Geocolor night

[Roman Zamiesal]

Hi all,

Where can I find the geocolor night composition in pytroll, I need a code on how to create a geocolor night,

Thanks Roman.

[Martin Raspaud]

Hi Roman,

Why don’t you start by showing us what you tried so far, and we can help you from there?

Best regards

Martin

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[Roman Zamiesal]

Hi Martin,

I create geocolor night in C#, I use the settings from atot-JTECH-D-22-0107.pdf, the problem is in the high transparency between the high clouds and the night lights from the background, I use the formula High_Clouds * 1.0 + (1.0 - High_Clouds) * ((Low_clouds) + (1.0 - Low_clouds) * (Night_light_Background)), I don't know where the problem is, I attach two different images org.jpg and me.jpg, the view is clear.

Roman.

št 9. 1. 2025 o 9:13 Martin Raspaud <martin....@smhi.se> napísal(a):

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[Martin Raspaud]

Hi Roman,

I’m not the best in the community to answer geocolor questions as I’ve
not been involved in the implementation myself, but maybe this is
relevant:
https://github.com/pytroll/satpy/blob/7e31b159072a04e748c8344fbed884dc7354bcae/satpy/composites/__init__.py#L1085

Now, just a word of caution before you start porting satpy algorithms
to your program: satpy is GPLv3, which means that code ported from it is
derivative work and should comply to the license.

I’ll try to ping relevant people to the discussion.

Best regards,
Martin

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[Johan Strandgren]

Hi Roman,

from your example it looks like the high cloud layer has too high transparency. The transparency is determined by the brightness temperature and while the limit for full transparency is constant at 300 K, the limit for full opacity depends on the latitude. In short:

latitude < 30 degrees: Full opacity at BT < 210 K

latitude > 60 degrees: Full opacity at BT < 230 K

latitude between 30 and 60 degrees: limit for full opacity derived via linear interpolation between 210 and 230 K.

Do you have something like this implemented?

You can also have a look at this paper, which is the GeoColor paper on which the satpy implementation is largely based: https://journals.ametsoc.org/view/journals/atot/37/3/JTECH-D-19-0134.1.xml

Cheers,
Johan

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Tel: +49 1523 611 3407

[Roman Zamiesal]

I don't need to copy the pytroll code. Yes Johan, I probably found a problem in my code, the transparent factor is missing. Thanks for the help.

Dňa pi 10. 1. 2025, 9:59 Johan Strandgren <johan.st...@gmail.com> napísal(a):

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