[CF-metadata] normalized_radar_backscatter_coefficient
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-- John Niedfeldt Data Engineering PO.DAAC, JPL On 8/5/14, 5:14 AM, "alison.pamment at stfc.ac.uk" <alison.pamment at stfc.ac.uk> wrote: >Dear John, > >Thank you for contacting the mailing list again. I think we may not have >received your most recent emails (the last one from yourself that appears >in the mailing list archives is dated 29th July and Jonathan Gregory >responded on 30th July). If there have been other emails in the >intervening period, please could you send them to the list again. I >should add that I concur with the comments in Jonathan's email regarding >the use of coordinate variables, rather than attributes, to describe >geophysical information in the CF conventions. > >Please feel free to contact me directly if you are having problems >sending to the list, or if you have any other queries regarding the >status of your proposal. > >Best wishes, >Alison Pamment > >------ >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: Niedfeldt, John C (398M-Affiliate) >> [mailto:John.C.Niedfeldt at jpl.nasa.gov] >> Sent: 04 August 2014 22:46 >> To: John Graybeal; CF Metadata List >> Subject: Re: [CF-metadata] normalized_radar_backscatter_coefficient >> >> 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 >> >>> >> > >> >> _______________________________________________ >> CF-metadata mailing list >> CF-metadata at cgd.ucar.edu >> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadataReceived on Tue Aug 05 2014 - 11:42:01 BST
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