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antaress73

Javelin dawn and dusk

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According to many sources, the javelin's effectiveness is greatly degraded at dawn or dusk:

"Infrared crossover is the time at dawn and dusk that the terrain and the target are close enough in temperature to cause the target to blend in with its surroundings. If there is little difference in the amount of infrared energy between a target and its background, then neither the Javelin CLU nor the missile seeker can see the target well, thus greatly degrading the performance of the Javelin. This situation may last as long as an hour, until either the background or the target changes temperature enough to become detectable. - See more at: http://www.darkgovernment.com/news/javelin-fgm-148-anti-tank-weapon/#sthash.2piBo3uM.dpuf"

Is that modeled ? When setting up a battle at dawn or dusk, one could mitigate the effectiveness of the javelin. I bet in a real war the RUssians would attack and try to engage the americans at such times and also use IR limiting contraptions on their vehicules.

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The background, and anything else that isn't generating heat can fade out, because their is no temp difference for the sensor to work with. Rain or fog can make this much worse in just the right conditions. But vehicle engines and weapons discharges make a ton of heat. Even people are considerably warmer than ambient in most climates, most of the time. So it can be a big problem if you are trying to do a recon pass over something that is completely shut down. It almost certainly isn't going to hide much of anything that is trying to move or fight.

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antaress73 and BlackAlpha,

While I can't speak to the Javelin system specifically, I can say that the loss of thermal contrast problem was noted as an issue during the Vietnam War. It was a problem so severe it made whole major steel truss bridges disappear. That said, modern IR sensors and seekers are highly sensitive able to operate on far less IR contrast than were their now ancient forebears, theoretically reducing the problem. At least, somewhat. Here are the specs on a modern Thermal Weapon Sight subject to ITAR and in use by SOCOM.

http://tnvc.com/shop/flir-t70-advanced-combat-thermal-sight-short-range/

dan/california,

Having played TC on a cold rainy day in a bailed NG M48A5, I can assure you a running tank, at least with a diesel engine and pointed at-perpendicular to the AN/TAS-4 FLIR night sight on a TOW launcher, can disappear. I was in the turret, with drizzling rain dripping down my neck from the cracked hatch (vehicle radio nonop, so handheld only), when from a nearby hill (~500 meters, if that), my Hughes colleagues repeatedly lost me altogether from their perch once heavy rain commenced. I was in a reservoir basin, in plain view. On another outing, it was cold, with large patches of fog about. Again, my tank simply vanished from their weapon sight. These issues, though, were caused by emission attenuation via atmospherics, rather than a diurnal occurrence tied to losing insolation and IR reradiation. Nor had this tank fired anything or had a heater going.

Regards,

John Kettler

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I recall (decades ago now) the US was fielding 'decoy tanks' to fool the enemy. I don't know if they still do. Not fancy balloon tanks but simple flat billboards of an Abrams. A poster to stick in a wood line or along a ditch. The 'trick' was to heat up the billboard so it would give off a thermal signature. Testing it during exercises, tankers would swear the vehicle had to be real, going so far as to claim the saw the turret rotating!

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antaress73 and BlackAlpha,

While I can't speak to the Javelin system specifically, I can say that the loss of thermal contrast problem was noted as an issue during the Vietnam War. It was a problem so severe it made whole major steel truss bridges disappear. That said, modern IR sensors and seekers are highly sensitive able to operate on far less IR contrast than were their now ancient forebears, theoretically reducing the problem. At least, somewhat. Here are the specs on a modern Thermal Weapon Sight subject to ITAR and in use by SOCOM.

http://tnvc.com/shop/flir-t70-advanced-combat-thermal-sight-short-range/

Don't know anything about FLIR specs. Could you explain why you think those specs would negate the thermal inversion effect?

I did some searching on google and found some quotes that suggest thermal inversion is an issue for FLIR:

"...thermal inversion that blanks out the Apache FLIR by rendering all temperatures de-pressingly uniform."

http://books.google.nl/books?id=76qUGRiPKpYC&pg=PA121&lpg=PA121&dq=%22thermal+inversion%22+FLIR&source=bl&ots=iLw5Pap30A&sig=Mf3Vvtk_6x361PjOFkq-vCWPxHs&hl=nl&sa=X&ei=QTB9VOKkCISoPYHbgJAP&ved=0CCEQ6AEwAA#v=onepage&q=%22thermal%20inversion%22%20FLIR&f=false

"NAVFLIR

...

Depending on the temperature differentials and wind conditions, a thermal inversion layer normally builds over the water as the evening temperature drops. This inversion layer has been shown to mask the presence of hot objects (boats) on the water, from mid altitudes until thermal conditions stabilize. Exact timing depends on daytime heating, cloud cover and object characteristics, but in general terms there is a temporary thermal washout in 6-5 early evening as the more "reflective" objects transfer from hot to cold. NVGs may aid in target/object detection during these thermal inversions."

http://www.med.navy.mil/Documents/Naval%20Aviation%20Survival%20Training%20Program%20SME%20Website/library/TACAIRNVD.pdf

"9-9. AVIATION URBAN OPERATIONS RISK ASSESSMENT

Risk assessment, as a step in the military decision-making process (MDMP), must identify and assess unique hazards associated with aviation UO. The following list is not all-inclusive, but it provides a good starting point in identifying possible UO hazards.

...

d. Weather.

(3) Night-vision systems are degraded due to city lights and thermal inversion."

http://www.globalsecurity.org/military/library/policy/army/fm/3-06-11/ch9.htm

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I can also personally attest to the thermal inversion crossover effect, even with the latest thermal imaging the army has to offer (to line troops, that is). Multiple time have I been on the OP looking down into a valley and witnessed what is best described as a barrier of cold air that hides everything on the valley floor from view. I've also seen active, moving vehicles blur together with the backdrop environment during the dawn and dusk hours, and when behind terrain features/vegetation in stationary positions (engines still on), become almost invisible to thermal viewers. It's really quite remarkable and makes you realize even today's technology isn't the end all be all we like to think. Take for example smoke screens - something thermal imaging would see through like it wasn't even there - but if you're using WP to produce that smoke screen, the heat given off by the WP burning can produce a very effective thermal smoke screen given the right conditions.

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BlackAlpha,

There appear to be two different, but perhaps interrelated phenomena under discussion here. The one I described is entirely due to normal behavior of materials as solar load is removed and reradiation from the object being sensed becomes dominant. This sort of blanking occurs when the object and the background are temporarily at the same temperature. The other pertains to an atmospheric condition where I'm intimately familiar with one variety, the inversion layer that traps smog, sometimes for weeks on end.

http://www.chaseireland.org/Thermal%20Inversion.htm

My technical argument is that since modern FLIR systems, including detector arrays in IR missile seekers, can now distinguish temperature far more finely than could their Nam era forebears, the period of zero thermal contrast will be markedly shortened, since even a tiny shift in target emission temperature relative to background temperature will immediately make the target seeable again in the IR spectrum. This is opposed to, say, being forced to work with equipment of much poorer thermal discrimination. A system which has the ability to resolve temperature to 0.01C is going to do better in the diurnal transition of thermal contrast than one capable only of 0.1 C. Restating, the more sensitive the detector array, the shorter the period of thermal image blanking.

Regards,

John Kettler

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so I guess that my first post was accurate.. I believe that this is a non-negligible factor and especially on european terrain. Javelin should have reduced detection and accuracy during dusk and dawn battles

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BlackAlpha,

There appear to be two different, but perhaps interrelated phenomena under discussion here. The one I described is entirely due to normal behavior of materials as solar load is removed and reradiation from the object being sensed becomes dominant. This sort of blanking occurs when the object and the background are temporarily at the same temperature. The other pertains to an atmospheric condition with which I'm intimately familiar with one variety, the inversion layer that traps smog, sometimes for weeks on end.

http://www.chaseireland.org/Thermal%20Inversion.htm

My technical argument is that since modern FLIR systems, including detector arrays in IR missile seekers, can now distinguish temperature far more finely than could their Nam era forebears, the period of zero thermal contrast will be markedly shortened, since even a tiny shift in emission temperature will immediately make the target seeable again in the IR spectrum, as opposed to, say, being forced to work with equipment of much poorer thermal discrimination. Restating, the more sensitive the detector array, the shorter the period of thermal image blanking.

Regards,

John Kettler

Ok, but I rather go by what people who have used it say. So I rather believe what SeinfeldRules says. Plus, that fits in with what I've read about the thermal inversion effect. It creates a barrier of air that is of a certain temperate which blocks/degrades the IR signature of objects behind/inside the barrier. I don't see how having more sensitive FLIR can bypass that because the temperature barrier will still be in the way.

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Another thing to keep in mind is that the effect doesn't produce total invisibility - but what could be a well defined tank during the middle of the day becomes a blur that is "lost in the background" and makes identification or target location extremely difficult. Ukraine is not the desert, and there is plenty of intervening vegetation/terrain and background vegetation/terrain that can hide a vehicle. Have never used a javelin, but I could also easily see an infantry man targeting a tank knowing it's a tank, but the CLU has a hard time locking on and identifying the target from all the other thermal radiation.

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John is quite right on the physics.

Their is another wrinkle to the discussion. The degree to which rain and fog block atmospheric transmission is dependent on wavelength. Most sensors till now use a relatively short IR wavelength that is blocked by some atmospheric conditions. Their are longer wavelength sensors somewhere in the pipeline that are much less sensitive to this problem.

It would take solid brass one to commit to an attack plan that could literally be undone by stiff breeze and a break in the clouds.

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Ok. But I think it's safe to say that antaress73's point still stands. FLIR has a tendency to have problems during dusk and dawn, and therefore a Javelin CLU/missile would have problems as well. So, as antaress73 asked, will this be modeled in the game? And if so, what about the other IR equipment/weapons?

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let me put it this way... if you have to attack anyway... why not during a time where enemy sensors/weapons are less effective. Us forces like to use the night against third world enemies because darkness can degrade enemy performance to negligible levels at night and we are not affected.

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dan/california,

This RAND report, R-1694-PR, April 1975, Attenuation of Electromagnetic Radiation by Haze, Clouds, Fogs and Rain, by C. C. Chen specifically addresses the atmospheric attenuation effects of rain and fog on FLIR operating in the 3-5 micron and 8-12 micron bands.

http://www.rand.org/content/dam/rand/pubs/reports/2006/R1694.pdf

BlackAlpha,

Using that as the basis of understanding, we can now turn to FM 3-22.37, the Javelin manual!

http://www.bits.de/NRANEU/others/amd-us-archive/fm3-22-37(08).pdf

There, in Appendix E, p E20, there is an IR crossover chart, and text immediately before it talks about the phenomenon and informs the reader the CLU can resolve a Delta T of 1 degree F. The next page is even more valuable, in that it shows what the CLU display looks like during crossover, as well as what adjusting contrast and brightness settings. The paragraph says something exactly relevant to our discussion. It says the entire target does not experience IR crossover simultaneously; that there will always be a part of the target visible to the gunner as the target goes through crossover. This is because an AFV isn't a uniform IR target. Its components, because of shape, size, material used, internal heat sources and other things, naturally fall into different temperature bands. The pic set at the link, while intended to show the effects of presentation angle as it applies to target ID, neatly depicts what I'm saying. This set unmistakably shows how different parts of an AFV, for that matter any vehicle, are not of uniform temperature. Images are shown with white as Hot.

http://www.globalsecurity.org/military/library/policy/army/fm/3-22-37/e60.jpg

Regards,

John Kettler

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Actually, the manual says multiple times that it can happen that the Javelin may not be able to distinguish a target due to crossover.

"4-59. Sometimes the seeker will not be able to distinguish between the background and the target because the two have the same temperature (crossover)."

- 4-19

"During these two periods, everything in the target scene is about the same temperature, which means there are few, if any measurable ΔTs. As shown earlier, when there is no measurable ΔT, the gunner cannot distinguish a target from its background."

- E-8

The part you quoted at e-21 technically only says that the gunner may adjust the brightness to "locate" a target. But it doesn't specify if you then also can fire at it (will the missile get a lock?).

So, the way I understand this is that during crossover (thermal inversion) you may be able to spot a vague blur using high-end FLIR by adjusting the brightness to the extreme, but you may not be able to identify what you see or fire at it.

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talking of the javelin, i've read that on a forum:

Javelin has two guidance modes... fire and forget and semi automatic command to line of sight.

The first mode is its trick, the second is just the same as most other ATGM on the market with most other missiles offering better range or penetration or speed or a combination of all three.

The fire and forget mode requires an IR signature to get an initial lock so Nakidka or a smoke screen will make that fairly difficult to impossible.

In conventional SACLOS mode it is a horizontal attack missile like any other standard missile and therefore vulnerable to the various defences against such weapons like Shtora, Smoke, and ARENA/Drodz APS.

Very simply as a command to line of sight missile the Javelin needs to be able to track where the missile is so it can detect any deviation from the line of sight and transmit course corrections to the missile. Shtora dazzles the optical tracking of Javelin making its position relative to the target impossible to determine by the guidance system hense it fails.

any comments ? he talks about three countermeasures here: nakidka, which we have already discussed, IR smoke, and shtora ..

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talking of the javelin, i've read that on a forum:

Javelin has two guidance modes... fire and forget and semi automatic command to line of sight.

The first mode is its trick, the second is just the same as most other ATGM on the market with most other missiles offering better range or penetration or speed or a combination of all three.

The fire and forget mode requires an IR signature to get an initial lock so Nakidka or a smoke screen will make that fairly difficult to impossible.

In conventional SACLOS mode it is a horizontal attack missile like any other standard missile and therefore vulnerable to the various defences against such weapons like Shtora, Smoke, and ARENA/Drodz APS.

Very simply as a command to line of sight missile the Javelin needs to be able to track where the missile is so it can detect any deviation from the line of sight and transmit course corrections to the missile. Shtora dazzles the optical tracking of Javelin making its position relative to the target impossible to determine by the guidance system hense it fails.

any comments ? he talks about three countermeasures here: nakidka, which we have already discussed, IR smoke, and shtora ..

I wouldn't call the Javelin the same as other man-portable ATGMs. Correct me if I'm wrong. Judging by what the Javelin manual says:

The CLU locks on to a picture and sends the picture to the missile. The missile then memorizes the picture and tries to fly to where the lock is. It can also somehow figure it out when the lock is moving and the missile can maintain the lock. It uses that method in both the top and direct attack modes. It's fire and forget, it is not SACLOS. The CLU does not send any data to the missile once the missile is in the air.

The CLU or the missile (I'm not sure which) checks the distance to the target. The missiles uses the distance to the target to determine how high the missile should go before leveling out. This happens so that the missile can go as high as possible while still being able to keep looking at the target during the entire time the missile is in the air.

In the top attack mode the manual suggests the missile impacts at an angle of at least 45 degrees. That might be enough to fly closer to a target behind smoke, regain the lock and hit the target. But that's just my wild guess.

I don't know what the maximum angles for the hard-kill APS systems are.

I'm assuming that to create the lock the missile looks for a certain pattern but also accepts small changes to the pattern. I'm guessing that it will lose the lock if the pattern suddenly, drastically changes (let's say a tank changes into something as large as a building or vice versa). I'm also guessing that the missile tries to predict the path of a moving lock and so maybe can also deal with situations where it loses the lock for a short while. But that's just another wild guess.

Fun fact: When you activate the seeker to try to get a final lock (you then get to see what the missile actually sees), you get 4 minutes to get the lock and fire before the battery attached to the missile runs out. You cannot make the battery stop. If it runs out, you need to remove the battery and attach a new one. Then you need to do the final lock sequence with the seeker again.

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BlackAlpha,

The question as posed was whether the gunner could see the target during periods of IR crossover. That's not necessarily the same as whether the missile can. My response was regarding the gunner's ability to see the target, not the missile's.

Regards,

John Kettler

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We do not model thermal crossover for any thermal systems. There are far too many factors involved in determining whether spotting any particular target with a thermal device would actually be affected in a meaningful way. It would be even more wrong to have a blanket "during this time period all thermal spotting is negatively affected" environmental effect.

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Javelin has two guidance modes... fire and forget and semi automatic command to line of sight.

I don't think this is correct; AFAIK the Javelin is autonomous fire-and-forget only; there is no SACLOS mode.

There is "Fastball" attack option, which uses a flatter trajectory and is intended for very short range targets and also certain targets such as bunkers or buildings where a frontal hit rather than a top hit may be more desirable. But it is still automatic fire-and-forget in this mode.

Since the Javelin's guidance system is completely passive (it emits no laser or radio waves or similar that the target can and so "know" it's "on the rails"), and the missile also doesn't fly directly at the targeted vehicle for most of the flight path, the big challenge for an APS system vs. Javelin is simply knowing it's being targeted before it's too late; on an active battlefield it's not practical for an APS system to simply fire at every single projectile in the general vicinity of the AFV.

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I am having trouble with this cross over thing. In principal I get it but a typical day in Europe when will this happen? For example lets take the temperature this August 1st in Nizhyn:

http://www.accuweather.com/en/ua/nizhyn/321998/month/321998?monyr=8/01/2014

High of 33C and a low of 18C.

If soldiers are running around at 36C and tanks are driving around with engines running at 50C or even 40C when is the background ever going to be even close to the temperature of either people or vehicles.

Guide me in a direction that explains how any IR cross over could happen at all in this environment.

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