Spectral Band

From Earth Science Information Partners (ESIP)

Spectral Band Proposal by Tom Whittaker

Create standard_names that can be recognized by applications as being the special "band dimension" variable (similar to "time"). The name of this dimension variable would not, however, be specified, but inferred from its attributes.

Create two coordinate axis types ("wavelength" and "wavenumber") that can be recognized by the NetCDF library as defining a "spectral coordinate".

Thus, the band dimension might be declared:

<variable name="band" shape="band" type="float" >
<attribute name="standard_name" value="wavelength" />
<attribute name="units" value = "cm" />
<attribute name="_CoordinateAxisType" value = "wavelength" />

The dimension variable can then be used to dimension arrays associated with the spectral channels, e.g., wavelength boundaries for each band (channel), units, scaling, etc. The use of these (dimensioned) variables, however, would be up to the application developers rather than made part of the conventions, per se.

This would necessitate creating perhaps two new standard_names:

wavelength (there is already a "radiation_wavelength" with "electromagnetic_wavelength" as an alias, but I don't see an issue for making just "wavelength" a standard name, either. I also recognize that in most cases this refers to the center wavelength of the band/channel, and perhaps should be so designated...?).

wavenumber (There is no equivalent standard_name. Again, I imagine this would actually refer to a center wavenumber).

We would also then need to define two new coordinate axis types: wavelength and wavenumber.

For the case where people don't or can't use the dimension variable as a coordinate variable, we recommend that they use the convention name "band" as the dimension variable so that applications can at least recognize this for what it is.

In all cases, new (dimensioned) variables could then be used to specify band-specific attributes. For example:

<variable name="minimum_wavelength" shape="band" type="double">
<attribute name="units" value="cm" />