Hi John (N),
Thanks for the detailed explanation. I am convinced the new term is distinct. I
did not expect to redefine the old term unless one was clearly a refinement of
the other, which is not the case.
I still am concerned about the description I think you are proposing for this
term ("normalized_radar_backscatter_coefficient is also called the normalized
radar cross section, which are commonly used in the microwave remote sensing
community.") Based on your inputs, here is a second attempt:
> The fraction of incident power at a given wavelength that reaches a receiver,
> after reflection by a surface at a given reflection angle. (In microwave
> remote sensing this is also known as the 'normalized radar cross section' or
> 'sigma naught'.) Coordinate values for radiation wavelength and reflection
> angle should be given the standard names radiation_wavelength and
> scattering_angle.
This description reflects: always 1 wavelength; always 1 backward scattering
angle; and that all lost power is included in the coefficient, not simply the
surface reflectance/absorption.
If I correctly got your 3 points, the term "attenuated" applies, as it is used
elsewhere in CF: "'The attenuated backwards scattering function includes the
effects of two-way attenuation by the medium between a radar source and
receiver." Since I can't imagine needing an unattenuated backscatter
coefficient, the extra word seems unneeded for this name.
John (G)
On Jul 23, 2014, at 10:37, Niedfeldt, John C (398M-Affiliate)
<[email protected]> wrote:
> Dear John et al,
> Here are three major distinctions between the
> surface_backwards_scattering_coefficient_of_radar_wave (old) and
> normalized_radar_backscatter_coefficient (new):
> The (old) definition has the default definition as being an integral over all
> wavelengths, but the radar backscatter coefficient is always measured using
> one wavelength (new) and must always be specified.
> The part about scattering radiation having no loss in energy in the (old)
> definition is not clear, but in practice and theory energy is always lost
> once the initial wave is transmitted (indeed, it is in part the loss due to
> the ground that we are measuring)(new).
> The backscatter in the (old) definition refers to summing all backwards
> scattering angles, where in remote sensing we look at just one backscatter
> angle (new).
> And yes, if the old variable pertains to the normalized radar cross
> section--which I believe it does not--then the transmitted wavelength and
> backscatter angle (elevation angle) should be required as they are essential
> to understanding the product and being able to correlate and verify data.
>
> So yes, we could change the old definition to meet the new needs, but it
> would require a change in base assumptions that would render any current data
> using that standard name as invalid. For these reasons and more, I believe we
> should make a new standard name. The definition I have provided is accurate
> and once approved additional attributes and values can be made required to
> suit all needs for those dealing with the normalized radar backscatter
> coefficient.
>
> Sincerely,
> John
>
> --
> John Niedfeldt
> Data Engineering
> PO.DAAC, JPL
>
> From: John Graybeal <[email protected]>
> Date: Tuesday, July 22, 2014 at 3:53 PM
> To: JPL <[email protected]>
> Cc: CF Metadata List <[email protected]>, "Moroni, David F (398M)"
> <[email protected]>
> Subject: Re: [CF-metadata] normalized_radar_backscatter_coefficient
>
> John, I think we (I, anyway) were waiting for a little more clarification as
> to what was needed. Sorry for that delay. I like the name itself, makes
> sense to me.
>
> Unless I am mistaken, from your email I infer that the meaning of this is a
> narrow case of surface_backwards_scattering_coefficient_of_radar_wave. That
> description is:
>> The scattering/absorption/attenuation coefficient is assumed to be an
>> integral over all wavelengths, unless a coordinate of radiation_wavelength
>> is included to specify the wavelength. Scattering of radiation is its
>> deflection from its incident path without loss of energy. Backwards
>> scattering refers to the sum of scattering into all backward angles i.e.
>> scattering_angle exceeding pi/2 radians. Ascattering_angle should not be
>> specified with this quantity.
>
> I can't tell from the description if this item is different, so the
> description could use a little bit more meat to tease that out. Looking at
> your thread, I see this:
>
>> we are calculating sigma_naught which is the fraction of incident power that
>> is reflected by the surface. It is also very important in scatterometry to
>> record the angle of incidence as the sigma_naught changes based on the
>> incidence angle in addition to various other parameters which are essential
>> to being able to correlate data from various scatterometers.
>
> So does it work for the description could say something like the following?
> This is still similar to the other standard name, so if there are specific
> things that make the distinction clear that would be important to add. ("This
> differs from surface_backwards_...")
>
>> The fraction of incident power that is reflected by the surface. (In
>> microwave remote sensing this is also known as the 'normalized radar cross
>> section' or 'sigma naught', when produced from one angle of incidence and
>> from one wavelength.) Scattering of radiation is its deflection from its
>> incident path without loss of energy. 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.
>> Coordinates of radiation_wavelength and angle_of_incidence are used to
>> specify those baseline parameters.
>
> I'm not sure about the last part -- if they are always needed these variables
> should be required.
>
> John
>
>
>
> On Jul 22, 2014, at 14:49, Niedfeldt, John C (398M-Affiliate)
> <[email protected]> wrote:
>
>> Dear all,
>> Hello again! About two months back I sent in a request, which is referenced
>> below, in which I requested that we add the
>> ‘normalized_radar_backscatter_coefficient’ in CF. Having heard nothing to
>> the contrary, and seeing as no other standards name match our needs, we at
>> PO.DAAC will be moving forward in implementing this new standard name.
>>
>> As our newly reprocessed netCDF datasets shall soon serve as an online
>> replacement for existing datasets already in use by hundreds of
>> interdisciplinary scatterometry data users, we hope to likewise hear back
>> from you soon as to whether there is consensus on our proposed standard
>> name. If there is anything further we can do to build community consensus on
>> our proposed standard name, please let me know.
>>
>> Sincerely,
>> John
>>
>> --
>> John Niedfeldt
>> Data Engineering
>> PO.DAAC, JPL
>>
>> From: Lauret Olivier <[email protected]>
>> Date: Friday, May 30, 2014 at 8:11 AM
>> To: "[email protected]" <[email protected]>
>> Cc: JPL <[email protected]>
>> Subject: TR: normalized_radar_backscatter_coefficient
>>
>> Hi all,
>>
>> Just forwarding you some discussion we have with J. Niedfeldt about some
>> standard name for sigma naught variable. I thought the available
>> “surface_backwards_scattering_coefficient_of_radar_wave” could be used
>> considering some changes in the definition [in short I wish we could mix the
>> description of sigma naught from radar altimetry with the one from
>> scatterometers]. But it seems that the quantities are different enough to
>> introduce a new standard name (see the message below).
>>
>> Can we introduce ‘normalized_radar_backscatter_coefficient’ in CF?
>>
>> Thanks,
>>
>> Olivier
>>
>> De : Niedfeldt, John C (398M-Affiliate)
>> [mailto:[email protected]]
>> Envoyé : jeudi 29 mai 2014 21:26
>> À : Lauret Olivier
>> Objet : normalized_radar_backscatter_coefficient
>>
>> Dear Mr. Olivier,
>> After discussion with Dr. David Long of BYU and reviewing the current
>> definition with him it was determined that we do in fact need a new
>> variable. In microwave remote sensing the normalized radar cross section,
>> sigma naught, is always produced from one angle of incidence and from one
>> wavelength. I understand the desire to consolidate the number of standard
>> names and to not have duplication, but adding this standard name would
>> reduce confusion and error for many I believe. It is also general enough
>> that we can add attributes to it in the future to allow further
>> specification for various endeavors. If you have any more questions feel
>> free to contact me and thank you again for your assistance. We changed the
>> standard_name to be more descriptive.
>>
>> standard_name:
>> normalized_radar_backscatter_coefficient
>>
>> Definition:
>> normalized_radar_backscatter_coefficient is also called the normalized radar
>> cross section, which are commonly used in the microwave remote sensing
>> community.
>>
>> Canonical Units:
>> 1
>>
>>
>> Sincerely,
>> John Niedfeldt
>>
>>
>> Cliquez ici si ce message est indésirable (pourriel).
>>
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