Dear John,
I see.The definition fits for radar altimeter backscattering coefficient, but it seems to be a little different for scatterometers..
Maybe we could ask for a change and just simplify this definition so that it could benefits to the whole radar instruments? I am suggesting this because I think it would be better than picking a CF standard name depending on the kind of radar instrument.
How do you see that? Can you easily find a way to turn the definition into something that encompasses scatterometers?
Olivier
De : Niedfeldt, John C (398M-Affiliate) [mailto:John.C.Niedfeldt at jpl.nasa.gov]
Envoy? : vendredi 23 mai 2014 04:03
? : Lauret Olivier
Objet : Re: [CF-metadata] sigma_naught
David,
Here is a pretty rough copy of the email. It seems a little bold, but at the same time we clearly need something other than what they are giving us. Let me know of the alterations that you would like to make.
John
Dear Olivier,
I found the definition on the CF compliance site that says this:
surface_backwards_scattering_coefficient_of_radar_wave 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. A scattering_angle should not be specified with this quantity.
After looking over this definition, a colleague and I feel that this isn't applicable to our needs. The definition mentions and integral over all wavelengths or a singular wavelength which are both unsatisfactory for our linear chirp pulse. In addition, the backscatter is not assumed to be without loss of energy but 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. These are some of the reasons why we believe it would be best to add another standard name called sigma_naught that would be of greater benefit to the community at large.
Sincerely,
John Niedfeldt
From: Lauret Olivier <olauret at cls.fr>
Date: Tuesday, May 20, 2014 at 1:17 AM
To: JPL <John.C.Niedfeldt at jpl.nasa.gov>, "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
Subject: RE: [CF-metadata] sigma_naught
Dear John,
I confirm that 'surface_backwards_scattering_coefficient_of_radar_wave' may certainly fit your needs. As you will notice it is expressed with "1" as units, instead of dB, because dB are not literally considered as units and then are not available in UDUNITS package.
Best regards,
Olivier
Olivier Lauret
Project Engineer, CLS
Satellite Oceanography Division, Environmental Applications Dept.
E-mail: olauret at cls.fr
Tel. +33 561 394 851; Fax +33 561 393 782
De : CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] De la part de Niedfeldt, John C (398M-Affiliate)
Envoy? : lundi 19 mai 2014 17:11
? : cf-metadata at cgd.ucar.edu
Objet : [CF-metadata] sigma_naught
Dear all,
Radar Scatterometers, such as QuikSCAT, are used to measure the winds over the oceans, Arctic and Antarctic ice age, track icebergs, among other things by measuring a value called sigma naught, also known in the radar community as the normalized radar cross-section or backscatter coefficient. Due to a significant effort to reprocess multiple sigma naught datasets to netCDF format, which shall be hosted at the Physical Oceanography Distributed Active Archive Center (
http://podaac.jpl.nasa.gov <
http://podaac.jpl.nasa.gov/> ) for public distribution, I propose the following standard_name definition be added to the CF standard name:
standard_name:
sigma_naught
Definition:
sigma_naught refers to the normalized radar cross section, also known in the microwave remote sensing community as the backscatter coefficient.
Canonical Units:
dB
Sincerely,
John Niedfeldt
Cliquez ici <
https://www.mailcontrol.com/sr/MZbqvYs5QwJvpeaetUwhCQ==> si ce message est ind?sirable (pourriel).
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Received on Fri May 23 2014 - 07:10:32 BST
