Re:Start of Lightning Bolt Caught on Camera
by rmcpherson on Friday October 23, 2015 @10:25AM
(#10438733)
Great video, the nature article is much more informative than the one linked.
From the nature article, it seems this was the first video of natural bidirectional lightning, not triggered by rockets or aircraft: "In contrast to studies of rocket-triggered lightning and lightning initiated by aircraft, which found delays of 3–6 ms between the onset of negative and positive leader branches, this natural event exhibited a delay of less than 90 μs (i.e. one video image)."
This was a negative polarity lightning strike. the most common type. Less than 5% of lightning is positive polarity but they can carry ten times the charge and exceed a billion volts of potential.
Re:Start of Lightning Bolt Caught on Camera
by omribahumi on Friday October 23, 2015 @11:13AM
(#10439073)
Are the positive ones the "bigger" ones?
EDIT: From the linked Wikipedia entry: "Because of the much greater distance to ground, the positively charged region can develop considerably larger levels of charge and voltages than the negative charge regions in the lower part of the cloud."
Re:Start of Lightning Bolt Caught on Camera
by jrowley on Friday October 23, 2015 @02:43PM
(#10440509)
The only issue with gifv is that if you open one on iOS it will pause whatever music you're listening to at the time. Kind of a bummer and something that will hopefully eventually get fixed.
Re:Start of Lightning Bolt Caught on Camera
by dang on Friday October 23, 2015 @10:28AM
(#10438753)
That's obviously more substantive, and HN prefers original sources, but unfortunately it doesn't include a link to the video, so I guess we'll leave the URL as is.
Re:Start of Lightning Bolt Caught on Camera
by elfchief on Friday October 23, 2015 @12:42PM
(#10439710)
The cameras doing a billion+ frames/sec do not really function the way traditional cameras do -- i.e. you could never use one to take a picture of lightning (which is a pity). They work by firing off billions of extremely short bursts of laser light, and capturing images at progressively longer offsets from the release of a pulse. That strobing light is an integral part of how those cameras work, so they can only be used in situations where you can control the illumination of the object.
(Which does not make that technology, mind you, any less cool. But it's different enough from traditional photography that I thought it was worth mentioning.)
Re:Start of Lightning Bolt Caught on Camera
by webXL on Friday October 23, 2015 @11:20AM
(#10439128)
But that would just be for one recording device. If you could use multiple devices, perhaps with small POV differences that could be corrected, I would expect no limit in that "lossy" case.
Re:Start of Lightning Bolt Caught on Camera
by javajosh on Friday October 23, 2015 @11:47AM
(#10439338)
But if you surrounded an event with a sphere of sensors, there is still an upper limit. The number of sensors is a function of sphere radius, and whether they are limited to the surface of the sphere (which is reasonable since tightly packed sensors will, in general, get in the way of other sensors).
A sphere 1km across has a surface are of 4pi1km^2 which is roughly 10^7m^2. If you had 1cm^2 sensors then you get 10^4 sensors per m^2, which means you get 10^11 sensors total. At 11k fps (10^4) that's a total of 10^15 fps.
Note that Planck time is 10^-44 so such an arrangement probably wouldn't help for detecting quantum gravity because you'd run out of matter in the universe before you could construct the sensors.
Re:Start of Lightning Bolt Caught on Camera
by InclinedPlane on Friday October 23, 2015 @09:08PM
(#10442020)
Ultimately, sure, you run out of photons.
Let's start off with a baseline image resolution of 1 megapixel.
1 Joule is about 6E18 visible light photons, give or take. So that's then 6E12 photons per pixel.
Full sunlight on Earth has an intensity of around 1400 Watts (Joules/second) per square meter, or 0.14 Watts per square cm.
So achieving a frame rate in the trillions of fps would likely run into some limits relative to the size of your optics, the intensity of light coming from the scene, or the bulk quantum efficiency of the sensor.
And, of course, if you try to achieve quintillions of fps then you start dumping in nearly an entire Watt in photons into every single pixel on your sensor, which rapidly becomes a very big problem re: everything melting.
Additionally, modern electronics has trouble operating above the low GHz range, beyond that you'd need to move to superconductors or some such to keep up with the data.
Re:Start of Lightning Bolt Caught on Camera
by leni536 on Friday October 23, 2015 @01:24PM
(#10439976)
The number of captured photons is a good hard limit. dalke's answer for ultrafast photography is kind of "cheating" in the sense that they record the same event periodically so they can gather enough light. That technique can't record single unique events that fast AFAIK.
Re:Start of Lightning Bolt Caught on Camera
by dalke on Friday October 23, 2015 @04:39PM
(#10441172)
No, it's not "cheating."
The title of my link says 'single-shot'. The underlying Nature article at http://www.nature.com/nature/journal/v516/n7529/full/nature1... says "Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10^11 frames per second"
Re:Start of Lightning Bolt Caught on Camera
by skizm on Friday October 23, 2015 @11:53AM
(#10439382)
Not that it isn't awesome how fast cameras are, just keep in mind, the clip is 25ms. So at 11,000 fps, that would be 275 images (11 frames per ms). Not sure if we actually have a camera that can take 11,000 images in 1 second. (I guess that depends on the resolution)
Re:Start of Lightning Bolt Caught on Camera
by justifier on Friday October 23, 2015 @11:46AM
(#10439326)
lightning is enigmatic
and the internet facing community surrounding its research seems divisive
can anyone speak to the sort of research currently being done on the study of lightning and its initiation?
are there efforts to recreate assumed initial conditions?
thoughts on the source of the huge amounts of directed energy? does the strike harvest from the vast collection of charged particles within the cloud or is it created by electrostatic interaction of individual ions, similar to http://www.nature.com/nchem/journal/v7/n3/full/nchem.2161.ht...?
Re:Start of Lightning Bolt Caught on Camera
by vegabook on Friday October 23, 2015 @12:57PM
(#10439809)
a) overloaded site
b) very nice, but is this "Hacker" News? More like Discovery Channel. How is this interesting from a tech point of view? High FPS cameras. Got it. Got it long ago.
From the nature article, it seems this was the first video of natural bidirectional lightning, not triggered by rockets or aircraft: "In contrast to studies of rocket-triggered lightning and lightning initiated by aircraft, which found delays of 3–6 ms between the onset of negative and positive leader branches, this natural event exhibited a delay of less than 90 μs (i.e. one video image)."
This was a negative polarity lightning strike. the most common type. Less than 5% of lightning is positive polarity but they can carry ten times the charge and exceed a billion volts of potential.
When you read about people surviving lightning strikes it's almost certainly a negative polarity strike. https://en.wikipedia.org/wiki/Lightning#Positive_and_negativ...
EDIT: From the linked Wikipedia entry: "Because of the much greater distance to ground, the positively charged region can develop considerably larger levels of charge and voltages than the negative charge regions in the lower part of the cloud."
Also, having Cloud to Butt extension installed made reading that Wikipedia quote quite interesting...
Great Scott!
[0] https://i.imgur.com/W1X1qFI.jpg
https://i.imgur.com/W1X1qFI.jpg
https://i.imgur.com/W1X1qFI.gif
https://i.imgur.com/W1X1qFI.png
link to the same GIF. :)
Better if you request with .gifv extension, then it's a much smaller (than a gif) html5 video)
W1X1qFI which happens to be the url/filename and is auto-generated it ignores the extension
instead of throwing a 404.
That got me thinking, is there any theoretical limit to the number of frames that can be captured in one second?
(Which does not make that technology, mind you, any less cool. But it's different enough from traditional photography that I thought it was worth mentioning.)
A sphere 1km across has a surface are of 4pi1km^2 which is roughly 10^7m^2. If you had 1cm^2 sensors then you get 10^4 sensors per m^2, which means you get 10^11 sensors total. At 11k fps (10^4) that's a total of 10^15 fps.
Note that Planck time is 10^-44 so such an arrangement probably wouldn't help for detecting quantum gravity because you'd run out of matter in the universe before you could construct the sensors.
Let's start off with a baseline image resolution of 1 megapixel.
1 Joule is about 6E18 visible light photons, give or take. So that's then 6E12 photons per pixel.
Full sunlight on Earth has an intensity of around 1400 Watts (Joules/second) per square meter, or 0.14 Watts per square cm.
So achieving a frame rate in the trillions of fps would likely run into some limits relative to the size of your optics, the intensity of light coming from the scene, or the bulk quantum efficiency of the sensor.
And, of course, if you try to achieve quintillions of fps then you start dumping in nearly an entire Watt in photons into every single pixel on your sensor, which rapidly becomes a very big problem re: everything melting.
Additionally, modern electronics has trouble operating above the low GHz range, beyond that you'd need to move to superconductors or some such to keep up with the data.
The title of my link says 'single-shot'. The underlying Nature article at http://www.nature.com/nature/journal/v516/n7529/full/nature1... says "Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10^11 frames per second"
These can do 25k fps at 1280x800 pixels (and 1 million fps at 128x32 pixels): http://www.visionresearch.com/Products/High-Speed-Cameras/UH...
and the internet facing community surrounding its research seems divisive
can anyone speak to the sort of research currently being done on the study of lightning and its initiation?
are there efforts to recreate assumed initial conditions?
thoughts on the source of the huge amounts of directed energy? does the strike harvest from the vast collection of charged particles within the cloud or is it created by electrostatic interaction of individual ions, similar to http://www.nature.com/nchem/journal/v7/n3/full/nchem.2161.ht...?
b) very nice, but is this "Hacker" News? More like Discovery Channel. How is this interesting from a tech point of view? High FPS cameras. Got it. Got it long ago.