FBI Investigating Laser Beams Pointed at Aircraft 500
sakshale writes "In an earlier discussion about Laser Pistols, many people argued about the concept of using them to target pilots of airliners. Apparently the FBI is investigating incidents in Cleveland and Colorado Springs. They issued a warning on December 14th."
Green with envy (Score:5, Informative)
Given some time, and--right or wrong--somebody will attempt to pile on the regulations and we can forget about buying green lasers from ThinkGeek [thinkgeek.com] or anyplace else.
Yes there are some (Score:5, Informative)
That would hurt.
Re:Questioning this... (Score:1, Informative)
Re:Questioning this... (Score:5, Informative)
Re:Hmm. I dunno. (Score:3, Informative)
But I've been on many a looping approach where the plane is banked substantially to one side or the other for a good minute or so, during which I'm looking down, at a steep angle, right into business districts, neighborhoods, etc. If my eyes can see the ground, the ground can see my eyes.
Re:Why green? (Score:5, Informative)
Lasers for display are regulated by the Center for Disease and Radiological Health. Your not supposed to direct a laser above 5mw up into the sky.
At a long distance, the beam definitly becomes incoherent. Gas lasers are considered better than solid state in regards to beam colimation, and without optics my 2.5' long argon tube beam ends up 1' or more wide at a distance of only 1000 feet or so.
Targeting, no... Someone might manage to cross the planes path, but in order to track a plane I'd iamgine you would need to build a box filled with dirt sitting on innertubes to isolate vibration, then come up with a servo mechanism. I don't think 16 bit DACs would give enough accuracy with glavos.
Weapons targeting systems do not use visible lasers AFAIK. It would be a giveaway if there was a bright green dot on the target and a green line tracing back to the source.
Also, laser light is different then searchlights because the light is polarized. So you can see the beam better from one way versus the other.
Happened to me (Score:4, Informative)
One note; there was mention in the news of a quote from an FBI agent who said it had to be a sophisticated laser to track a plane for severla seconds at 8500 feet. I disagree. I believe with a braced or tripod mounted unit in combination with the beam divergence holding on target for a few seconds is easy.
Re:Questioning this... (Score:3, Informative)
8,500 feet straight up is more than a few thousand feet at enough of an angle that you could be in line of site of the pilot.
I strongly doubt that this was a hand held laser. At about 10,000 feet - 2 miles - that would take a pretty steady hand and damn good eyes.....
Re:Questioning this... (Score:3, Informative)
now I dare you to hold that beam on a basketball that is 1500 feet away. you CAN NOT. it is impossible without special equipment. even a tripod and scope is inaccurate and will jiggle all over hell from ground vibrations. there is no way you can hit an airplane a "few miles away" with anything a consumer can touch.
the only thing useable is gyroscope stabalized laser aiming systems. and those are not common, cheap or easy to get.
There is one way I could nail a plane very brefily with a laser. a 12 inch dobsonian telescope with the laser perfectly aligned to correspond with the crosshairs of a guide eyepiece and at least 1 watt or more and perfeclty collimated for that distance.
now tell me where I can get a very light 1 watt laser with military grade collimation...
Re:Questioning this... (Score:5, Informative)
Ever look at a plane several miles away that is coming straight or almost straight in your direction? Sometimes it seems like they aren't moving at all. The number of arc seconds they will move in 10 seconds time relative to you is very small. I don't think a gyroscope/mechanical tracker would be necessary.
Re:Why green? (Score:1, Informative)
In Real Life there's dust and water vapor in all air, and a powerful laser does show the whole beam.
Re:Green with envy (Score:5, Informative)
I have the impression you doint know what a 100 mW or a 300 mW laser is?
Standard laser pointers are made to divergent, the outlet of the beam has usually a small drop of plastic or glass to achieve that.
A 100mW laser easily blinds you. And if you have bad luck it does so permanently (usually only the parts imediatly hit, that is ~ a millimeters in diameter, but can be more).
A 300mW laser easily cut plastics, paper, wood etc. The lasers sold here http://slashdot.org/article.pl?sid=04/12/28/18532
You probably have a key missconception: lasers usually do NOT divergent (or only a very little), thats exactly what makes a laser different from normal light.
angel'o'sphere
Want to hit that cockpit with your LASER? Easy... (Score:3, Informative)
"Speed of motion" (as opposed to actual velocity) is apparent. When the aircraft is coming toward or away from you, it's speed of motion is less than if it was passing side to side. Just get in line with the sucker as it lines up on approach. Fire toward it.
Rifle fire has brought down military jets with this technique. It's as old as the first biplanes, and still works.
Chances are pretty good that you can do this with a proper rifle scope and a small hand LASER. As far as brightness goes, remember, the LASER (even at five milliwatts) is focused tightly. The beam is usually also parallel to a good extent. I can verify that at five miles on a bright day a five milliwatt LASER is the brightest thing on the horizon IF YOU GET LINED UP WITH IT.
Re:WARNING: (Score:3, Informative)
Re:Green with envy (Score:3, Informative)
What makes a laser different from normal light is that it is coherent and monochromatic.
Uncollimated laser light obeys the inverse-square law. Even collimated laser light obeys it, it's just that you need to treat the initial range to the source as greater than it actually is - the 'source' of the beam isn't the exit lens, but is represented as a point behind that lens. The more collimated the beam, the further behind. Ferinstance, using numbers pulled right from my butt, if the beam divergence is 1 mrad, and the beam diameter at the exit lens is 1 mm, then the effective source of the light is a point one meter further away than the exit lens. If you then measure the beam intensity at 5 cm and 10 cm from the exit lens, it won't look like it's falling off as the inverse square, because the beam only widened by about 9%. But really, you didn't double the distance, you only increased it from 105 cm to 110 cm.
Re:Green with envy (Score:2, Informative)
Snipers use a visible red dot, of course, since they have to see it (at least old school snipers).
Me:
Snipers in movies use a visible red dot.
Real snipers use passive optical sights - that is they don't send a signal to the target, they passively collect data (light [visible or IR]) from the target. Old school snipers use iron sights with high quality Mk 1 Eyeballs.
A physicist's perspective (Score:5, Informative)
It is quite possible to damage a pilot's eyes at a range of a few miles, using only commercial laser systems [bigskylaser.com]. If done by competent individuals, it would probably involve a pulsed infrared laser (harder to detect, and the eye is more susceptible to near IR than to visible). A Nd:YAG laser (1064 nm) would be ideal.
Since a pulsed laser is used, there's no need for tracking the plane. A single 10-nanosecond pulse would be sufficient. At 10 - 20 pulses per second, you could just scan the sky in the area of the plane.
After reading the story, I did some rough calculations. For the above-mentioned laser, the laser beam would do damage (although likely not sufficient to totally blind the pilot) at ranges of up to two miles, and the beam would have a spot size several meters in diameter at that range. Obviously, with additional optics, range and spot size could be changed.
It seems to me that the laser could simply be mounted to a scope on a tripod (after some careful alignment), and that targetting by hand would work at least some of the time.
All this aside, I don't think the recent cases are anything to be worried about. More likely it's just a nutbar with a relatively weak visible laser (I assume the laser was in the visible range because the pilots reported it, and I doubt commercial planes are equipped to detect IR lasers). If it was someone serious, they'd be using IR lasers, and we wouldn't know until pilots started getting eye damage.
That said, the overall risk of plane crashes from this form of attack is low. If the airport and immediate area are kept secure (and they should be if only to guard against Stinger-style missile attacks), it's very unlikely someone with a commercial laser could get close enough to completely blind a pilot. Military or custom-built research lasers could blind from greater distances, but such systems are very finicky, and I can't see terrorists pulling that off.
Finally, I'd like to address a few points other people have brought up. If the polarization and angle of the beam are chosen correctly, virtually none will be reflected off the plane's window, and all will be transmitted (see Brewster's Angle [wolfram.com]). For modest laser powers, the damage to the retina will be localized to where the laser beam is imaged, leaving much of the pilot's vision intact. Bad for the pilot, but he could probably still land. For more intense beams, other damage mechanisms come into play (apparently for severe cases there is an actual popping sound perceived by the victim as the laser pulse creates a small shock wave inside the eye), and more of the victim's vision could be damaged.
Protective goggles aren't really an option, as they only protect against one wavelength. Attackers could then switch to a different type of laser (Ti:saph?). Combining goggles leads to virtually no light getting through.
References
Journal of Biomedical Optics 4(3), 337-344 (July 1999).
Big Sky Laser CFR-800 spec sheet [bigskylaser.com]
Re:Green with envy (Score:2, Informative)
Of course they never pointed out how accurately it was tracked. If it was just poping in and out of the cockpit on an intermittent basis, it could have been done by hand with a rifle scope or telescope to aid aiming.
However, power output wise, I must disagree about the truck mounted size. A class IIIa green laser pointer is visible hitting a target 2 miles away.
Sure you'd want something more powerful to be noticed clearly, a class IIIb device at least, but that at worst might make the laser itself the size of a pringles can instead of a laser pointer.
Now to accurately track it, the tracking gear might add a lot of size, but even that would be feasible to fit in a car trunk.
Charges against NJ man for lasering aircraft (Score:2, Informative)