Dear Ted
Thanks for your proposals. I have a few comments and questions.
* What is the difference between TOA reflectance and planetary albedo (the
latter is an existing standard name)?
* solar_zenith_angle is an existing std name, so that would be preferable
to sun_angle.
* "normalized" is a vague word. It means different things in various contexts.
Although I expect this is the usual technical term, for a CF standard name
it would be good to say more explicitly what it means here e.g.
multiplied_by_cosine_solar_zenith_angle
!
Cheers
Jonathan
----- Forwarded message from Ted Kennelly <ekennell at aer.com> -----
> Date: Tue, 7 May 2013 13:47:33 -0400
> From: Ted Kennelly <ekennell at aer.com>
> User-Agent: Thunderbird 2.0.0.24 (Macintosh/20100228)
> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Subject: [CF-metadata] New reflectance standard names
>
> 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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----- End forwarded message -----
Received on Tue May 07 2013 - 13:44:14 BST
