Fix radiance units of geostationary satellites

[sfinkens]

Fix radiance units of geostationary satellites and add references where missing. Now the value ranges of SEVIRI, ABI and AHI radiances are consistent (taking into account that toa_radiance_per_unit_wavenumber = wavelength^2 * toa_radiance_per_unit_wavelength).

• Closes Inconsistent units of geostationary radiances #414
• Passes git diff origin/master -- "*py" | flake8 --diff

[djhoese]

Why is this needed? You've also changed the units for ABI that are specified in the file as:

Rad:units = "W m-2 sr-1 um-1" ;

Are your units equivalent?

[sfinkens]

For channels 1-6 the units are indeed W m-2 um-1 sr-1. But for channels 7-16 it is mW m-2 sr-1 (cm-1)-1, also in the files. See the GOES-R Data Book, page 3-2.

[djhoese]

You got me there. Thanks for the clarification. So AHI doesn't follow the same pattern?

[djhoese]

If the test failures don't seem like your fault then don't worry about it. This is a bug with the conda-forge package of imageio that I've been debugging for the last day. A fix should be coming out in the next day or so and we can rerun these tests.

[sfinkens]

Rows 8 & 9 in the table on page 14 of the AHI User Guide indicate that they use the same units for all channels. ABI seems to be the only instrument with varying radiance units.

Regarding the test failure: Ok, let's wait for the fix.

[coveralls]

Coverage decreased (-0.02%) to 73.911% when pulling 033b719 on sfinkens:fix-geos-radiance-units into 5dd28ea on pytroll:master.

[djhoese]

Too bad the coverage went down just because documentation was added. Thanks for looking in to this.