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[CF-metadata] normalized_radar_backscatter_coefficient

From: Niedfeldt, John C <John.C.Niedfeldt>
Date: Mon, 4 Aug 2014 21:46:22 +0000

Dear all,
Have there been any more developments with the
normalized_radar_backscatter_coefficient? If you haven?t receive my other
two emails with details on the new, more user-friendly definition of the
standard name then please let me know.

Sincerely,
John

--
John Niedfeldt
Data Engineering
PO.DAAC, JPL
On 7/23/14, 9:32 PM, "John Graybeal" <john.graybeal at marinexplore.com>
wrote:
>Hi David,
>
>Thanks for the question. Constant coordinate variables are hopefully not
>a big deal -- they can be easily specified as scalar coordinate
>variables, as noted in the example here:
>http://cfconventions.org/Data/cf-convetions/cf-conventions-1.7/build/cf-co
>nventions.html#scalar-coordinate-variables.
>
>That's an example for analysis time and pressure level, but it's OK to
>use coordinate variables for any critical reference variable. (Chapter 4:
>"Coordinate types other than latitude, longitude, vertical, and time are
>allowed." Incidentally, the text in reference [1] was proposed as a
>replacement for that sentence in http://kitt.llnl.gov/trac/ticket/100,
>which has been accepted but not implemented.)
>
>I had to search the archives to fully understand the motivation, here's
>what I found (ooh, FAQ question!):
>  (1) To locate the data in an axis other than space or time. [1]
>  (2) To provide a consistent way to specify the value of a certain other
>parameter, or even multiple parameters; if the parameter is unvarying, it
>can be specified as a scalar. [2]
>
>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.
>
>By all means reply further if this seems problematic, I'm at the edge of
>my experience but others can jump in.
>
>John
>
>[1] On Apr 11, 2013, at 12:45, Jonathan Gregory
><j.m.gregory at reading.ac.uk> wrote:
>
>> The commonest use of coordinate variables is to locate the data in
>>space and
>>  time, but coordinates may be provided for any other continuous
>>geophysical
>>  quantity (e.g. density, temperature, radiation wavelength, zenith
>>angle of
>>  radiance, sea surface wave frequency) or discrete category (see
>>Section 4.5,
>>  "Discrete axis", e.g. area type, model level number, ensemble member
>>number)
>>  on which the data variable depends.
>
>
>[2] On Dec 24, 2010, at 13:26, Jonathan Gregory
><j.m.gregory at reading.ac.uk> wrote:
>
>>  We quite often recommend, for instance in connection with particular
>>standard names,
>> that the value of a certain other parameter could be specified, e.g. a
>> radiation_wavelength for radiative quantities. Scalar coord vars are a
>>neat
>> way to do this. They are something between multivalued coord vars and
>> attributes in terms of function: easier than coord vars, and more
>>powerful
>> than attributes because they can themselves have attributes.
>
>[3] 
>
>
>On Jul 23, 2014, at 17:39, Moroni, David F (398M)
><David.F.Moroni at jpl.nasa.gov> wrote:
>
>> Hi John (G),
>> 
>> John (N) and myself are working together on this effort.
>> 
>> Thanks for your inputs here.
>> 
>> In general, I agree with the first part of your revision of the
>>description, but I don't suggest including a reference to the coordinate
>>values for the other standard names as you've suggested, namely
>>"radiation_wavelength" and "scattering_angle", simply because this type
>>of measurement assumes: 1) constant wavelength and 2) constant
>>scattering angle. I simply don't follow your reasoning for why such
>>coordinate values would be needed given the nature of these values being
>>constant. Can you provide some rationale as to why we would want to list
>>these as coordinate values?
>> 
>> Cheers,
>> David
>> 
>> ==================================================
>> David Moroni
>> Ocean Wind and Scatterometry Data Engineer
>> Physical Oceanography Distributed Active Archive Center
>> Jet Propulsion Laboratory
>> 4800 Oak Grove Dr
>> M/S 158-242
>> Pasadena, CA 91109
>> Phone:  818.354.2038
>> Fax:  818.353.2718
>> ==================================================
>> 
>> From: John Graybeal <john.graybeal at marinexplore.com>
>> Date: Wednesday, July 23, 2014 3:52 PM
>> To: "Niedfeldt, John C (398M-Affiliate)" <John.C.Niedfeldt at jpl.nasa.gov>
>> Cc: CF Metadata List <cf-metadata at cgd.ucar.edu>, David F Moroni
>><David.F.Moroni at jpl.nasa.gov>
>> Subject: Re: [CF-metadata] normalized_radar_backscatter_coefficient
>> 
>>> 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)
>>><John.C.Niedfeldt at jpl.nasa.gov> 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 <john.graybeal at marinexplore.com>
>>>> Date: Tuesday, July 22, 2014 at 3:53 PM
>>>> To: JPL <John.C.Niedfeldt at jpl.nasa.gov>
>>>> Cc: CF Metadata List <cf-metadata at cgd.ucar.edu>, "Moroni, David F
>>>>(398M)" <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> 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>
>>>>> Date: Friday, May 30, 2014 at 8:11 AM
>>>>> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
>>>>> Cc: JPL <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
>>>>>  
>>>>> 
>>>>> Cliquez ici si ce message est ind?sirable (pourriel).
>>>>> 
>>>>> _______________________________________________
>>>>> CF-metadata mailing list
>>>>> CF-metadata at cgd.ucar.edu
>>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>> 
>>>> _______________________________________________
>>>> CF-metadata mailing list
>>>> CF-metadata at cgd.ucar.edu
>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>> 
>
Received on Mon Aug 04 2014 - 15:46:22 BST

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