Why is the Sun visible with 3D Laser Scanning?

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AnthonyM
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Why is the Sun visible with 3D Laser Scanning?

Post by AnthonyM »

Hi,
I just wanted to know why the Sun appears in 3D laser scans I have taken when viewing the preview images from the scanner (i.e. using a FARO Focus 3D laser scanner). The images are in gray scale as they represent the intensity levels of the reflections from the laser. I notice that the sun itself is not captured but what appears to me to be the corona is somehow still recorded. Attached some of the laser scan preview images. Just really asking out of curiosity, any advice regarding what I'm looking at appreciated, thank you!
Image -  01.jpg
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Image -  02.jpg
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Re: Why is the Sun visible with 3D Laser Scanning?

Post by GreatAttractor »

Hi Anthony,
The Sun is the small black disc, correct? I suspect the rings are due to some internal reflection in your optics. If they were e.g. due to an actual halo in the atmosphere (matching your sensor's expected wavelength), I'd expect them to be circular without this truncation.


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Re: Why is the Sun visible with 3D Laser Scanning?

Post by Montana »

A very warm and sunny welcome Anthony :) these are quite incredible pictures.

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Re: Why is the Sun visible with 3D Laser Scanning?

Post by AnthonyM »

"The Sun is the small black disc, correct?" Yes that is right, it is actually the absence of the sun (i.e. black= no recorded data or no reflection of the laser light bouncing back to the scanner from the surrounding surfaces and grey scale for the reflection value of everything in between). Sounds plausible regarding internal reflections within the scanner as you mentioned the visible rings are truncated/cut off on either end.

Its still odd to me that the sun itself is not recorded at all yet some artifacts in terms of the rings etc are still there in the 3D scan. So the scanner is picking up some solar wavelengths but not the sun itself. Also strange that the scanner is recording anything at all in terms of solar radiation since even if the solar wavelengths recorded match those of the laser, the 3D laser scanner is meant to record the time of flight of the laser light generated internally and bouncing back to give an exact distance to surfaces and hence their geometry, repeated millions of times during the scanning process to generate a 3D pointcloud of data - there is no time of flight/distance data associated with the sun yet there it is :)
Close up image with brightness/contrast enhanced
Close up image with brightness/contrast enhanced
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Re: Why is the Sun visible with 3D Laser Scanning?

Post by Montana »

Do you know what wavelength of light the laser is (nm)?

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Re: Why is the Sun visible with 3D Laser Scanning?

Post by AnthonyM »

Hi Alexandra,
The tech sheet for the scanner mentions a wavelength of 1550nm, thanks.


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Re: Why is the Sun visible with 3D Laser Scanning?

Post by Montana »

Thanks Anthony,

I was wondering whether it was picking up any known absorption lines and thus faint emission in that region. The Sun is black hinting at an absorption line, otherwise I would have thought it would have emitted plenty of light at 1550nm. Here is a link showing the main lines which solar observers look at
https://solarnutcase.livejournal.com/9556.html

Your scanner is looking for light at 1550nm, the question is, is that what it emits or what it is looking for when it is rebounded? would that be slightly red shifted when rebounded? I have no idea.

But there is one line at 1565nm Fe I, however that is used for the photosphere and magnetic lines. Nothing in the corona. You are about 15nm further into the blue which equates to 150 angstroms which is quite wide. Usually for these spectral lines you need a width of 2-4 A to see anything (within the width of the band).

It is quite a remote thought but possible and a nice idea, but I am absolutely no expert. Very interesting though. The most probable cause is as said before some reflections.

Alexandra
PS I will copy this topic and add it to the spectroscopy part of the forum. There are some geeks in there who may know more and may spot this post.


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