Can IR camera see through clouds?

[Emu]

Though the IRST vs. stealth fighter is a difficult story. The big advantage is that it is passive. You don't know that the aircraft is there. For the stealth fighter now to see the aircraft, it has to use it's radar, giving away the stealth benefit. The stealth figther also has to continusly emit to allow for target search. The IRST can run for the whole time without emitting anything.

That's the problem with the latest phase-interferometric RWRs. Using your radar isn't necessarily a good idea since it provides targeting information for your opponent before it provides targeting information for you.

[NeilWillis]

IR is a heat signature, and if the clouds are dense and cold, they cannot be seen through. If they are not particularly dense, then heat will penetrate, and therefore be picked up on the detector.

 

It's all down to physics, and the sensitivity of the device, along with favourable atmospheric conditions.

[Invader ZIM]

Regarding radar, for me the question would be, do you actually have a RWR that is capable of the processing power to even pick up an LPI AESA radar?

 

One of the so called Low Probability of Intercept (LPI) modes of operation possible with AESA radar works like this. Instead of forming one beam at full power and searching for targets that way, the radar forms hundreds of very weak but very precise beams. The aggregate power output is the same, but at any one point in time on any one bearing the signal is basically at the same level as the background hiss. The frequency is also randomized but logged by the LPI radar. To a RWR there is nothing but the same background hiss as the rest of the sky. But the LPI radar knows to look for a specific hiss level spike on a specific frequency for a specific bearing at a specific time. It integrates these over time. If nearly every single time slice shows hiss level spike at the identified frequency for that bearing and time slice, there is a return. If it shows random spikes and valleys there's nothing there.

 

In order to do this the radar must have the ability to generate hundreds of different beams at varying frequencies all at once. This requires an AESA. Only the transmitting AESA radar has the when, at what frequency and down what bearing to look for the a particular hiss behavior. The RWR which does not have the specific log of when at what frequency the very weak signals should be arriving over time only sees background static.

 

Date: 7/1/2000; Publication: Journal of Electronic Defense; Author: Sweetman, Bill

 

CIP software controls the APG-77 according to emission-control principles. The radar's signals are managed in intensity, duration and space to maintain the pilot's situational awareness while minimizing the chance that its signals will be intercepted. More distant targets get less radar attention; as they get closer to the F-22, they will be identified and prioritized; and when they are close enough to be engaged or avoided, they are continuously tracked.

 

Sensor fusion and emission control are closely linked. The more the datalinks and ALR-94 can be used to build and update the tactical picture, the less the system needs to use the radar. The IFDL provides another layer of protection against tracking, because any one F-22 in a flight can provide radar data to the others.

 

A target which is using radar to search for the F-22 or other friendly aircraft can be detected, tracked and identified by the ALR-94 long before its radar can see anything, at ranges of 250 nm or more. As the range closes, but still above 100 nm, the APG-77 can be cued by the ALR-94 to search for other aircraft in the hostile flight. The system uses techniques such as cued tracking: since the track file, updated by the ALR-94, can tell the radar where to look, it can detect and track the target with a very narrow beam, measuring as little as 2[degrees] by 2[degrees] in azimuth and elevation. One engineer calls it "a laser beam, not a searchlight. We want to use our resources on the high-value targets. We don't track targets that are too far away to be a threat."

 

The system also automatically increases revisit rates according to the threat posed by the targets. Another technique is "closed-loop tracking," in which the radar constantly adjusts the power and number of pulses to retain a lock on its target while using the smallest possible amount of energy.

 

High-priority emitters -- such as fighter aircraft at close range -- can be tracked in real time by the ALR-94. In this mode, called narrowband interleaved search and track (NBILST), the radar is used only to provide precise range and velocity data to set up a missile attack. If a hostile aircraft is injudicious in its use of radar, the ALR-94 may provide nearly all the information necessary to launch an AIM-120 AMRAAM air-to-air missile (AAM) and guide it to impact, making it virtually an anti-radiation AAM.

 

The ALR-94 drives the F-22's defensive displays. The system determines the bearing, range and type of the threat, and then computes the distance at which the enemy radar can detect the F-22.

 

 

 

Personally, I'm skeptical, because even U.S. aircraft going against F-22's have had problems knowing they were being painted by the APG-77. And I would think that F-15C, F-16's and F-18E RWR's aren't really slouches when it comes to sensitivity and picking up emitters, neither is the Typhoons RWR for that matter, and all claimed they had no chance at BVR against the APG-77 system.

Edited June 2, 2014 by Invader ZIM

[Emu]

Regarding radar, for me the question would be, do you actually have a RWR that is capable of the processing power to even pick up an LPI AESA radar?

That's the question isn't it.

 

Theory, which is always easier than implementation, suggests that you could integrate the energy across all wavelengths and find the direction where there's more energy, then use phase interferometry to work out which waves are coming from a moving aircraft by sequential position calculations.

 

In reality though, there's probably not only different frequencies but coding and wave-shaping and you aren't necessarily dealing with sine waves anymore but a set of frequency components.

 

Things have actually moved on past the AN/ALR-94 now. I don't believe from the +/-2deg quote that the AN/ALR-94 actually uses phase interferometry like the AN/ASQ-239 and SPECTRA, and soon, Tranche 3 Praetorian. Phase interferometry based systems are more like 0.1deg accuracy from what I've heard/read. The AN/ALR-94 sounds like a triangulation-based system like Tranche 1/2 Praetorian.

 

I believe this could actually be the technology behind the the EA-18G vs F-22 rumour.

 

http://www.northropgrumman.com/Capabilities/ANALQ218EWReceiverSuite/Pages/default.aspx

 

Passive Precision Geolocation expandable to targeting accuracies

 

Further reading:

 

http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/sig-sort.pdf

 

http://edocs.nps.edu/npspubs/scholarly/theses/2006/Sep/06Sep_Denk.pdf

Edited June 2, 2014 by Emu

[Invader ZIM]

You have a point Emu, but one thing this new type of detection capability requires is huge amounts of processing power and integration to provide warning to the pilot. I don't feel the opfor have that capability just yet. We don't exactly have the capability in our current aircraft it would seem if you go by the reports of F-22's sparring with current generation aircraft.

 

Eventually there will be a counter I'm sure, but processing power as well as more complex variations of LPI techniques are introduced to keep pace with the new passive detection technologies.

 

I'm still a newb when it comes to radar systems, night vision optics is my area of focus, so I'm learning from you guys as well. :D

Edited June 2, 2014 by Invader ZIM

[Invader ZIM]

Thanks for the additional reading and info Emu, fascinating stuff. I actually had the Naval Postgraduate School document about LPI systems and possible means of detection.

 

It appears the US is building on it's experience with LPI and passive detection technologies to help keep ahead of future developments from the opfor. That EA-18G must be amazing in it's capabilities.

Edited June 2, 2014 by Invader ZIM

[Emu]

Thanks for the additional reading and info Emu, fascinating stuff. I actually had the Naval Postgraduate School document about LPI systems and possible means of detection.

 

It appears the US is building on it's experience with LPI and passive detection technologies to help keep ahead of future developments from the opfor. That EA-18G must be amazing in it's capabilities.

Thanks, no problems.

 

As an aside, passive homing/targeting seems to be the next big thing, LRASM has been designed to use it. It's an excellent way to increase detection range without giving yourself away.