IRST ability

[moon_light]

i just read this article theboresight.blogspot.co.uk/2009/07/airborne-infrared-and-supersonic.html?m=1 , they mentioned some really strange feature for IRST 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.