Strange light phenomenon

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NorthlogicVFX
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Strange light phenomenon

Postby NorthlogicVFX » Mon Apr 04, 2016 1:53 pm

Anybody have any idea what that light is? It came from beyond the treeline and protruded and eventually vanished far off into the atmosphere. Shot few kilometers south of Sodankylä in Finland. My best guess is that it's a laser guide star for adaptive optics used in ground-based telescopes to correct atmoshperic distortions but I don't know if they have such an instrument in the Sodankylä observatory.

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Chris Peterson
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Re: Strange light phenomenon

Postby Chris Peterson » Mon Apr 04, 2016 3:03 pm

NorthlogicVFX wrote:Anybody have any idea what that light is? It came from beyond the treeline and protruded and eventually vanished far off into the atmosphere. Shot few kilometers south of Sodankylä in Finland. My best guess is that it's a laser guide star for adaptive optics used in ground-based telescopes to correct atmoshperic distortions but I don't know if they have such an instrument in the Sodankylä observatory.

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I'd guess it's just an ordinary green laser pointer. They're commonly used as telescope pointing aids by amateurs.
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neufer
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Re: Strange light phenomenon

Postby neufer » Mon Apr 04, 2016 5:12 pm

First polar stratospheric clouds visible in 532nm lidar around 25 km.
NorthlogicVFX wrote:
Anybody have any idea what that light is? It came from beyond the treeline and protruded and eventually vanished far off into the atmosphere. Shot few kilometers south of Sodankylä in Finland. My best guess is that it's a laser guide star for adaptive optics used in ground-based telescopes to correct atmoshperic distortions but I don't know if they have such an instrument in the Sodankylä observatory.
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Re: Strange light phenomenon

Postby bystander » Mon Apr 04, 2016 6:39 pm

The observatory at Sodankylä is a geophysical observatory and is unlikely to have telescopes requiring "guide stars".
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Chris Peterson
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Re: Strange light phenomenon

Postby Chris Peterson » Mon Apr 04, 2016 6:49 pm

bystander wrote:The observatory at Sodankylä is a geophysical observatory and is unlikely to have telescopes requiring "guide stars".

And artificial guide star systems don't normally use green lasers.
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neufer
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Re: Strange light phenomenon

Postby neufer » Mon Apr 04, 2016 6:49 pm

bystander wrote:
The observatory at Sodankylä is a geophysical observatory and is unlikely to have telescopes requiring "guide stars".

Well SOMEONE has "to correct atmoshperic [sic] distortions."
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Re: Strange light phenomenon

Postby neufer » Mon Apr 04, 2016 7:33 pm

http://www.usu.edu/alo/aboutlidar.htm wrote:

:arrow: The Atmospheric Lidar Observatory (ALO) gives rise to the green beam seen above the SER building at Utah State University (USU), Logan, Utah, on most clear nights

ALO Rayleigh Lidar
-----------------------------------
Laser (Nd:YAG) : 1065 nm
"frequency-doubled"
Wavelength : 532 nm
Energy per Pulse : 630 mJ
Repetition Rate : 30 Hz
Power : 19 W
Pulse Length : 7 ns (~2 meters)
Spectral Width (Seeded) : 150 MHz
Beam Divergence : 0.5 mrad

-----------------------------------------------
Potential eye hazard to about 150 miles(; ISS at 256 mi).

Temporary flashblindness hazard out to about 600 miles.

Distraction hazard to over 15,000 miles.
http://www.laserpointersafety.com/page5 ... agram.html wrote:
<<In the United States, lasers sold for pointing uses cannot exceed 5 mW. The diagram below shows the hazard distances for a 5 milliwatt “U.S. legal” green laser pointer with a 1 milliradian beam divergence:

    It is a potential eye hazard from the pointer to about 52 feet.

    It is a temporary flashblindness hazard from the pointer, out to about 260 feet.

    It is causes glare and is a disruption hazard from about 260 feet to about 1,200 feet.

    It is a distraction hazard from the pointer to over two miles (11,700 feet).
The laser’s light is not truly safe until it is indistinguishable from background lights on the ground. A pilot may notice a flashing dot of light, but it should not be enough to cause a distraction. (This does not mean that anyone should aim a 5 mW laser at a plane if it is over 2 miles away. For one thing, it is very difficult to gauge aircraft distances at night. Even more important, there simply is no reason to aim a laser at an aircraft except in an emergency situation such as a wilderness rescue.)>>
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Re: Strange light phenomenon

Postby NorthlogicVFX » Mon Apr 04, 2016 9:24 pm

Thanks for the replies, that clarified it for me

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Re: Strange light phenomenon

Postby NorthlogicVFX » Mon Apr 04, 2016 9:24 pm

neufer wrote:
bystander wrote:
The observatory at Sodankylä is a geophysical observatory and is unlikely to have telescopes requiring "guide stars".

Well SOMEONE has "to correct atmoshperic [sic] distortions."


Bit of sarcasm in there, was it incorrect information when I said that the laser guide stars are used for correcting atmospheric distortion?

EDIT: Fixed typo.

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neufer
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Re: Strange light phenomenon

Postby neufer » Tue Apr 05, 2016 12:47 am

NorthlogicVFX wrote:
neufer wrote:
bystander wrote:
The observatory at Sodankylä is a geophysical observatory
and is unlikely to have telescopes requiring "guide stars".

Well SOMEONE has "to correct atmoshperic [sic] distortions."

Bit of sarcasm in there,

    What, me sarcastic :?: (Never to be confused with going senile.)
NorthlogicVFX wrote:
...was it incorrect information when I said that the laser guide stars are used for correcting atmospheric distortion?

    No...but I liked it better the other way.
https://en.wikipedia.org/wiki/Laser_guide_star wrote:
<<Sufficiently bright stars are not available in all parts of the sky, which greatly limits the usefulness of natural guide star adaptive optics. Instead, one can create an artificial guide star by shining a laser into the atmosphere. This star can be positioned anywhere the telescope desires to point, opening up much greater amounts of the sky to adaptive optics. Because the laser beam is deflected by astronomical seeing on the way up, the returning laser light does not move around in the sky as astronomical sources do. In order to keep astronomical images steady, a natural star nearby in the sky must be monitored in order that the motion of the laser guide star can be subtracted using a tip–tilt mirror. However, this star can be much fainter than is required for natural guide star adaptive optics because it is used to measure only tip and tilt, and all higher-order distortions are measured with the laser guide star. This means that many more stars are suitable, and a correspondingly larger fraction of the sky is accessible.

There are two main types of laser guide star system, known as sodium and Rayleigh beacon guide stars.

Sodium beacons are created by using a laser specially tuned to 589.2 nanometers to energize a layer of sodium atoms that is naturally present in the mesosphere at an altitude of around 90 kilometers. The sodium atoms then re-emit the laser light, producing a glowing artificial star.

Rayleigh beacons rely on the scattering of light by the molecules in the lower atmosphere. In contrast to sodium beacons, Rayleigh beacons are a much simpler and less costly technology, but do not provide as good a wavefront reference, since the artificial beacon is generated much lower in the atmosphere. The lasers are often pulsed, with measurement of the atmosphere being time-gated (taking place several microseconds after the pulse has been launched, so that scattered light at ground level is ignored and only light that has traveled for several microseconds high up into the atmosphere and back is actually detected).>>
Art Neuendorffer

NorthlogicVFX
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Re: Strange light phenomenon

Postby NorthlogicVFX » Tue Apr 05, 2016 1:11 am

neufer wrote:
NorthlogicVFX wrote:
neufer wrote:Well SOMEONE has "to correct atmoshperic [sic] distortions."

Bit of sarcasm in there,

    What, me sarcastic :?: (Never to be confused with going senile.)
NorthlogicVFX wrote:
...was it incorrect information when I said that the laser guide stars are used for correcting atmospheric distortion?

    No...but I liked it better the other way.
https://en.wikipedia.org/wiki/Laser_guide_star wrote:
<<Sufficiently bright stars are not available in all parts of the sky, which greatly limits the usefulness of natural guide star adaptive optics. Instead, one can create an artificial guide star by shining a laser into the atmosphere. This star can be positioned anywhere the telescope desires to point, opening up much greater amounts of the sky to adaptive optics. Because the laser beam is deflected by astronomical seeing on the way up, the returning laser light does not move around in the sky as astronomical sources do. In order to keep astronomical images steady, a natural star nearby in the sky must be monitored in order that the motion of the laser guide star can be subtracted using a tip–tilt mirror. However, this star can be much fainter than is required for natural guide star adaptive optics because it is used to measure only tip and tilt, and all higher-order distortions are measured with the laser guide star. This means that many more stars are suitable, and a correspondingly larger fraction of the sky is accessible.

There are two main types of laser guide star system, known as sodium and Rayleigh beacon guide stars.

Sodium beacons are created by using a laser specially tuned to 589.2 nanometers to energize a layer of sodium atoms that is naturally present in the mesosphere at an altitude of around 90 kilometers. The sodium atoms then re-emit the laser light, producing a glowing artificial star.

Rayleigh beacons rely on the scattering of light by the molecules in the lower atmosphere. In contrast to sodium beacons, Rayleigh beacons are a much simpler and less costly technology, but do not provide as good a wavefront reference, since the artificial beacon is generated much lower in the atmosphere. The lasers are often pulsed, with measurement of the atmosphere being time-gated (taking place several microseconds after the pulse has been launched, so that scattered light at ground level is ignored and only light that has traveled for several microseconds high up into the atmosphere and back is actually detected).>>


Yeah, I have read up on this article as well.

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Fred the Cat
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Re: Strange light phenomenon

Postby Fred the Cat » Tue Apr 05, 2016 2:30 pm

May's S & T has a good review on Adaptive Optics.
Feynman's Felicity "Only ascertain as a cat box survivor"

Natalie Kaifler

Re: Strange light phenomenon

Postby Natalie Kaifler » Tue Sep 05, 2017 11:28 am

By chance I came across this post. Although it was last year, I want to clarify. The bright green beam is emitted by a so-called lidar, in this case a Rayleigh lidar used for sounding of the middle atmosphere. So it is a scientific instrument. It was built by the German Aerospace Center and was set up at Sodankylä from September 2015 to April 2016 as part of an atmospheric measurement campaign called GW-LCYCLE2 (http://www.pa.op.dlr.de/gwlcycle2/index.html). The goal was to study atmospheric gravity waves using a variety of ground-based and airborne instruments. The lidar measures density and temperature of the atmosphere up to almost 100 km at high resolution and is a state-of-the-art active atmospheric sounding instrument. It is housed in a small white container and is operated remotely at nighttime. I was at Sodankylä during installation and really enjoyed being there. What a beautiful place!
Many greetings from Munich, Natalie Kaifler


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