Gents,
There seems to be a bit of misunderstanding on both sides about this speculation.
First...What does the letters 'A W A C S' stands for:
Airborne
Warning
And
Control
System.
Second...Where does it say that an AWACS is restricted only to active sensor, ie radar? Nowhere.
Third...Can radar (microwave) be used to detect an infrared (IR) field? There are some highly theoretical work about this technique involving extremely high freqs because the microwave and infrared bands are pretty much next door to each other, but the concept is still far from being applicable, as in 'trickle' down to our level that for now the answer must be 'No'.
Am going to stray off a bit here: Radar detection is an active sensor with the 'R' stands for 'radio', as in using the microwave region. Technically speaking, there is nothing to say that we cannot use the other regions in the EM spectrum and we already have with the laser, as in 'infrared laser'...
Far-infrared laser - Wikipedia, the free encyclopedia
Far infrared laser (FIR laser, terahertz laser) is a laser with output wavelength in far infrared part of the electromagnetic spectrum, between 30-1000 µm (300 GHz - 10 THz).
Take note of the freq range: ghz - thz. We already have triple-digits freq radar systems, as in very high millimetric imaging radar whose target resolutions approaches that of B/W photographic quality.
Optics InfoBase - Terahertz radar cross section measurements
We perform angle- and frequency-resolved radar cross section (RCS) measurements on objects at terahertz frequencies.
But that is for another discussion.
The current technology with active sensor is that it is highly directional, as in 'beam forming' and we already about that here. When we say that the AWACS has 360 deg coverage, we do not mean at the same time. We mean that we can steer that beam -- more like cone or very thin fan -- to any point in a circle. Obviously, an electronic beam steering method will be superior -- as in speed -- to a mechanical one. But the essence of this diversion is still the same: That an active sensor system in the IR region that is capable of field deployment in a combat environment is still quite a ways off.
Back to topic...
Can an AWACS detect an IR emitting vehicle? Yes,
IF the AWACS is equipped with a dedicated IR sensor, after all, there is nothing to say that only radar can be airborne but not IR sensor. We already have airborne IR sensor as in 'heat seeking' missile.
Can an AWACS be equipped solely of passive IR sensor? Yes, but the problem with passive sensor is that there is no ranging information. The system can only tell us the direction of the IR emission. If the IR source is moving, we can perform some fanciful math based upon variable intensity due to distance changes to give us range information, but that leave us vulnerable to other IR sources that may be in the area whose intensity and physical proximity approaches our target's, contaminating our math. We know about this problem with the earlier generation Sidewinder missile being distracted by the sun. So an all passive AWACS is out of the discussion.
This leave us with an AWACS that contain both active and passive sensor exploiting different areas of the EM spectrum. The advantage with a passive IR sensor system is that it can be designed to be either a wide field of view (FoV) or as narrow as we want. An AWACS certainly have room for both types. The US Navy's E2C AWACS fleet has both active radar and passive IR sensors. What happens is that the wide FoV IR sensor detect an IR contrast, meaning there is an IR emission that is considerably higher than the background's IR emission. This information is then transmit to the active sensor system, as in a cue or a clue-in, so that the active sensor system can (re)direct its more precise beam to that IR source. With a mechanical beam control system, this will require some time for the radar beam to approach the IR source. For an AESA system, the redirection will be quite instant.
To the Indian members here, sorry, but the Brahmos is not 'stealth' or not as 'stealthy' as you would like to believe. What constitute being 'stealthy' involve different areas or modes of detection: radar, IR, acoustic, and visual. The last item include physicality such as dimensions and shape of the vehicle and whether or not the vehicle produces smoke or contrails in flight. The missile can have low radar observability but if its IR emission is high enough to produce that contrast then it violated the advice of being 'balanced stealth'.
The question is: How soon into flight will that contrast be available for detection by any passive sensor in the area? That depends on acceleration and the Brahmos is supersonic, no?
Can I reach Mach 1 with an acceleration of 100km/hr or 1000km/hr? Yes to both. Can I reach Mach 1 with an acceleration of merely 1km/hr? Absolutely. The higher the acceleration the sooner I will reach Mach 1 but also the sooner I will produce that IR contrast.
Contrary to popular belief, during supersonic flight, it is not skin friction IR emission that produces the greater IR contrast but compressed air being heated up during -- what else -- being compressed. Below supersonic is when skin friction IR emission matter. At supersonic speed, skin friction IR is a contributor to total IR emission, but not necessarily the dominant.
The Science Pundit: Air friction myths
As an object moves through the air, it displaces the air in its path by pushing it forward and aside. The air moves away from the object as a series of compression waves (similar to the waves that a boat creates as it moves through the water).
What happens is that the air gets pushed forward and aside faster than it can naturally escape. As long as the object is moving slower than sound, the compression waves outrace it and take most of their energy with them. But at supersonic speeds, the air keeps getting compressed and compressed and compressed as the object pushes it forward faster than the air can get away.
Basically, the supersonic object creates its own oven by compressing the air in front of it.
The lower the flight altitude the higher this compressed air IR emission will be due to the denser atmosphere. This leave the Brahmos -- in my opinion -- not merely vulnerable but highly vulnerable to an AWACS that contains and integrate active and passive sensors, aka 'data fusion' and we are not talking about an IR operator shouting his finding down the corridor to the radar operator or even if they sit next to each other. We are talking about the IR sensor computer directly linked to the radar computer complete with video integration of both the IR and radar backgrounds.
