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If we *do* make it mandatory, if someone doesn't want to provide it, fine. There is nothing that requires them to follow this specification. We could even have another specification, all the same but with no z required, if people are really bothered. But I think saying "we don't want to require the Z because it's just too hard for someone to fill it in with 'not available' (or 'decline to provide', for that matter)" is short sighted in multiple ways, already described in previous emails. I understand that some providers won't want to provide it, but that's true of various mandatory fields in any standard. I think this field is an important one for observational data.
Yes we will have to provide a reference for the Z, sorry everyone. That will be hard for people to grok at first but will quickly become easier, it will mostly be a matter of providing good guidance.
In response to the email below: a) data always has useful z information, whether or not it has a useful coordinateb) sea state absolutely has a z coordinate, which is the surface of the sea (yes that location changes relative to the earth geoid, the same as sea surface
temperature, and maybe the same guideline applies for that variable)c) I don't know meteorology, so I don't know if total cloud amount is from ground to space, or excludes ground fog; either way, if I'm using that data set and am not a meteorologist, I would like to know which is true (don't forget we are entering an era where data users are not experts in the field) d) the altitude of the observing station is terribly important for many analyses, and counts as the height of the measurement IF the measurement is in situ; otherwise would be nice to have e) considering half our buoy's surface "marine obs" are actually meteorology signals, and the huge interaction between marine and meteorological science, I don't think the distinction is significant for this exercise f) data writers will always do it if (1) it's a part of the standard, and (2) they are following the standard
John At 9:27 AM +0100 9/25/07, Jonathan Gregory wrote:
Dear John I completely sympathise with encouraging people to provide useful metadata. I would argue against a mandatory Z (or any) coordinate, though, as the data really might not have a useful Z coordinate. I'm guessing, but what about the sea state (its roughness due to waves)? That's a property of the sea surface one might record, but it doesn't have a height, and the ship observing it is obviously at sea level. Or the total cloud amount, say? This also doesn't relate to a particular altitude in the atmosphere. You could record the altitude of the station that observed it, but I would not say that was really a coordinate of the cloudiness itself, and again it would not be useful for marine obs. Requiring instead an "unknown" indicator or a missing data indicator strikes me as excessive, and I'm not convinced data-writers would always do it, or that it would be useful if they did. There are lots of features of CF metadata which are very valuable but optional, such as bounds, cell_methods and standard_names. Cheers Jonathan _______________________________________________ cf-pointobsconvention mailing list cf-pointobsconvention@xxxxxxxxxxxxxxxx For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/
-- ---------- John Graybeal <mailto:graybeal@xxxxxxxxx> -- 831-775-1956 Monterey Bay Aquarium Research Institute Marine Metadata Initiative: http://marinemetadata.org || Shore Side Data System: http://www.mbari.org/ssds