Aleksander:
This has come up before on CF-satellite. checkout:
http://www.unidata.ucar.edu/mailing_lists/archives/cf-satellite/2011/msg00025.html
very respectfully,
randy
----------------------------------------
From: "Aleksandar Jelenak - NOAA Affiliate" <aleksandar.jelenak@xxxxxxxx>
Sent: Thursday, April 04, 2013 3:09 PM
To: "cf-metadata@xxxxxxxxxxxx" <cf-metadata@xxxxxxxxxxxx>
Subject: [CF-metadata] New CoordinateType: Spectral?
Dear All, I know this will likely end up as a trac ticket but would like first
to gauge the community's opinion about defining a new coordinate type.
Satellite data originates as measurements at a number of intervals of the
electromagnetic spectrum. These intervals are commonly referred to as bands or
channels. Deciding on how to store the band information is one of the key
issues toward a standardized representation for satellite data. The convention
seems to allow storing of band information either as a numerical coordinate
variable or as a string auxiliary coordinate variable. When I open such a file
in Unidata's ToolsUI software (the CoordSys tab) and select Parse Info, this is
reported: <userAdvice>Coordinate Axis band does not have an assigned
AxisType</userAdvice> Following this advice I have two questions: 1) What would
be the benefits of having a coordinate type for describing satellite bands?
Let's call this new type "spectral" for now. 2) Can the same coordinate type be
assigned to both numerical and string variables? Such variables will not appear
in the same file. String band information will cover cases where purely
numerical band information is not sufficient to describe different bands, like
for passive microwave instruments. I have included two examples in the P.S.
section below to illustrate the concept. -Aleksandar P.S. Variant #1: Band
information as a numerical coordinate variable dimensions: along_track =
<integer> ; across_track = <integer> ; band = <integer> ; variables: short
along_track(along_track) ; along_track:axis = "Y" ; short
across_track(across_track) ; across_track:axis = "X" ; float band(band) ;
band:standard_name = "sensor_band_central_wavelength" ; // proposed standard
name in Nov 2012 band:units = "um" ; float lat(along_track, across_track) ;
lat:standard_name = "latitude" ; lat:units = "degrees_north" ; float
lon(along_track, across_track) ; lon:standard_name = "longitude" ; lon:units =
"degrees_east" ; double time(along_track) ; time:standard_name = "time" ;
time:units = "<units> since <datetime string>" ; time:calendar = "gregorian" ;
float swath_band_data(along_track, across_track, band) ;
swath_band_data:coordinates = "lon lat time band" ; Variant #2: Band
information as a string auxiliary coordinate variable dimensions: along_track =
<integer> ; across_track = <integer> ; band_enum = <integer> ; band_strlen =
<integer> ; variables: short along_track(along_track) ; along_track:axis = "Y"
; short across_track(across_track) ; across_track:axis = "X" ; char
band(band_enum, band_strlen) ; band:standard_name = "sensor_band_identifier" ;
// proposed standard name in Nov 2012 float lat(along_track, across_track) ;
lat:standard_name = "latitude" ; lat:units = "degrees_north" ; float
lon(along_track, across_track) ; lon:standard_name = "longitude" ; lon:units =
"degrees_east" ; double time(along_track) ; time:standard_name = "time" ;
time:units = "<units> since <epoch>" ; time:calendar = "gregorian" ; float
swath_band_data(along_track, across_track, band_enum) ;
swath_band_data:coordinates = "lon lat time band" ;
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