h a l f b a k e r yPoint of hors d'oevre
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It seems that idiots shining laser pointers at airplanes is a significant
problem for pilots these days, to the extent that the FAA is offering a
significant reward for information leading to the arrest of any morons who
are out there doing it. Apparently some of these lasers are so bright they
can
cause physical damage to the eyes of pilots—I heard a story this morning
about a pilot who needed to have his cornea scraped as a result of such an
attack.
Clearly, this needs to stop, or at the very least pilots need to be protected.
To the latter end, you could use a video display that covers the cockpit
windshield. But if the display were to fail, you'd have to be able to fly on instruments alone,
so you'd need to be able to easily remove the display.
The display would thus consist of a retractable screen and an ultra short
throw projector mounted above the screen. The screen slides across the
windshield and latches in place with an electromagnetic latch. If the
projector fails for some reason, the latch is automatically released and the
screen retracts. Conversely, if the screen is retracted manually, the
projector cuts out so as not to reflect on the windshield glass.
The display is fed from a camera mounted on the nose. At least if the
camera is blinded, the pilot's eyes aren't damaged. Additionally, heads-up
information can be added to to the display for the convenience of the pilot.
Laser briefly blinds police helicopter pilots
http://articles.gle...ser-glendale-police
“After being struck by the laser, Robertson was taken to a nearby hospital, where doctors scraped his corneas.” [ytk, Feb 13 2014]
Article with video of press conference
http://ktla.com/201...against-aircraft-2/
About 15 seconds into the video [ytk, Feb 13 2014]
Localized Glare Control
[xaviergisz, Feb 18 2014]
[link]
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Before anyone brings it up, it turns out that depth
perception is relatively unimportant in flying. Most
objects that you see are so far away that it doesn't
really apply. Simulators don't provide for depth
perception and they're perfectly usable, and anyway
there's nothing stopping a one-eyed
person from becoming a pilot as long as he or she can
demonstrate that such a disability doesn't interfere
with the ability to fly. |
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//Given that laser pointers emit infrared laser
light// |
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Uh, no they don't. That's why they're used as laser
pointers. An IR laser pointer would only be good if
you were lecturing to a bunch of pit-vipers. |
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In theory, you could give the pilots goggles that
had filters specific for the fairly narrow bits of the
spectra that red or green pointers fall in. |
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Or just get them to close one eye on approaches. |
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The risk of actual eye _damage_ from any common
(ie, less than 1W) laser at distances over a few
hundred feet is negligible - the beam won't be
perfectly collimated, nor aimed at the pilot's pupil
with any steadiness. The report of a pilot having
to "have his cornea scraped" doesn't make sense. |
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1 and even 2 watt laser pointers (well, handheld
diode lasers) are getting more and more common. In
the US, they're required to have a lock (the one
source I found quickly had a code lock), but that
doesn't prevent deliberate misuse. And collimation
on the 2W is less than a tenth of a degree. |
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In that range you're talking about at least flash
blindness from even momentary exposure up to a km
or so. |
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//The risk of actual eye _damage_ from any common
(ie, less than 1W) laser at distances over a few
hundred feet is negligible - the beam won't be
perfectly collimated, nor aimed at the pilot's pupil with
any steadiness. The report of a pilot having to "have
his cornea scraped" doesn't make sense.// |
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Well, that's what this article from 2010 says (link),
and I have no particular reason to think it's inaccurate. |
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// // laser pointers emit infrared// no they don't // yes they do; they frequency double IR to get the colour then let the leftovers escape to avoid heat buildup. |
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So a coating on the cockpit glass which reflects the exact wavelengths. Assuming such coatings exist. Doesn't sound cheap. |
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Most laser pointers are not frequency doubled.
They are usually direct diode lasers. And even if
they were, the emission (meaning what actually
comes out of the business end) isn't IR. |
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And the cost to coat an aircraft windscreen in a
multi-point narrow band blocking filter would be in
the thousands of dollars range. Maybe the low
10's, but not much more. This is based on the
price of coating significantly smaller lenses, but
they scale reasonably linearly. Given the number
of different lasers out there, however, blocking all
of them will significantly interfere with vision.
Finally, finding a coating that will work and not
degrade on a polycarbonate windscreen is going to
be difficult. |
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//narrow band blocking filter// stacking a whole
bunch of band pass filter on the windscreen would
lead to really sucky transmittance... |
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Re. the article, frankly I don't believe it.
Seriously, if the guy was dazzled by a laser (i.e., it
hit his pupil) which was also powerful enough to
burn his cornea, his corneal burns would be the
least of his problems - he would have permanent
retinal damage. |
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I also don't believe that any laser less than several
watts (which is a fairly serious laser, not a laser
pointer or even a hacked BluRay laser) is going to
burn a cornea at distances of hundreds of feet or
more. The beam (which would have to be
incredibly well collimated, by the way) is not
going to remain fixed at one point on the target
for more than milliseconds. Enough time to
dazzle; possibly enough time to damage the
retina (unlikely, to be honest) but not enough to
"burn" a cornea. |
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So, I suspect that the Glendale News (trustworthy
though it may be on optomedical matters) has
made a mistake in this instance. |
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But, regardless, a regular laser pointer (even
including the cheap Chinese ones which are often
well over the stated milliwatts of power) is going
to dazzle pilots, not cause permanent damage. |
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//So, I suspect that the Glendale News (trustworthy
though it may be on optomedical matters) has made
a mistake in this instance.// |
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Direct quote from the pilot: “I was immediately taken
to the hospital, where what they did was scrape off
the top layers of my eyes, which I can assure you is
extremely painful.” |
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There's even a video of him making this statement at
a recent press conference, which is how the story
came to my attention (link #2). |
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I obviously can't vouch for the veracity of his statement (or the medical necessity of the
procedure in this instance), but his claim is definitely that he had to have his corneas
scraped following a laser attack. |
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//stacking a whole bunch of band pass filter on the
windscreen would lead to really sucky
transmittance// |
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They can block more than one band per filter (the
one we use at work has a secondary blocking range
to keep out stray light from a distance sensor), but
I'm not sure what the upper limit is, and you're
talking about like 15 or so bands that need to be
blocked. |
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//and you're talking about like 15 or so bands that
need to be blocked// |
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Personally, I vote we start with The Black Eyed Peas
and Tom Petty. |
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[ytk] Well, I'm sure he thought they were scraping
his corneas. Both of them? And yet the laser that
burned both his corneas did no permanent
damage to his retina? Nah. Someone somewhere
got something wrong. It happens. |
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But that is beside the point. My point was that
the sort of lasers that the average moron is likely
to have access to are not capable of doing damage
to the eye of a pilot several hundred or more feet
away. A regular laser pointer is even less capable
of doing harm. Dazzling (which can last seconds
or minutes), on the other hand, is a serious risk. |
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See my above anno on what's available on the
market. You're looking at a 2W beam with a diameter
of about 3cm at 1km. Full, direct sunlight is .1
W/cm^2, that beam intensity is .28. You don't think
that could present a serious distraction, and possibly
real harm if it happened to stay on the eye for any
length of time? |
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//You don't think that could present a serious
distraction, and possibly real harm if it happened
to stay on the eye for any length of time?// |
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A serious distraction, and dazzlement (lasting for
seconds or minutes afterwards) yes, definitely. |
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Permanent damage - no. You can (though it's not
advisable) look at the full sun for seconds; you'll
be unable to see much for many seconds (up to a
minute, maybe) thereafter, but your eyes will
recover just fine, as long as you don't do it dozens
or hundreds of times. |
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Your laser delivers three times the power, but
natural blink and aversion reflexes mean you won't
be exposed for more than about 1/20th of a
second. |
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So yes, it will dazzle badly and impair vision for
seconds or minutes thereafter, but it won't cause
permanent damage. |
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The maximum permissible exposure to laser radiation is
apparently 2.5*10^-3 W/cm^2 for a duration of .25
seconds. Given the .28 figure provided by [MechE], the MPE
would be exceeded after 1/448 second of exposure. Even a
reaction time of 1/20 second would yield an exposure of
over 22 times the MPE. |
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I don't honestly know how conservative these safety
guidelines are, or how the likelihood of permanent damage
scales as you exceed the MPE, but I do know that a laser
with more than 5 milliwatts of power is capable of causing
permanent eye damage, so I don't see how you can dismiss
it as impossible that a laser with an effective power 280mW
could do so as well. |
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The only simple solution I can think of would be mandate
that all laser pointers emit right circularly polarised light.
This would be relatively simple since most lasers emit
linearly polarised light, so only a quarter-wave retarder
would need to be added. |
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All cockpit windscreens would be coated in left circularly
polarising filter; any laser light shining at the cockpit
would be almost completely attenuated. |
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A similar proposal for headlights and car windscreen was
also made (this problem has been mainly addressed with
high-beam & low-beam headlights). |
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// I don't honestly know how conservative
these safety guidelines are,// |
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They are very conservative. Put it another way:
they make looking at the sun for 1-2msec out of
bounds. Certainly, it's not advisable to look
directly at the sun, but if you do (with the naked
eye), an exposure of a second (or even many
seconds) will not cause permanent damage. |
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I'm not sure how much this modifies the equation, but if a laser dazzlement attack occurred at night, it is likely that the pilot's pupils would be much more dialated than during the day when one might have a chance to look at the sun. |
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Of course pupil dialation wouldn't have any impact on cornea damage, but I agree completely with [Max] that cornea damage from a distant laser without retina damage sounds very unlikely. |
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I was told of someone who was sent to the cardiac unit after his finger was badly burned by a car battery shorting through his ring - on the grounds that the incident involved electricity. |
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Perhaps the doctors made a similar over-generalisation here. Exposure of the eyes to welding light damages the corneas; lasers are also light; therefore we need to treat the patient for corneal burns. |
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I would suggest using something akin to the screen on an auto-darkening welding helmet - which would detect the bright light and very rapidly turn opaque. |
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At the same time, the system could switch over to a backup display by clever implementation of a projector which would switch on and display an image-enhanced, heavily filtered or even just infrared display from forwards pointing cameras would work well. The transition could be very rapid and the backup image would be nearly instantaneously put up. |
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Why can a simulated image not be projected on the windshield itself with any high intensity light source filtered out?
The dang things practically fly themselves now anyway, and auto-darkening could possibly be used to cause crashes if a pilot were landing using hand-eye coordination alone. |
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Mount your own laser on the airplane and shoot it in the direction of the incoming laser to destructively interfere with it. |
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