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Guru

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First 'Images' of Thunder: Sound Waves Captured Visually

05/07/2015 7:57 AM

May 5, 2015
Source:
Southwest Research Institute
Summary:
For the first time, scientists have imaged thunder, visually capturing the sound waves created by artificially triggered lightning. By studying the acoustic power radiated from different portions of the lightning channel, researchers can learn more about the origins of thunder as well as the energetic processes associated with lightning

http://www.sciencedaily.com/releases/2015/05/150505121328.htm

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Guru

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#1

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/07/2015 12:04 PM

Another prime example of the capabilities of modern signal processing. I wonder what the acoustic signature of an explosive charge like primacord would look like?

Thanks.

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Guru

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#2

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/07/2015 7:59 PM
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Guru

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#3

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/07/2015 11:21 PM

? So?

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Guru

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#4

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/08/2015 10:57 AM

Sorry for my ignorance, but it looks like a high school science project to me ...

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Guru

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#5

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/08/2015 12:13 PM

I like sciencedaily.com and their write ups are usually reasonably free of glaring errors. So, I was a bit surprised to read a comment that seemed to suggest the author doesn't really understand what they are reporting on.

I wanted to make sure I wasn't the one with a failure to understand, so I went to the actual paper. Much to my surprise, it wasn't sciencedaily.com that made the comment. The comment was published with the actual paper.

".... The apparent tilt of the lightning bolt in the left photo is also seen in the acoustic image...."

.

The x axis of the acoustic image is time. Assuming the accompanying photograph was taken from the same direction as the acoustic image, the apparent tilt of the lighting bolt has nothing to do with the slope seen on the acoustic image.

The lighting bolt might also, non apparently may have been tilted with the upper portion more toward the place the acoustic image and photograph were taken, but again that would be non apparent.

.

Am I reading this wrong, or did they make a misstatement on the subject of their field of expertise publishing an academic paper?

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Guru

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#6
In reply to #5

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/08/2015 5:08 PM

Am I reading this wrong, or did they make a misstatement on the subject of their field of expertise publishing an academic paper?
You are correct. The misstatement led me to believe it was a 2D beam intensity plot at first, until I noticed the x-axis was time. They supposedly compensated for range so the orientation of the lightening discharge should have no effect on the time plot. I don't know why it was tilted, maybe the range compensation was not done correctly.

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Guru

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#7
In reply to #6

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/08/2015 5:18 PM

Thanks for the confirmation. I was really second guessing myself when it became apparent the error was so close to the research.

.

The sound at greater height could be traveling ahead of the lower sound in the bolt was tilted at an angle with upper portions closer than the lower...becoming somewhat overhead. If the sound measurements had come from a location substantially to the left of where the photograph came from for the strike in the first picture, it might have that effect..

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Guru

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#8
In reply to #7

Re: First 'Images' of Thunder: Sound Waves Captured Visually

05/08/2015 6:30 PM

They state that a correction was made for the delay due to the speed of sound. This delay would be both due to the geometry (distance to the wire) and wind speed. It could be that there was a momentary gust of wind that distorted the sound speed at the time the strike occurred that wasn't figured in.

Although it was not described, I would assume that they had 2 or more cameras set up to know the exact path of the rocket and wire.

I thought it was interesting that the experimenter was surprised about the resolution at different sound frequencies. The relationship between wavelength, array size, and resolution is pretty basic beamforming knowledge (but perhaps he was being conversational for the interviewer).

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