Modified the issue with the calibration coefficient indices for FY-3 satellite data reader

[sgxl]

"There were issues with etc/readers/mersi2_l1b.yaml and etc/readers/mersi3_l1b.yaml. Minor code changes have been made:

According to the MERSI data document, the 'calibration_index' in Satpy was incorrect. The VIS_Cal_Coeff dataset includes calibration coefficients for both 250m (Data/EV_250_Aggr.1KM_RefSB) and 1km (Data/EV_1KM_RefSB) bands. The calibration coefficients are ordered by band sequence. Previously, the calibration indices for Data/EV_1KM_RefSB started from 0, which is incorrect; they should start after the last index of the 250m visible band.

Xuanhan Lai

[djhoese]

Thanks!

I think this makes sense to me so I'm OK with the index changes, but why the removal of the "radiance" calibration?

Also, do you have an example of what one of the visible channels looked like before and after these changes? Is there an obvious improvement?

[djhoese]

Are these indexes still valid/correct when the other coefficient list is used:

satpy/satpy/readers/mersi_l1b.py

Line 110 in e0eb086

coeffs = self["/attr/VIR_Cal_Coeff"]

"/attr/VIR_Cal_Coeff"

[sgxl]

Thank you for pointing out the mistakes in my code regarding the incorrect removal of 'radiance.' These issues may have been due to using older versions of the code. I have fixed them.

I have plotted the comparison charts before and after the "calibration_index" modifications:

[sgxl]

I have already checked the fy3a_mersi1_l1b.yaml, fy3b_mersi1_l1b.yaml, and fy3a_mersi1_l1b.yaml files before the pull request, and I did not find any obvious errors with the calibration index.

[sgxl]

https://essd.copernicus.org/articles/12/1123/2020/essd-12-1123-2020-f04-web.png

Thank you for pointing out the mistakes in my code regarding the incorrect removal of 'radiance.' These issues may have been due to using older versions of the code. I have fixed them.

I have plotted the comparison charts before and after the "calibration_index" modifications:

And for ocean water spectra, there typically should not be an absorption dip at 443 nm. The common shape of water body spectra can be referred to: https://essd.copernicus.org/articles/12/1123/2020/essd-12-1123-2020-f04-web.png

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.08%. Comparing base (d6b8d01) to head (927769f).
Report is 308 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2959      +/-   ##
==========================================
- Coverage   96.09%   96.08%   -0.02%     
==========================================
  Files         377      377              
  Lines       55125    55125              
==========================================
- Hits        52975    52967       -8     
- Misses       2150     2158       +8     

Flag	Coverage Δ
behaviourtests	3.94% <ø> (ø)
unittests	96.18% <ø> (-0.02%)	⬇️

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[coveralls]

Pull Request Test Coverage Report for Build 11622341982

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 8 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.02%) to 96.191%

---

Files with Coverage Reduction	New Missed Lines	%
satpy/tests/utils.py	2	93.16%
satpy/tests/reader_tests/gms/test_gms5_vissr_l1b.py	3	98.67%
satpy/tests/reader_tests/gms/test_gms5_vissr_navigation.py	3	97.18%

Totals
Change from base Build 11519685240:	-0.02%
Covered Lines:	53211
Relevant Lines:	55318

---

💛 - Coveralls

[mraspaud]

@sgxl thanks for your work! We are just waiting for @simonrp84 to review this PR as he has been working with the FY3 data and readers...

[simonrp84]

Reminder to myself to look at this early next week!

[mraspaud]

Approving this as I got the green light from @simonrp84 !