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 <[email protected]> ----- > Date: Tue, 7 May 2013 13:47:33 -0400 > From: Ted Kennelly <[email protected]> > User-Agent: Thunderbird 2.0.0.24 (Macintosh/20100228) > To: "[email protected]" <[email protected]> > 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. > > > > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
