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* It might be good to use the term "coordinate variable" instead of
"dimension variable". I believe this is the proper CF terminology.
* Thinking about the polarization issue helped me realize that the
names of the dimensions (and thus coordinate variables) are not
fixed by the CF Conventions. Perhaps there is software out there
that assumes that the time dimension will be named "time", but CF
intends that the standard_name and/or the axis attribute (and,
lacking that, the units attribute) is what uniquely identifies a
coordinate variable as having a specific interpretation. Am I
right that most of what we are really talking about here is
defining strings to use in the standard_name and axis attributes?
* Assuming that the answer to my question is "yes", is there a
single description for a string to use in the axis attribute that
would be sufficient to cover most of the different types of
radiant energy binning? Would it work to have "band" as the value
to put in the axis attribute, and then allow the standard_name and
units attributes to specialize the type of band, such as
wavelength vs polarization? (I assume that trying to put
wavelength and polarization into the same dimension is probably
not going to be a good idea.)
* As far as lower and upper limits on the wavelength for each band
are concerned, I think the existing cell_bounds convention is
sufficient for this. With some minor extensions, you could
provide rather detailed information about the sensor frequency
response for a given band.
* Other than a set of flag values, how would you indicate
polarization in a coordinate variable? Consider that you might
possibly need to include left- and right-circular polarization.
The same goes with Ken Knapp's point about applied filters and
such. The more I think about this, the more I tend toward the
idea that we probably shouldn't try to merge the different kinds
of binning into a single all-encompassing coordinate. There is a
point at which we have to go ahead and split the data into
different variables.
* There is nothing preventing you from defining dimensions and
coordinate variables for the different binnings of your image data
and storing everything into a single variable (with dimensions for
wavelength, bandwidth, polarization, applied filter, etc). It is
just the question of whether or not some portion of it will be
defined via a CF convention, and what that portion is.
Grace and peace,
Jim Biard
--
Jim Biard
Government Contractor, STG Inc.
Remote Sensing and Applications Division (RSAD)
National Climatic Data Center
151 Patton Ave.
Asheville, NC 28801-5001
jim.biard@xxxxxxxx
828-271-4900
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