When is reflectance actually reflectance?

Problem

WARNING: I'm not a scientist.

This is related to #52, specifically the standard_name used for visible channel data returned by SatPy. We return visible channel data in the "reflectance" calibration with the standard_name of toa_bidirectional_reflectance. By CF definition this term should only be used for reflectance data that includes the normalization for the solar zenith angle (SZA). This normalization (as some may know) is applied by dividing by the cos(sza). While talking with @kathys, she mentioned that she has always referred to the data without this SZA adjustment as "normalized radiances" (normalized for the theoretical maximum energy entering the atmosphere from the sun, not for the angle of the sun).

The CF definition for toa_bidirectional_reflectance:

"Bidirectional_reflectance" depends on the angles of incident and measured radiation. Reflectance is the ratio of the energy of the reflected to the incident radiation. A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation. "toa" means top of atmosphere. toa_bidirectional_reflectance includes a factor to account for the cosine of the solar zenith angle but does not include any integration over solid angle.

So, I'm wondering if we should be listing the pre-sunz corrected reflectances as having a different standard_name. Thoughts?

Special Notes

• VIIRS SDRs already have the sunz correction done to them so toa_bidirectional_reflectance is actually correct for that reader
• Both pre-sza and post-sza adjustment data are unitless, so this can't be used to know which is which.
• I can't find a CF standard name that seems to apply to the pre-SZA adjustment reflectance data.