I would like to propose the following standard names:
“toa_lambertian_equivalent_reflectance”
“Reflectance is the ratio of the energy of the reflected to the incident
radiation. A coordinate variable can be used to specify the radiation
wavelength or frequency. ‘toa’ means top of atmosphere.
‘Lambertian_equivalent’ means the quantity is evaluated for a diffusely
reflecting surface.”
units = 1
“toa_lambertian_equivalent_reflectance_normalized_by_sun_angle”
“Reflectance is the ratio of the energy of the reflected to the incident
radiation. A coordinate variable can be used to specify the radiation
wavelength or frequency. ‘toa’ means top of atmosphere.
‘Lambertian_equivalent’ means the quantity is evaluated for a diffusely
reflecting surface. “normalized_by_sun_angle” means that the quantity
has been multiplied by the cosine of the solar zenith angle of the
incident solar radiation.”
units = 1
Rationale: these are key product of the GOES-R program that are used for
downstream L2 processing and as the end-product in the imagery product.
On GOES-R, the imagery product is referred to as the "reflectance
factor". It is equal to the "reflectence" times the cosine of the solar
zenith angle such that the signal drops off in the terminator region as
does the observed L1b radiance product. The "reflectance" and
"reflectance factor" are computed assuming diffuse reflection off a
Lambertian surface and represent the signal measured at the top of the
atmosphere. The existing CF standard name
"toa_bidirectional_reflectance" has not been adopted because it 1)
implies a directional dependence of the radiation and 2) does not
address the need for the normalized quantity. The term "lambertian
equivalent reflectance" or sometimes just "equivalent reflectance" has
been used on certain programs to specify assumptions made in the
calculation. In particular the assumption of a Lambertian surface
results in a factor of PI in the formula: rho = PI * L/ mu / E, where L
is the observed radiance, E is the solar irradiance, and mu is the
cosine of the solar zenith angle. This is
critical information for the users of the product.
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