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How does Atmospheric Correction work?

  1. May 13, 2015 #1
    I have been reading about it a lot, but I still cannot grasp the concept and procedure of Atmospheric Correction. If, for example, a have a raw image from a satellite, how does Atmospheric Correction do its processes, and what would be the expected resulting image?
     
  2. jcsd
  3. May 13, 2015 #2

    CWatters

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    Not my field but...

    Data received by a camera can be affected by anything that is between the object being photographed and the camera. So photos of divers taken underwater make their faces look a funny colour depending on what is in the water. Likewise data collected by a satellite is affected by what's in the atmosphere. For example if you want to know the spectra of a rock to work out it's composition that might be affected by the spectra of the light source and what's in the atmosphere between the rock and the camera/sensor.

    NASA explains..

    http://mars.nasa.gov/mer/mission/spacecraft_instru_calibr.html

    I imagine there are a large number of different atmospheric corrections that can be applied depending on what you are trying to achieve.
     
  4. May 13, 2015 #3

    Andy Resnick

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    Are you referring to the process of correcting the effects of clear air turbulence on imaging?

    https://www.crcpress.com/product/isbn/9780849337871
     
  5. May 13, 2015 #4
    @CWatters - Thank you for the analogy. So, if I were to do a program regarding this, should it be pixel by pixel, as long as I have a reference pixel or color?

    @Andy Resnick - Yes, it is correcting the effects of the atmosphere on the image. Not just the turbulence, though. Here is an article I just read: http://www.researchgate.net/profile/Andreas_Mueller15/publication/225018984_An_automatic_atmospheric_correction_algorithm_for_visibleNIR_imagery/links/00b7d5267e226938b3000000.pdf [Broken]
     
    Last edited by a moderator: May 7, 2017
  6. May 13, 2015 #5
    If I remember correctly, one easy way of correcting for turbulence is by using a reference point that you know what it looks like and where it should be on the sky. The deformations on that reference point are then used for deriving a back-transformation for the rest of the image.
     
  7. May 14, 2015 #6

    CWatters

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    Perhaps google the dark pixel technique. From what I can see technique looks for dark pixels and assumes they should be black. If they aren't they assume all pixels are too bright by a similar amount....although I suspect it's far more complicated than that.

    http://www.cesbio.ups-tlse.fr/multitemp/?tag=atmospheric-correction

     
    Last edited by a moderator: May 7, 2017
  8. May 14, 2015 #7

    Andy Resnick

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    It depends on what the OP means by 'atmospheric correction'. Rumborak is correct, often a 'guide star' is used with a Shack-Hartmann wavefront sensor to correct for turbulence induced aberrations, and AFAIK, some sort of reflectance standard is often used for photogrammetric correction of imagery as well.
     
  9. May 14, 2015 #8

    Drakkith

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    Image processing and correction is extremely complicated. My book on image processing for amateur astronomers is around 600 pages long!
     
  10. May 14, 2015 #9
    @rumborak , @CWatters, @Andy Resnick - Thank you! At least, I am confident that I need some sort of "reference" for the correction.

    @Drakkith - What book is this? I wonder if it is helpful for Earth observations from space or from a satellite.
     
  11. May 14, 2015 #10

    Drakkith

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    It's bundled with an image processing software, link here: http://www.willbell.com/aip/Index.htm [Broken]
    It's focused on observing the skies, but you may be able to get a better understanding of image processing techniques using it.
     
    Last edited by a moderator: May 7, 2017
  12. May 14, 2015 #11
  13. May 14, 2015 #12

    Drakkith

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    No problem.

    By the way, there's no need to tag people in your post to reply to them. You can use the 'Reply' feature to quote someone's entire post, use the 'Quote' feature to add multiple posts to the quote que (just click Insert Quotes at the bottom left of the reply box to put the posts in the quote que into the reply box), or highlight the part of the post you want to reply to and click 'Reply' or 'Quote'. In addition, replying to a post automatically notifies anyone who has responded in thread that there's a new post.
     
  14. May 14, 2015 #13
    Thanks for the advice. I didn't know that it's actually "tagging" people. I honestly thought that it is just a way to clear up to whom is the reply is for. :wink:
     
  15. May 14, 2015 #14

    Drakkith

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    Nope, it tags them and they get a notification that they've been tagged in a post. Just like this: @ecastro
     
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