[CF-metadata] dimensionless vertical coordinates

From: Yilmaz Arslanoglu <yilmaz.arslanoglu>
Date: Mon, 10 Aug 2009 16:10:19 +0200

Hi all;

I was working on a generic software design for interpretation
of NetCDF files conforming to CF conventions, and I had some
questions about dimensionless vertical coordinates.

I would like to ask my questions over a specific dimensionless coordinate type,
namely Ocean S-Coordinate type, since I guess the answers will apply
to all others.

1) "s(k) is the dimensionless coordinate at vertical gridpoint (k)"
     Does this variable refer to itself, i.e. whose "formula_terms" attribute
     is being parsed? If this is the case, why do we still include this element
     in the "formula_terms" attribute?

2) do variables which correspond to "depth" and "eta" need to have the same
    units? That is, can one of them be in meters and the other in centimeters?
    If they can be different, then doesn't the variable which
corresponds to "depth_c"
    also need to have a unit? Do we need to expect a unit for it?
Because since it is
   a scalar variable, it is not required to have one according to CF
conventions(?).

3) We know that a dimensional coordinate variable is either
monotonically increasing
    or decreasing. Will it be the case for dimensionless ones after
the formula is applied?
    That is, do these formulas and associated variable contents
guarantee that, when the
    formula is applied, we will obtain a vector of pressure or height
values, which are monotonically
    increasing or decreasing? (I would expect so since they are levels
of depth or pressure)

4) "level", "layer", and "sigma_level" are deprecated according to CF
conventions, however, still
    allowed. So how would it be possible for a generic application to
interpret them?

5) And finally, under section "2.4 Dimensions" it says that
"dimensions other than those of space
and time may be included". If this is the case, is it still possible
for a generic application to work
without being able to interpret those additional dimensions? That is,
how a could a generic application
decide on which index value to pass for that dimension without recognizing it?

Best regards,
Yilmaz
Received on Mon Aug 10 2009 - 08:10:19 BST