[CF-metadata] normalized_radar_backscatter_coefficient
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-- 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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