[CF-metadata] normalized_radar_backscatter_coefficient

From: Niedfeldt, John C <John.C.Niedfeldt>
Date: Wed, 23 Jul 2014 17:37:23 +0000

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):

  1. 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.
  2. 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).
  3. 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 <john.graybeal at marinexplore.com<mailto:john.graybeal at marinexplore.com>>
Date: Tuesday, July 22, 2014 at 3:53 PM
To: JPL <John.C.Niedfeldt at jpl.nasa.gov<mailto:John.C.Niedfeldt at jpl.nasa.gov>>
Cc: CF Metadata List <cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>>, "Moroni, David F (398M)" <David.F.Moroni at jpl.nasa.gov<mailto:David.F.Moroni at jpl.nasa.gov>>
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) <John.C.Niedfeldt at jpl.nasa.gov<mailto:John.C.Niedfeldt at jpl.nasa.gov>> 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 <olauret at cls.fr<mailto:olauret at cls.fr>>
Date: Friday, May 30, 2014 at 8:11 AM
To: "cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>" <cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>>
Cc: JPL <John.C.Niedfeldt at jpl.nasa.gov<mailto:John.C.Niedfeldt at jpl.nasa.gov>>
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:John.C.Niedfeldt at jpl.nasa.gov]
Envoy? : jeudi 29 mai 2014 21:26
? : 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
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Received on Wed Jul 23 2014 - 11:37:23 BST