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Laser threat defence

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Laser threat defence

Old 17th Feb 2016, 11:59
  #21 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
It definitely behaved like a handheld [email protected]
Really.

And how do handheld [email protected] behave? Do they have good table manners?

If you were at FL360 and flying straight & level then the source must have been at least 14 miles away, and even on a remarkably clear, undercast-free day that's one heck of a [email protected]

PDR
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Old 17th Feb 2016, 12:05
  #22 (permalink)  
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Yes, really. I'm sure you're clever enough to work out the difference between a hand held [email protected] and a stabilised [email protected] And 14 miles? No.

I note that you ignore the more serious incident and my first question to you.
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Old 17th Feb 2016, 12:33
  #23 (permalink)  
 
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In this day of precision guided weapons, surely a detachable device could ride the beam back down to the source.

Perhaps a javelin type implement with GPS. Pin the bastards to the floor until the cops arrive!
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Old 17th Feb 2016, 12:48
  #24 (permalink)  
 
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In the spirit of hopefully good humoured and constructive exchange of views, I think PDR1 you are guilty yourself of not thinking things through regarding pointing at stars....or was your comment about 9.4 years an attempt at humour? [email protected] pointers are advertised for this purpose, what they reflect on (presumably something in the atmosphere) someone more knowledgable can no doubt tell us.

Your maths and experience give the debate more substance, but some of your assumptions regarding waggling do not fit with my perception. I may be incredibly unlucky, but I have been targeted many times and it certainly seemed for longer periods than you are suggesting is possible. Just humour me....if these idiots can target the beam reliably (I know you think this unlikely) at what range does your maths suggest it becomes dangerous with the 90mW green [email protected] we discussed earlier?

Your last post went some way to convincing me on the 8000 foot case, but I missed a step explaining why the 300 foot case needed to be divided by eight, probably me, but I missed your logic.
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Old 17th Feb 2016, 13:10
  #25 (permalink)  
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Originally Posted by Chesty Morgan View Post
It definitely behaved like a handheld [email protected]

I didn't really care who was holding it at the time though.

Bringing a bit of maths in myself.

If you were at FL360, let's say that you were impacted at 45 angle below the horizon, as from directly below you wouldn't enter the cockpit. So from surface, that's about 15km in a straight line.

Firstly atmospheric losses would need something rather bigger than the 5mA handheld I use in a lecture theatre. When I've played with it on a clear day, a few km is all that works at.

Secondly, you were flying I'd guess at around M=0.75, that would map to a groundspeed of about 220m/s. Side on then, to track you, that would need some device that moves the [email protected] at a rate of about 0.8 degrees/second. Achievable, but would require some kind of aiming and tracking device - say a rifle sight attached to the [email protected], mounted on the top of a tripod.

Let's say that the tracking is achievable to a steadyness of 1%: I suspect that this would actually be pretty good. At the aeroplane, that would map to a back and forth wobble of 2.2m: or a couple of times the size of an aircraft side window. In practice, it probably wouldn't be that good and probably back and forth nearer the length of the aeroplane is more likely.

My guess then is, that from where you were sat, that would look very like a wobbly handheld device when, in reality, it was incredibly steady.

G
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Old 17th Feb 2016, 13:17
  #26 (permalink)  
 
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As I am having a rest (not a ban) from the other thread...

As others have pointed out, optical filters to cut red or green [email protected] light will also affect the visibility of aircraft navigation lights, and ground based lighting. So it is effectively impossible to block [email protected] light while still allowing a pilot to keep an unimpeded visual look out.

However, reflected [email protected] light can be just as damaging as a direct hit, the pilot doesn't need to be looking out the window, a reflection off an instrument could be just as bad.

My suggestion would be for antireflective coatings to be applied to all cockpit glazing and for other materials in the cockpit to be dark or light absorbent matt colours and finishes wherever possible. Micro scratches on the outer surfaces of the cockpit screens also cause issues when back lit by bright light. A hardened coating or polish capable of surviving the rigours of flight could be used to try and smooth out these scratches.

These suggestions wouldn't stop a direct [email protected] hit, but by eliminating reflections the dazzle effect in the cockpit could be reduced significantly.

Alternatively, pilots could take to wearing Raybans 24/7. Wouldn't do much to cut down the [email protected] light, but they would look cool. On a serious note, dark glasses would likely make the problem worse because the eye pupils would be open wider. One of the reasons daytime [email protected] attacks are seldom reported is that the pilot doesn't even notice them against a daylit background, although eye damage could be being caused and going unnoticed.

Interesting figures on the strength and spread of beams from the ground. The first 6000 feet of air above ground is stuffed full of dust, moisture and other particles and attenuates [email protected] light considerably. If a beam is aimed straight up, it appears to cut off rather abruptly after a rather short distance. This is where the quantity dust in suspension from the ground diminishes. As the beam is swung down towards the horizon, it appears to lengthen. This effect is due to the dust being illuminated by and refracting and attenuating the beam. In clear air, a 200mW green [email protected] has a naked eye visible range in excess of 80 miles (demonstrated to 84 miles between mountain tops). At sea level altitudes a range of 10 miles is more likely. A 200mW [email protected] will cause instant and permanent eye damage at ranges of less than a couple of hundred yards. The potential for permanent vision loss diminishes with distance. At a mile or so, the blink reflex and beam spread will prevent permanent injury, although the dazzle effects will be severe and vision will probably be affected for several minutes.

As for an outright ban on [email protected]? Well the average household has at least five fitted to domestic entertainment systems, CD and DVD players, [email protected] printers, [email protected] levels, [email protected] pointers, etc, etc. These things are not going to disappear.
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Old 17th Feb 2016, 13:44
  #27 (permalink)  
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Ghengis, on the other hand it could've been somebody getting lucky with a powerful handheld.
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Old 17th Feb 2016, 14:08
  #28 (permalink)  
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Originally Posted by Chesty Morgan View Post
Ghengis, on the other hand it could've been somebody getting lucky with a powerful handheld.
Hellishly lucky!

The longest lens on my camera is 1200mm, which will fill the frame with a large aircraft a mile or so away. It's not much short of a miracle if I can keep tracking an aeroplane accuratelyat anything much beyond that - and that has a viewfinder, and I've been taking photographs like that (and before that was a pretty good rifle shot on the range) for several decades.

G
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Old 17th Feb 2016, 14:46
  #29 (permalink)  
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I repeat, you do not need to track an aeroplane.
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Old 17th Feb 2016, 15:14
  #30 (permalink)  
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I don't mean track electronically, I mean use some device to follow the aeroplane's track.

I can track an aeroplane with my camera, or a rabbit across a field with a rifle.

G
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Old 17th Feb 2016, 16:02
  #31 (permalink)  
 
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One thing PDR is missing is that up-collimators have been shipping on high end [email protected] pointers for a long time. The two milli-Radians he uses in his example are a low end toy at this time. Its easily possible to achieve 0.1 mR with a few external optics.


[email protected] pointer companies like to cater to their mainly teenager and 20-something customers, and those customers are often into "burning", ie seeing what they can burn with a focused beam, Power, which equates to the teenage desire for more horsepower in muscle cars, and Distance. Distance is becoming more and more popular, which is a problem.


When we do [email protected] in Airspace Calculations, we look not just at the Nominal Ocular Hazard Distance, but the Sensitive Zone Exposure Distance and the Critical Zone Exposure Distance. CZED and SZED are more about what pilots need to worry.


This is not just about [email protected] shows accessing airspace legally, there are Lidar Systems, and [email protected] Guide Stars for astronomy, and [email protected] Wind Profilers. The cloud height sensor at most airports is a pulsed infrared [email protected] of very low power. There are also [email protected] based glideslope systems for a variety of applications, including some that are directly visible to the pilots eye (Those are intrinsically safe, btw)


So lets start with NOHD. NOHD is a statistical likelihood that there will be large, observable damage to the retina for a visible [email protected] Not all retinal burns readily show up in basic ophthalmic testing. It usually takes a retinal profiler to detect small damage, and those machines do not grow on trees. The famed Amsler grid referenced earlier pretty much only shows large scale or very severe [email protected] injury to the eye.


For the record, it is often possible to discolor the proteins in the back of the retina and do damage that heals, as well as permanent damage.
So each case must be evaluated on a case by case basis.


A quick approximation for NOHD in feet for a continuous wave [email protected] is


NOHD = (32.8/theta ) times the Square Root of (( 1.27 * average power)/0.00254)) Where theta is the 1/e divergence of the [email protected]


1/e Divergence is basically the 10% and 90% points in the power distribution curve across the beam in the [email protected] This curve is most often a Gaussian distribution, although cheap [email protected] pointers often have horrible beam profiles, most of the high power green pointers are starting to ship with much better beam quality.


So lets move away from the damage threshold, which is a probability of damage occurring, not a absolute guarantee that there will be damage if you observe a beam that is over the NOHD. After all these beams are moving, and greatly disturbed by atmospheric turbulence.


Next Post, CZED and SZED.


Steve
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Old 17th Feb 2016, 16:53
  #32 (permalink)  
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I know! You don't need to do that.
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Old 17th Feb 2016, 17:53
  #33 (permalink)  
 
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I dont think "anti [email protected]" coatings to windows or glasses work by pilots would be practical. Ones that would work reliably would have lenses so dark, you would inhibit normal vision.

A reflective (partially mirrored) coating to the inside of windows would work better. It wouldn't be 100% effective, but would provide a measure of assistance.
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Old 17th Feb 2016, 17:58
  #34 (permalink)  
 
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I got my start in [email protected] doing [email protected] shows. The low cost [email protected] pushed many of us who had professional gear, who obtained the required permits, and insurance for outdoor shows out of business. Most of those low cost [email protected] users are totally unaware or ignoring the fact that they need permits for un-terminated [email protected] shows in airspace. Filing the paperwork generates NOTAMs, and there is a lot of math required to ensure safety compliance. That means that the companies who still try to be legal must turn down a lot of potential customers, as there is a delay, and mandatory review period with the local agency.
Indeed. The sudden availability of low cost easy to use [email protected] has been a double edged sword to the [email protected] industry. Many promoters seem reluctant to spend proper money on a well run, safe show, when they can buy something cheap, nasty and dangerous off ebay for far less.

If Sim is who I think he is, his knowledge on the subject of [email protected] is quite legendary.
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Old 17th Feb 2016, 18:24
  #35 (permalink)  
 
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Back to the OT...

I was zapped by a [email protected] at night a few months ago whilst downwind to a major airport.

Fortunately recognising what was going on, control was handed over to the other guy, whilst looking away from the source.

It seems that an ability to pull over a completely blacked-out blind on the side windows would be a better solution than anything we have at present.

It is less likely that someone could be dazzled through the front windows unless the beam is directly in front, such as during final approach.

Notwithstanding trying to pinpoint, apprehend and prosecute the perpetrators, are the aircraft manufacturers looking at this, since this is becoming a more frequent occurrence?

What are the regulators doing?
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Old 17th Feb 2016, 18:50
  #36 (permalink)  
 
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Without going into details that may help the bad guys, I think you need to take a look at the actual beam parameters from a moderate cost 1 watt [email protected] pointer. Your required [email protected] power estimate for damage at higher elevation is off to the high side by a huge factor..
Well I took my numbers from BS-EN60825 (aka " IEC60825"), the recognised standard for [email protected] safety. Specifically the "Maximum Permissible Exposure" (MPE) data it contains, as summarised in this graph:



[this is the wiki version which has the plots in colour so they're easier to see]

Now it's worth noting that "MPE" is defined as "The highest power or energy density (in W/cm2 or J/cm2) of a light source that is considered safe, i.e. that has a negligible probability for creating damage", and the typical value it produces is 10% of the dose that has a 50% probability of creating damage in the 95th percentile population (by sensitivity to [email protected] injury), and includes all eye damage modes (corneal, retinal etc). So it's actually well BELOW the value that would be certain to cause damage - exposure AT this level is actually deemed "safe". So where does your suggestion that I'm underestimating the number by a factor or 10 come from? I've given traceable, authoritative sources - what are yours?

PDR
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Old 17th Feb 2016, 18:56
  #37 (permalink)  
 
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PDR, you seem to be hooked on actual damage to the eye rather than temporary blinding/light spots and distraction.
Am I? is that why I explicitly talked about this at the end of the post immediately above this one of yours?

PDR
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Old 17th Feb 2016, 19:05
  #38 (permalink)  
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Yes, and further you talk about aimlessly waggling at 60 degrees per second. Why don't you consider a more concerted waggle in the general direction of the aeroplane with the intention of actually hitting it.
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Old 17th Feb 2016, 19:06
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One thing PDR is missing is that up-collimators have been shipping on high end [email protected] pointers for a long time. The two milli-Radians he uses in his example are a low end toy at this time. Its easily possible to achieve 0.1 mR with a few external optics.
Indeed it is, and while that significantly increases the power density in the beam by a factor of 400 (remembering that the analysis suggested we were 3-6 orders of magnitude below the MPE value) it also reduces the size of the beam for the 8,000 foot aeroplane from a 10m disk to a 50cm disk, and the probability of that disk illuminating the pilot's eyes (the required targeting accuracy and/or the duration of illumination for a "waggle" swipe-pass) become much more significant, so it doesn't change much. For the aeroplane on finals at 300 feet the 0.1mRad beam diameter drops to about a quarter of an inch. Are you really suggesting that a person standing 600 feet away with a [email protected] pointer can hold a 1/4" diameter beam onto a pilot's eye, when he probably can't even SEE the pilot through the cockpit window?

But I am also led to believe that the sort of [email protected] used as toys by idiots aren't the ones with particularly effective collimators fitted to them, although the source for that isn't particularly authoritative.

PDR
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Old 17th Feb 2016, 19:08
  #40 (permalink)  
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He wouldn't need to "hold" it on the eyes.
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