Fix VII (METimage) reader angles names

[ameraner]

This PR fixes the names of satellite and solar angles in the yaml file of the VII/METimage reader, so that they adhere to the convention and are correctly used in predefined modifiers, such as the sunz_corrected defined in generic.yaml. As discussed in https://pytroll.slack.com/archives/C0LNH7LMB/p1765897278746739 .

Before this PR, the sunz_correction was not using the in-file angles as they could not be found due to the different name, causing issues when correcting Scenes with granules that were far apart in time; see the bright overcorrection over Europe, solved by this PR:
before

after

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.33%. Comparing base (2554db5) to head (c83da7b).
⚠️ Report is 18 commits behind head on main.

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- Coverage   96.34%   96.33%   -0.02%     
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  Files         463      463              
  Lines       58916    58916              
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- Misses       2156     2162       +6     

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[pnuu]

LGTM

Just wondering whether "observation" and "satellite" zenith angles are the same thing? It could be argued that observation zenith angle is the angle in which the satellite makes the measurement, while satellite zenith angle is the angle the satellite is seen from the observed location.

[ameraner]

Yeah, I think "sensor", "viewing", "observation" and "satellite" _zenith are used interchangeably in the community - even in satpy each one of these is used. I went for "satellite" since that's what the default modifiers use, e.g.

satpy/satpy/etc/composites/visir.yaml

Lines 52 to 63 in 579e797

	rayleigh_corrected:
	modifier: !!python/name:satpy.modifiers.PSPRayleighReflectance
	atmosphere: us-standard
	aerosol_type: rayleigh_only
	prerequisites:
	- wavelength: 0.67
	modifiers: [sunz_corrected]
	optional_prerequisites:
	- satellite_azimuth_angle
	- satellite_zenith_angle
	- solar_azimuth_angle
	- solar_zenith_angle

I checked and at the center of the swath the value is 0 (not 90), so that's as expected I'd say.

[ameraner]

To confirm even more that the file variable indeed contains the commonly used viewing/satellite angle (the angle under which the satellite is seen from the ground): the METimage scanner goes up to +- 54.21°, while the "observation angle" data in the file goes up to e.g. 66.8° in my test granule. So I think we're good :)

[pnuu]

Thanks for confirming!

CI build for Windows is failing on unrelated E rasterio._err.CPLE_AppDefinedError: Cannot open TIFF image error. I'll try restarting the tests, even if this isn't the typical Zenodo or Conda hickup.