[CF-metadata] standard_name for coordinate variable corresponding to complex parts (real and imaginary)

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 8 Jul 2010 16:56:17 +0100

Dear Bryan and Benno

> I do *not* think it is appropriate to split the real and imaginary parts
> into two variables, since one almost never uses just one or the other,
> so it's a rather different case from splitting vector components.

I disagree still. Fourier transforms don't have to expressed as real and
imaginary components, as you know. It can equivalently be done as amplitude
and phase, and in that case it is much more likely you might use one without
the other. Of course you need both to reverse the transformation, but for
other purposes you might be interested in just one of them.

Fourier transform components as amplitude and phase have different units and
are, I would say, different kinds of geophysical quantity. I don't think it
would be right to give them a common standard name and put them in the same
data variable. Instead, consistent with what I suggested earlier, I think we
should put them in separate data variables with standard names such as
  amplitude_of_fourier_transform_wrt_time_of_sea_surface_temperature
  phase_of_fourier_transform_wrt_time_of_sea_surface_temperature
These variables have a coordinate of frequency. If it was a FT wrt longitude,
they would have standard names with wrt_longitude instead of wrt_time, and a
coordinate of, say, reciprocal_of_longitude.

Best wishes

Jonathan
Received on Thu Jul 08 2010 - 09:56:17 BST