Hello Derrick,
I did not know about this SOS project on tide gauges, it's really interesting!
I remember a similar issue was raised a few month ago..
As far as I remember, the idea was that datum instance should not be supported internally, but using URIs. (for people who remember that topic, please correct me if I am telling stupid things)
One problem that I know is that usually the reference database used for datum is EPSG, and sometimes the reference you need is not provided as an EPSG code.
In the case of the reference ellipsoid, I faced this problem with Jason-2 satellite altimetry datasets..What was done is simply add some global attributes that precise 1) semi-major axis 2) flattening coefficient for reference ellipsoid.
I hope this will help you.
Best regards,
Olivier.
-----Message d'origine-----
De?: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] De la part de Derrick Snowden
Envoy??: vendredi 27 f?vrier 2009 18:07
??: CF-metadata email list
Objet?: [CF-metadata] Standard Names: sea level from tide gauge stations
All,
I'm trying to determine the right way to encode tide gauge data in CF.
I believe that the three applicable standard names are
sea_surface_height_above_geoid
sea_surface_height_above_sea_level
sea_surface_height_above_reference_ellipsoid
I don't think that we want to commit to any one of them, because the data delivery service will be flexible enough to provide the data referenced to various vertical datum so that the standard name in the file might change based on a user request. I'm wondering how the vertical datum is associated with the measurement indicated by the standard name. For example, sea_surface_height_above_sea_level, implies a datum of mean sea level. However, what if the user chooses another reference sea level average such as MLLW, mean lower low water? Can this be specified as an ancillary measurement or is it a coordinate measurement? Similarly, how should the ellipsoid be specified in sea_surface_height_above_reference_ellipsoid? Although this question is probably more relevant to satellite data than tide gauges.
As an example you can see the NOAA National Water Level Observing Network maintained by the NOAA National Ocean Service below. They are creating a Sensor Observation Service that serves both observed and predicted sea level data from tide gauge stations. The resulting data is served using a GML dialect which allows for references to external dictionaries specifying the vertical datum. Can something similar be done in CF?
http://opendap.co-ops.nos.noaa.gov/ioos-dif-sos/
click Try Me (GET/POST) next to Preliminary Water Level Data (Latest) for an example interface that provides the data in gml/xml. Inside the file you'll see the reference to VerticalDatum.
Thanks for your time.
Derrick
--
Derrick Snowden
NOAA Climate Program Office, Climate Observation Division 1100 Wayne Avenue, Suite 1202 Silver Spring, MD 20910 USA Tel 1-301-427-2464 Fax 1-301-427-0033
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Received on Tue Mar 03 2009 - 10:29:26 GMT
