Hydrogen alpha spectral shift video and gif

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thesmiths
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Hydrogen alpha spectral shift video and gif

Post by thesmiths »

As I mentioned in our previous post viewtopic.php?t=36970, there's a lot of data in the SHG video files. An example of what can be extracted is what we call the "pixel shift" feature in our software. This moves the reconstruction line plus and/or minus from the centre of the spectral line (assumed to be the minimum or darkest line) when reconstructing the image. That means creating narrowband images shifted by small wavelength increments, the smallest increment being 1 pixel in the video file. What this pixel shift corresponds to depends upon the dispersion (in angstroms per pixel, or I prefer using picometers per pixel). Using Ken's SimSpec SHG spreadsheet, I calculate that each pixel shift corresponds to a wavelength shift of 7.9 picometres.

In an earlier post viewtopic.php?t=36895, we showed the wavelength shifted images as a mosaic. This time, we tried showing them as a video. The video below was done with the frames pixel shifted by -8, -7, ... 0, 0, .. 7, 8. So 19 frames in total, from a wavelength of +0.63 angstrom (red shifted) to -0.63 angstroms (blue shifted). The theoretical spectral resolution is around 0.2 angstroms.



As the video is made up of 19 frames with 2 seconds per frame, it lasts 38 seconds, which I realise now is a bit long. It actually looks betters if you speed it up to 2X.

It's not so obvious in the video, but there are interesting differences if you looks at the -x vs x shifted images. I made a GIF from the -5 and 5 pixel shifted images which seemed to show the most dramatic differences.

H-alpha SHG images, shifted -5 and 5 pixels
H-alpha SHG images, shifted -5 and 5 pixels
103655_shift=-5,5.gif (338.16 KiB) Viewed 373 times

I think a lot of the changes are because of doppler effects. Around most of the active regions, there are differences that are likely due to material travelling at different velocities (up or down from the surface). There is also an overall East/West effect, presumably due to the solar rotation. The solar rotation doppler shift gives some scale to the velocity shifts we are talking about.

The area at the bottom left seemed to have a lot going on so I made a 100% crop of just this area and used the -4 and +4 pixel shifted images. In this case, I also used imppg and Photoshop (but treated both frames exactly the same):

Closeup of -4 and +4 pixel shifted H-alpha SHG images
Closeup of -4 and +4 pixel shifted H-alpha SHG images
103655-shift+4,-4.gif (1.66 MiB) Viewed 372 times

With enough imagination, you can see what might be material rolling up and over. It's worth mentioning that these two images were taken from the same video data so were acquired simultaneously (even though it looks similar to a time lapse). They are two images acquired at the same time, separated by 0.63 angstroms in wavelength. It's also worth noting that the images are noisier than the stacked images posted previously (taken from video data at many different times) but in some ways they are a little sharper.


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Re: Hydrogen alpha spectral shift video and gif

Post by Montana »

This is absolutely fabulous, there is so much information in these images :bow :bow :bow the solar rotation doppler effect is very marked, I noticed this immediately :hamster:

Alexandra


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