Dear CF-metadata list members,
Recently I have been looking into the usage of netCDF for storing model
output. Although we have agreed that netCDF4 will be the most appropriate
file format around for output of civil engineering/environmental models,
there still remain a lot of issues to resolve for storing output data of an
integrated 1D,2D,3D modelling system using staggered (possibly multiple
interconnected, structured or unstructured) grids/meshes. So, I'm very
interested in the developments regarding CF2 conventions that seem to
address most of these issues. For the time being we focus on netCDF3.6 and
CF1.0 conventions as far as they allow us to standardise.
However, when it comes to the use of standard names, I'm still not certain
what to do. Although I do understand that some kind of standardisation can
be helpful for users to understand model output from various sources and as
such it may be a valuable source of information when setting up a coupling
between model components of different origin, I feel a bit uneasy about
introducing the standard name "sea_surface_height_above_sea_level" in the
output of modelling systems that have so far been using "water level" or
similarly simple looking phrasings. So far, I have come up with two reasons
against it.
The first (I admit, subjective) reason is that as a river engineer I don't
think of the water level in a river at some distance from the coast as the
"sea_surface_height_above_sea_level"; let alone when it comes to the water
level in rural channels, flood levels in urban areas, and water levels in
sewer systems. I have seen a recent discussion on the use of the name "lake"
as an alternative for "sea" for some particular applications, but the output
of one continuous integrated model from river via estuary to sea should have
one unique name as it is one data set; we cannot differentiate between
river_surface_height and sea_surface_height. Neither should it be model run
dependent (no different name for model output depending on modelled area or
user). I expect that this subjective reason may also work the other way: you
may not want to introduce such "pollution" in the usage of the existing
names (but I am not sure about that).
The second reason is that the reference level is not everywhere the same: a
river in Tibet may be modelled using a completely different reference level
than a lowland river like the Rhine or the Mississippi. This issues is still
relevant for coastal areas as different countries tend to use different
reference levels as mean sea level, there is still a few centimetres
difference between the Dutch NAP and the German NN. Similar differences
occur in the horizontal direction when it comes to coordinate systems and
conversions.
One may thus suggest to introduce a quantity like
"water_surface_height_above_reference_level" and require some specification
of the reference level. However, the question can be extended to other
related quantities like sea_water_x_velocity and other similar quantities.
So, in the end my questions are:
(1) what are the main reasons for using standard names
(2) does it make sense to use such naming conventions for an integrated
1D,2D,3D modelling system that is used from urban areas to coastal seas and
beyond (coupled to hydrological, groundwater and/or meteorological models).
(3) or, wouldn't it be better to define a name space and some mapping as has
been suggested in relation to CF2 standards
I would be very interested in your ideas in this matter either via a reply
to this list or via a direct reply to me if you prefer.
Best regards,
Bert Jagers
technical coordinator Delft3D & SOBEK software development
WL | Delft Hydraulics
The Netherlands
http://www.wldelft.nl
Received on Tue Feb 07 2006 - 12:17:25 GMT
