Dear John N, John G, David and Jonathan,
It is clear from the discussion so far that this is a surface quantity, so in fact we should include that in the name:
surface_normalized_radar_backscatter_coefficient
canonical units: 1
I agree that scalar coordinate variables would be needed for the radiation_wavelength and angle_of_incidence. A similar approach is taken for many existing standard names. Unless the values of those parameters are always the same for all scatterometer measurements, then they need to be included with the data. If they are truly fixed values then they need to be specified in the definition, but from the discussion so far I think that is not the case.
It sounds as though it is not appropriate to say "Scattering of radiation is its deflection from its incident path without loss of energy", as in the existing definition for surface_backwards_scattering_coefficient_of_radar_wave, since John N says this is factually incorrect. I'm not sure of the origin of the sentence, but suspect that it may have crept into the definition of scattering standard names to differentiate from absorption/attenuation/quantities. However, if it is just plain wrong then perhaps we should change it to read simpy "scattering of radiation is its deflection from its incident path" in the definitions of all scattering names. Do others agree?
We need to keep the wording of the definition as consistent as possible with other similar names, so I suggest some rephrasing of what has already been proposed:
"The quantity called surface_normalized_radar_backscatter_coefficient is also commonly called the "normalized radar cross section" or "sigma naught" in the microwave remote sensing community. It is the fraction of incident power that is reflected by the surface. The surface_normalized_radar_backscatter_coefficient is measured at a single wavelength and at a single angle of incidence, which should be specified using scalar coordinate variables with standard names, respectively, of radiation_wavelength and angle_of_incidence. Scattering of radiation is its deflection from its incident path. Backwards scattering refers to the sum of scattering into all backward angles i.e. scattering_angle exceeding pi/2 radians. A scattering_angle should not be specified with this quantity. The surface_normalized_radar_backscatter_coefficient differs from the quantity surface_backwards_scattering_coefficient_of_radar_wave in that the latter does not require a radiation_wavelength and angle_of_incidence to be specified."
Does that sound OK?
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
> -----Original Message-----
> From: Jonathan Gregory [mailto:j.m.gregory at reading.ac.uk]
> Sent: 24 July 2014 15:43
> To: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] normalized_radar_backscatter_coefficient
>
> Dear David and John
>
> > So your declaration that both the radiation wavelength and scatter angle
> were essential led to my suggestion. Adopting it standardizes the method
> for citing the needed information (consistent with other standard names,
> and across users of this standard name), thereby maximizing
> interoperability.
>
> I agree that if these parameters are essential for interpretation of the data,
> and if they don't have very commonly applied standard values (which could
> be
> included in the definition as defaults), then they should be specified as
> size-one or scalar coordinate variables.
>
> Best wishes
>
> Jonathan
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Received on Fri Jul 25 2014 - 06:15:09 BST
