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In the modern air-naval-land warfare, in addition to fighter aircraft, IRST technology is employed in maritime air defence systems, as well as in battle tank Active Protection Systems (APS). With the development of data fusion in modern combat systems, significant improvements in effectiveness can be achieved with the combination, association and correlation of data from multiple sensors and sources, such as the radar and IRST system (range – angular precision).
Stealth aircraft, apart from their Radar Cross Section (RCS) reduction, employ techniques reducing their IR signature, as well. Such techniques are the omission of an afterburner (as in the case of the F-117 and B-2), the use of high bypass ratio turbofan engines (where the bypass stream is used to cool the exhaust gases), and the placement of the exhaust duct on the top, in an effort to hide the hot gases from below (as in the case of B-2). Some aircraft use their fuel as coolant, transferring waste heat to it, e.g., the F-35. Despite all these efforts, it is simply impossible to make such a heat source, as a fast flying aircraft, disappear in the IR band. Therefore, IRST systems appear to be a viable anti-stealth approach.
InfraRed Search & Track (IRST) systems are non-imaging devices exploiting initially LWIR and later LWIR or MWIR, for air-to-air detection and targeting purposes.
MWIR:
Mid Wave IR thermal cameras are capable of achieving the longest range detection for thermal infrared surveillance cameras and are often cooled via cyro-cooler, allowing them to offer extreme range with high contrast and little noise. MWIR Infrared is a subset of the infrared band of the electromagnetic spectrum, covering the wavelengths ranging from 3µm to 5µm (3000nm to 5000nm).
LWIR
Long-wave or LWIR infrared is a subset of the infrared band of the electromagnetic spectrum, covering the wavelengths ranging from 8 µm to 14µm (8,000 to 14,000nm). Uncooled LWIR thermal imaging can be more affordable than cooled MWIR thermal imaging, as the sensors require less complex components and less ongoing maintenance. Large aperture can allow more thermal energy to reach the sensor, which results in a cleaner and sharper image.
Most FLIR/IRST systems are MWIR and LWIR capable.
Some words of AIM-9
Initial versions (up to AIM-9J) used a PbS detector in the Short-Wave IR band (1.9-2.6 μm), while following versions (from AIM-9L to AIM-9P) were equipped with an InSb one (4μm, MWIR), permitting “all aspect” engagements (attack from all directions, not only from the rear quarter). With each new version, there were improvements regarding mainly missile range and guidance system, where more advanced detector technology allowed longer detection ranges, while was also efficiently rejecting Infrared Counter Measures (IRCM), such as flares. The latest version is the AIM-9X Block II, employing a MWIR Mid Wave IR focal plane array seeker.
IRST Field of View
A modern IRST sensor would exhibit an array of 640×512 detectors, while the next generation will have an array size of 1024×1024. Each frame is divided to pixels, depending on the array size of the sensor. The frames an IRST can see depend on the field of view. The three fields of view are:
1. Wide Field Of View (WFOV): 30 (deg) × 24 (deg)
2. Medium Field Of View (MFOV): 16 (deg) × 12.8 (deg)
3. Narrow Field Of View (NFOV): 8 (deg) × 6.4 (deg)
(Approximate degrees, they may vary from system to system)
The wider the field of view is, the easier to look at the direction of the target but also more sky radiation (noise) will be in the frame, reducing the contrast. On the other hand, a narrow field of view would provide a good contrast, due to less sky radiation entering the frame, allowing the detection of a target from far away, provided that the sensor is looking at the target. A more dense array (with more pixels) means that less sky radiation will enter each pixel, including the pixel of detection.
IR systems are more sensitive than Radar to adverse weather conditions.
Considering an aircraft chasing enemy stealth aircraft (F-35) and flying on its tail. Approximate values of Field of views (in simulations) in different weather conditions are given below. IRST detection range values are in km, at high altitude. The enemy aircraft engine is on dry thrust (no afterburner) and the IRST system is looking at the target aircraft from behind.
From above simulated results, it is clear that, in good weather conditions, a target (e.g., an F-35) can be detected at quite long distances, or even longer (100 km+) in drought conditions.
Realistic distances (such as 80+ km) comparable to above results in scenario of F-35 detection have been noted in:
Ingmar A. Andersson, Leif Haglund, SAAB IRST: the system and flight trials, Proc. SPIE 4820, Infrared Technology and Applications XXVIII, (2003).
It is noted that the above table takes into account only the engine hot parts, seen from behind, and not aerodynamic friction.
As the weather conditions are getting worse, the performance of the IRST deteriorates. At heavy rainfall or snow, IRST detection range becomes quite poor. However, in most cases, IRST detection range is better than the expected detection range of a stealth jet by a typical tactical aircraft radar.
The field of view significantly affects performance. As FOV gets wider, the contrast between target and background is reduced and the performance is poor. On the other hand, for narrow FOV, the performance is considerably better. However, it is more difficult to use such a narrow mode for detection.
Content referenced from; Research Gate.
So which is the maximum range a stealth fighter aircraft would be detected by an IRST sensor?
AND
Which are the most important parameters affecting this range?
The above questions will depend on:
1. Modelling of the target aircraft engine, based on characteristics of a typical turbofan engine. (e.g F135, the powerplant of the F-35)
2. Analysis of the weather conditions and atmosphere transmittance.
3. Analysis of the IRST sensor, i.e., detector, optics, etc., using characteristics and parameters pertaining to FLIR system.
4. Estimation of maximum detection distance based on the radiant intensity difference between target and background.
Furthermore;
1. Would this also change the dynamics of air combat between PAF and IAF in cold/snowy weather conditions of Kashmir and the scorching hot deserts in Sindh ?
2. Would performance of IR (WVR) missiles as well as FLIR systems (for detection or tracking) get affected as such in different weather conditions ?
3. Would BVR combat become dominant between PAF and IAF since IR has limitations in different weather conditions ?
4. Pakistan is investing heavily in Radar systems, as the FLIR system capability is retained on aircraft such as F-16's.
5. TOP GUN schools of both PAF and IAF would have certainly considered the factor of air to air combat in different weather conditions for employing IR missiles and systems. Whats your take on:
a. Air to air employment of WVR/IR missiles in extreme climates/geography (cold and warm)
b. FLIR systems in adverse systems in PAF and IAF combat scenario.
Stealth aircraft, apart from their Radar Cross Section (RCS) reduction, employ techniques reducing their IR signature, as well. Such techniques are the omission of an afterburner (as in the case of the F-117 and B-2), the use of high bypass ratio turbofan engines (where the bypass stream is used to cool the exhaust gases), and the placement of the exhaust duct on the top, in an effort to hide the hot gases from below (as in the case of B-2). Some aircraft use their fuel as coolant, transferring waste heat to it, e.g., the F-35. Despite all these efforts, it is simply impossible to make such a heat source, as a fast flying aircraft, disappear in the IR band. Therefore, IRST systems appear to be a viable anti-stealth approach.
InfraRed Search & Track (IRST) systems are non-imaging devices exploiting initially LWIR and later LWIR or MWIR, for air-to-air detection and targeting purposes.
MWIR:
Mid Wave IR thermal cameras are capable of achieving the longest range detection for thermal infrared surveillance cameras and are often cooled via cyro-cooler, allowing them to offer extreme range with high contrast and little noise. MWIR Infrared is a subset of the infrared band of the electromagnetic spectrum, covering the wavelengths ranging from 3µm to 5µm (3000nm to 5000nm).
LWIR
Long-wave or LWIR infrared is a subset of the infrared band of the electromagnetic spectrum, covering the wavelengths ranging from 8 µm to 14µm (8,000 to 14,000nm). Uncooled LWIR thermal imaging can be more affordable than cooled MWIR thermal imaging, as the sensors require less complex components and less ongoing maintenance. Large aperture can allow more thermal energy to reach the sensor, which results in a cleaner and sharper image.
Most FLIR/IRST systems are MWIR and LWIR capable.
Some words of AIM-9
Initial versions (up to AIM-9J) used a PbS detector in the Short-Wave IR band (1.9-2.6 μm), while following versions (from AIM-9L to AIM-9P) were equipped with an InSb one (4μm, MWIR), permitting “all aspect” engagements (attack from all directions, not only from the rear quarter). With each new version, there were improvements regarding mainly missile range and guidance system, where more advanced detector technology allowed longer detection ranges, while was also efficiently rejecting Infrared Counter Measures (IRCM), such as flares. The latest version is the AIM-9X Block II, employing a MWIR Mid Wave IR focal plane array seeker.
IRST Field of View
A modern IRST sensor would exhibit an array of 640×512 detectors, while the next generation will have an array size of 1024×1024. Each frame is divided to pixels, depending on the array size of the sensor. The frames an IRST can see depend on the field of view. The three fields of view are:
1. Wide Field Of View (WFOV): 30 (deg) × 24 (deg)
2. Medium Field Of View (MFOV): 16 (deg) × 12.8 (deg)
3. Narrow Field Of View (NFOV): 8 (deg) × 6.4 (deg)
(Approximate degrees, they may vary from system to system)
The wider the field of view is, the easier to look at the direction of the target but also more sky radiation (noise) will be in the frame, reducing the contrast. On the other hand, a narrow field of view would provide a good contrast, due to less sky radiation entering the frame, allowing the detection of a target from far away, provided that the sensor is looking at the target. A more dense array (with more pixels) means that less sky radiation will enter each pixel, including the pixel of detection.
IR systems are more sensitive than Radar to adverse weather conditions.
Considering an aircraft chasing enemy stealth aircraft (F-35) and flying on its tail. Approximate values of Field of views (in simulations) in different weather conditions are given below. IRST detection range values are in km, at high altitude. The enemy aircraft engine is on dry thrust (no afterburner) and the IRST system is looking at the target aircraft from behind.
From above simulated results, it is clear that, in good weather conditions, a target (e.g., an F-35) can be detected at quite long distances, or even longer (100 km+) in drought conditions.
Realistic distances (such as 80+ km) comparable to above results in scenario of F-35 detection have been noted in:
Ingmar A. Andersson, Leif Haglund, SAAB IRST: the system and flight trials, Proc. SPIE 4820, Infrared Technology and Applications XXVIII, (2003).
It is noted that the above table takes into account only the engine hot parts, seen from behind, and not aerodynamic friction.
As the weather conditions are getting worse, the performance of the IRST deteriorates. At heavy rainfall or snow, IRST detection range becomes quite poor. However, in most cases, IRST detection range is better than the expected detection range of a stealth jet by a typical tactical aircraft radar.
The field of view significantly affects performance. As FOV gets wider, the contrast between target and background is reduced and the performance is poor. On the other hand, for narrow FOV, the performance is considerably better. However, it is more difficult to use such a narrow mode for detection.
Content referenced from; Research Gate.
So which is the maximum range a stealth fighter aircraft would be detected by an IRST sensor?
AND
Which are the most important parameters affecting this range?
The above questions will depend on:
1. Modelling of the target aircraft engine, based on characteristics of a typical turbofan engine. (e.g F135, the powerplant of the F-35)
2. Analysis of the weather conditions and atmosphere transmittance.
3. Analysis of the IRST sensor, i.e., detector, optics, etc., using characteristics and parameters pertaining to FLIR system.
4. Estimation of maximum detection distance based on the radiant intensity difference between target and background.
Furthermore;
1. Would this also change the dynamics of air combat between PAF and IAF in cold/snowy weather conditions of Kashmir and the scorching hot deserts in Sindh ?
2. Would performance of IR (WVR) missiles as well as FLIR systems (for detection or tracking) get affected as such in different weather conditions ?
3. Would BVR combat become dominant between PAF and IAF since IR has limitations in different weather conditions ?
4. Pakistan is investing heavily in Radar systems, as the FLIR system capability is retained on aircraft such as F-16's.
5. TOP GUN schools of both PAF and IAF would have certainly considered the factor of air to air combat in different weather conditions for employing IR missiles and systems. Whats your take on:
a. Air to air employment of WVR/IR missiles in extreme climates/geography (cold and warm)
b. FLIR systems in adverse systems in PAF and IAF combat scenario.
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