about rcs

Target RCS (Radar Cross Section) [below] is determined by: 1) the power transmitted in the direction of the target. 2) The amount of power that impacts the target and is reflected back in the direction of the radar. 3) The amount of reflected power that is intercepted by the radar antenna. 4) The length of time in which the radar is pointed at the target.
The issue here is an IRST (IR sensor) can be "slaved" to the radar, to follow whatever the radar is tracking, or the radar can be slaved to the IRST to track whatever the IR sensor(s) "see." So in effect: 'Time on Target' (Pay close attention to number “1” and "4" of the graphic above).

This would be consistent with publicly available information stating that Stealth prefers hostile “scanning” radar(s) over hostile “tracking” radar(s).

Remember Stealth is effectively a 'radio spectrum airfoil' and its intent is to passively reduce the power of (an opponents) "2" and "3". Stealth has no capability to control "1" and "4". It could produce some type of radio/radar jamming-deception transmission(s), but this then potentially reveals its position. Not an easy problem to resolve for the Stealth fighter - that requires own/friendly radio energy transmission(s) to employ its primary weapon at range. For the Stealth fighter problems are compounded because without own/friendly radio-transmission-targeting support, Stealth aircrews could be forced to fly into the maw of modern, hostile, IRST detection envelopes before F-22 can fire its weapons.

 

[Bonza]

For what it's worth, a lot of that sounds highly suspect to me. Understand that I do not have practical experience with IRST systems, but am simply reading critically. I mean they reference Tom Clancy as a source, for one thing, which for me puts their credibility at a point just above zero. They then go on to say the F-15 is "no match" for the F-14 - which is a simplistic analysis based seemingly on a "platform for platform" basis - that is to say, the author is simply looking at the stated capabilities of one aircraft and comparing it directly to another aircraft, and coming to the conclusion that because one aircraft had a different radar and a missile with a longer range (in optimal conditions), it must be the better one. This is typical of discussions that focus on warfare as if it is a boxing match, with the platforms engaging in a vacuum - it does not reflect the reality of how warfare is fought and how the battlespace is managed.

If I were you, I'd take it and anything else the author has to say with a massive grain of salt. In addition he's talking about IRST capabilities that, from what I understand, are theoretically possible but highly impractical - the example I was given several years back by someone with far more knowledge than myself was that most IRST systems are the equivalent of looking at the sky through a straw; sure, you could pick up a target with one, but using one to actively search for the target without first knowing the location of that target in some other way would be almost futile. So IRST won't simply "pick something up" the way he suggests.

Other people on the forum who know more may chip in but in short it sounds like he's talking utter BS to me.

 

[StobieWan]

It's one of those genius ideas that revolves around the target platform making no attempt to frustrate your attempts to track and kill it.


If you're trolling around the skies in a 3/4 G platform, relying on an IRST to detect a target before they see you and hoping they don't simply start manoeuvring aggressively, I suggest you're asking for a bit much luck.


IRST's have been around for decades and their range to detect, much less identify targets is rather less than the NEZ for an AIM120. Mainly I'd expect you to realise the bad guys were in the area right around the time an AIM120 went active just about six feet from your canopy.

As has been said, IRST's don't have a great field of view.

The negative test doesn't work either - if you're looking at a heat signature in the IRST, then you've likely no range to the target - you need to get that via some other means - laser or radar. Given that, how could you know what size radar return to expect? I suspect you'll be swallowing an AIM120 again here.

 

[moon_light]

i know that the article sound highly suspect but may be something that it mentioned was true , practical , i mean IRST like PIRATE on typhoon , AAS-42 on f-14D , tiger eye on F-15K , DAS on F-35 are all dont have Laser finder range so may be the method of determine range like mentioned in the article was possible ?
iam not sure about the ability of determine velocity though :unknown not very sure about doppler effect in infrared wavelength

 

[Todjaeger]

i know that the article sound highly suspect but may be something that it mentioned was true , practical , i mean IRST like PIRATE on typhoon , AAS-42 on f-14D , tiger eye on F-15K , DAS on F-35 are all dont have Laser finder range so may be the method of determine range like mentioned in the article was possible ?
iam not sure about the ability of determine velocity though :unknown not very sure about doppler effect in infrared wavelength

Having taken a quick look at the blog, it appears the author is assuming what/how an IR astronomical observatory functions is relevant to an IRST, or what the significant of having the observatory at high altitudes is.

Also the author of the blog does not seem to understand how Doppler shift is detected and used to determine the velocity of a celestial object.

In short, the blog is a bunch of techno-babble comparing dissimilar systems and capabilities and assuming that they are similar and compatible.

 

[StobieWan]

I think some of the writing demonstrates a pretty strange understanding of red shift effects.

"John C. Mather, Senior Astrophysicist at the Goddard Space Flight Center, Mars Society, University of Maryland 31-July, 2009; during his remarks on Doppler (red/blue) shift detection resolution-granularity in discussing astrophysics of celestial objects: “…we are able to see the velocity of a star down to one (1) meter per second.”


Advanced Flanker IRST Doppler-shift sensitivity will not require the granularity of astrophysics, because an F-22 Raptor traveling at Mach 1.1 will be moving at approximately 374 meters per second. By including air combat closure rates - this figure is even higher (!) "



Basically, that's taking a statement that a star's velocity can be measured to within one meter person and claiming that's the star's velocity. It's not - a star is usually travelling in one direction or another at speeds measured in kilometers per second.

In short, assumption one, that ranging an F22 will be easier than a star using red shift is totally incorrect. Neither do red shift effects show up well at short distances (under several million miles usually)

It's a bit like saying you can use a police radar gun to measure tree ring growth.