Requesting "heads up" about Radar ISAR mode as NCTR

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ricnunes

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Unread post13 Jul 2017, 16:30

Greetings,

I'm involved with a discussion on another site (SimHQ) where one of the subjects (which was brought by me) involved the usage of the ISAR (Inverted SAR) mode found on some aircraft, namely the APG-81 in the F-35 as a mean of NCTR (Non-Cooperative Target Recognition).
The other fellow (which I'm arguing/discussing with) basically claims that the ISAR mode cannot be used as a NCTR - and I even searched some info which indicates that ISAR can only identify slow moving target, which would made such ISAR mode unsuitable for NCTR specially against fast jets - but I also remember to have read that for example the F-22's radar, the APG-77 (and by association the F-35 APG-81 radar) can use ISAR in order to perform NCTR or more precisely to ID a radar target aircraft.
However I can't seem to find any source confirming this.

Could someone point me out for such as source? Thanks in advance.
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lbk000

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Unread post13 Jul 2017, 17:36

ricnunes wrote:The other fellow (which I'm arguing/discussing with) basically claims that the ISAR mode cannot be used as a NCTR - and I even searched some info which indicates that ISAR can only identify slow moving target.

based solely on my rudimentary understanding of inverse sar, it sounds like the guy you're arguing with has in mind regular sar instead.

https://cddis.nasa.gov/metsovo/docs/Kar ... 1_8_09.pdf would this help?
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ricnunes

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Unread post13 Jul 2017, 18:03

lbk000 wrote:
ricnunes wrote:The other fellow (which I'm arguing/discussing with) basically claims that the ISAR mode cannot be used as a NCTR - and I even searched some info which indicates that ISAR can only identify slow moving target.

based solely on my rudimentary understanding of inverse sar, it sounds like the guy you're arguing with has in mind regular sar instead.

https://cddis.nasa.gov/metsovo/docs/Kar ... 1_8_09.pdf would this help?


Thanks very much lbk000! :D

Yes I believe that will help, although we can never know about people over the web :wink:
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Gums

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Unread post14 Jul 2017, 03:32

Salute!

Gotta love these threads about sensitive capabilities of weapon systems.

Yes I believe that will help, although we can never know about people over the web


Hate to rain on the party, but there is lot more to NCTR than speed of other guy, paint job, type of motor and so forth.

OPSEC here prolly limits what we can postulate, and I shall not revert to my infamous thread posts concerning nuclear weapons and all the physics plus procedures plus........

Fer chrissakes!! Why would someone post the capability to classify the other guy's plane and such using his/her system? !!!!!!

Sure, there is the "threat" aspect, or the "dare you" mode. "We can see you, and we can tell what you are flying, and our Slammer is about 5 seconds from impact!"

Gotta love it.

Gums sends...
Gums
Viper pilot '79
"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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lbk000

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Unread post14 Jul 2017, 04:40

Silly Gums, the topic is but a vehicle for our autoerotic needs. We get to win an argument and bolster our egos, and that's what matters at the end of the day on the internet, yeah? :D
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doge

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Unread post14 Jul 2017, 14:49

Descriptions about Non Cooperative Target Recognition of F-35. (by Netherlands)
http://www.airdominance.nl/index.php/aircraft-f35.html
The APG-81 radar has a Synthetic Aperture Radar (SAR) function to create high definition maps which can then be used to automatically identify targets on it and it can use Non Cooperative Target Recognition to “Map” out aircraft to identify them or analyze their thrust signature.

It's also in EOTS...? (I'm not sure...)
http://vanguardcanada.uberflip.com/i/304887/0 (page36-37)
And the EOTS underneath the nose of the aircraft provides laser guided bomb targeting, including locking onto moving targets, infrared search and track (IRST), blue-force interrogation, non-cooperative target recognition (CTR) and radar frequency counter measures (RFCM), which allow the F-35 to identify an adversary by the return of its engines and emissions.
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ricnunes

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Unread post14 Jul 2017, 19:56

Thanks very much doge for the heads up and sources :D
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ricnunes

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Unread post14 Jul 2017, 20:11

Hi Gums,

I don't know if I fully get/understand your post but from what I could gather I would say:

- Discussing the fact that an ISAR mode of a radar (this case the latest AESA radars found on the F-35 and F-22 for example) isn't violating OPSEC and even discussing "sensitive capabilities of weapon systems".
Just because we know or discuss the principles behind the ISAR modes and how they work to generate a "NCTR picture" doesn't mean that if he have a Chinese, Russian, <insert your favourite "hostile" nation here> spook lurking these forums or even if I'm that spook that useful information about ISAR and NCTR with ISAR can be forwarded to the engineers of such countries in order for them to develop such systems.

For example, look at the following "stupid example": There are theories about how a Warp Drive (for interstellar travel) would work, however the fact is that no-one in our planet comes close to master the technology in order to develop such device. One thing is knowing the (partial) theory and another completely different thing is to be able to put such theory in practice.
Another example, this one more realistic: I believe most of us knows the basic principles of how a radar work but this doesn't mean that any of us can build an actual radar.

Besides all sources kindly provided by lbk000 and doge and clearly public domain - Anyone can search and find them, including spooks :wink:
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Unread post17 Jul 2017, 11:50

Theoretical background for both ISAR and how it can be used for NCTR are readily available in books, patents and research papers. Many can be found just by googling them. I'm sure China and Russia (and many smaller countries also) have a lot of people who understand the theory very well and even have real world experience with those technologies. Basic principles are quite simple to understand, but the trick is how the actual implementation is done and what capabilities and limitations it has. Those things are definitely very much classified everywhere.

Basically with ISAR a radar generates an image from radar signals reflected from target in pretty much similar way that eye generates an image from light reflected from an object. Naturally that image can be compared to known target types which can be aircraft, helicopters, ships, tanks or whatever. It's easy to see what things are important for radar doing ISAR and using it for NCTR. Radar needs to have very high resolution which is achieved through wide bandwith and very short radar pulses. Short pulses mean low average power, but that is counterd using intra-pulse modulation which means pulse compression is used. In this way average power can be high for longer range but with high resolution of short pulse. High resolution means a huge amount of data needs to be processed very quickly which means very capable computing system is needed. Another thing that is needed is very precise motion compensation systems and methods as motion errors makes images basically more blurry and thus less useful. Also radar signal must be very pure with low noise and radar system must have very low noise in receive path for the same reason.

I agree that your opponent is thinking about SAR imaging which usually doesn't work well against fast moving targets. However there is reason why there is word "Inverse" in ISAR. Basically it reverses the roles of radar and target and works well against even fast moving targets. There can be problems with very fast moving and maneuvering targets if the whole system (both hardware and software) is not well developed.

How ISAR can be used against fast moving targets (a patent): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5492159/

EOTS and other imaging IRST/FLIR systems can definitely used in NCTR. EOTS has the advantage of being tied to most advanced sensor fusion engine available and with multiple advanced sensors in multiple aircraft being connected with high bandwidth, low latency data link. It images in IR spectrum and can definitely create images of the target which can be compared to known target parameters.
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magitsu

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Unread post17 Jul 2017, 12:41

I wonder how much this multisensor threat library building and formulating images / comparing them to the library entries differs when we switch from air to naval realm. Still acoustics, but with different kind of noise sources.

I mean for example the Finnish naval mine 2000 supposely relies on this. Prebuilt threat library and then choosing targets which match the set threshold for valuable targets. Page 16 (chapter Alussignaalikirjastoa...) in Fnnish here: http://www.rannikonpuolustaja.fi/archive/2001_3.pdf
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ricnunes

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Unread post17 Jul 2017, 14:22

Hi hornetfinn,

Thanks for your heads up and link :D
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armedupdate

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Unread post26 Jul 2017, 08:53

Does ISAR get rid of the "tight enough radar resolution cell to distinguish two targets problem"? I heard somewhere here that radars due to doppler effect in order to find to targets, they need to sweep and get them each within beamwith. Can ISAR shine the light on them both at the same time and generate two pics for a fire solution, or does it have the same limits?
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hornetfinn

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Unread post26 Jul 2017, 09:24

armedupdate wrote:Does ISAR get rid of the "tight enough radar resolution cell to distinguish two targets problem"? I heard somewhere here that radars due to doppler effect in order to find to targets, they need to sweep and get them each within beamwith. Can ISAR shine the light on them both at the same time and generate two pics for a fire solution, or does it have the same limits?


It doesn't, but the resolution cell in ISAR can be so small in modern radars that it's much less of a problem. Long range and small, fast and agile targets can be a problem though. It's the matter of signal processing and software to distinguish two or more closely separated targets. ISAR is a mode for target recognition/identification and is not really suitable for generating fire solution. It images the target using radar frequencies but it doesn't measure target heading, speed or other such things important for fire solution.
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Unread post27 Jul 2017, 03:25

What is the typical size of radar resolution cell at BVR ranges for modern AESA radars? Older radars?
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Unread post27 Jul 2017, 09:22

armedupdate wrote:What is the typical size of radar resolution cell at BVR ranges for modern AESA radars? Older radars?


Well, that depends a lot on radar type, exact radar mode in modern radars) and also range. For SAR and ISAR it can be very small and be measured in centimeters (or inches) rather than in meters in modern AESA radars (depending on range and how large area is under surveillance of course). This is because the synthetic aperture can be very large compared to real physical aperture. Older radars usually had SAR resolution cell measured in meters to tens or even hundreds of meters.

For BVR air combat modes there is usually no need for extremely small resolution cells as other considerations are more important (like scanning speed, update interval and multi-target tracking). There we are likely talking about meters to hundreds of meters in range resolution usually. This depends on the bandwidth of the radar and modern radars can have much better resolution than older ones due to higher bandwidth available. The azimuth resolution depends on the beamwidth and range. Modern fighter radars have beamwidth somewhere around 1.8-5 degrees depending on radar antenna size and efficiency. Large AESA is way better than small MSA or PESA radar. That would mean azimuth resolution is usually several kilometers in 100 km range. There are ways to improve this and determine if there are more than one target present. This involves focusing more time and radar energy towards selected track(s) and processing the received signals to determine whether it's just one target or many.

So range resolution cell 100 km away is usually something like 10 to 1000 meters in range and 3-10 kilometers in azimuth. More modern radars can have smaller resolution cells and can use more advanced methods to determine number of actual targets in a group. So two or more targets flying abreast towards the radar will look like one target even when spacing is hundreds of meters. This assuming no advanced processing and methods are used. ISAR is definitely one good way to find out that there are multiple targets present.

You can read about the theory for example from this online book: http://www.radartutorial.eu/druck/Book1.pdf
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