Hi Alison,
*About the 'water level' vs 'sea surface height' In the case of Jeff needs would only concern ocean data, would you mind if I ask CF to introduce both? I was about to ask CF for such quantities on rivers and lakes.. *About reference datum, my opinion is that considering CF standard name is supposed to uniquely identify one geophysical field, we should ask: "are there as many standard names as there are datums?" Is the sea surface height above French Naval Chart Datum geophysically different from the sea surface height above French Naval Chart Datum for Lebanon? If the answer is yes, I guess introducing a new datum attribute in CF would be relevant. By the way if we consider the sea surface height above geoid, geoid is not exactly a datum, or became indirectly a datum: the whole quantity refers first to the geophysical information retrieved, which is the absolute ocean topography, and which is not obtained by measuring some heights and subtracting geoid heights from. It is really full of meaning in terms of ocean dynamics - and less on the way it was really measured.. *I confirm that what you explained about distinction between the same geophysical field obtained by different sensors was also applied by OSTST/Jason community. In the NetCDF product you can have 2 variables with the same standard name, but one is obtained via the onboard instrument, and the second via ECMWF forecasts. It is another illustration. Cheers, Olivier. -----Message d'origine----- De : cf-metadata-boun...@cgd.ucar.edu [mailto:cf-metadata-boun...@cgd.ucar.edu] De la part de alison.pamm...@stfc.ac.uk Envoyé : vendredi 12 février 2010 12:15 À : cf-metadata@cgd.ucar.edu Objet : Re: [CF-metadata] seeking CF name for total water column height Dear Jeff, Thank you for your standard name proposal for water column height and thanks to all who have contributed comments to this discussion. The consensus view seems to be that > sea_floor_depth_below_sea_surface is an acceptable name for this quantity and that it is consistent with the existing standard name sea_floor_depth_below_sea_level. The canonical units will be metres (m). Roy has suggested the following definition: > 'The vertical distance between the sea surface and the seabed as measured at a given point > in space including the variance caused by tides and possibly waves.' If no further comments on this name or its definition are received over the next seven days then they will be accepted in their present form for inclusion in the standard name table. You have also suggested two further standard names: water_level_with|above_reference_datum water_level_without_reference_datum For the latter name, Roy has suggested the term 'tide gauge zero' to express the lack of reference datum. Am I correct in thinking that all these quantities are referring to measurements in the open sea or coastal areas? If so, I think we should refer to sea_surface_height rather than water_level for consistency with other names. So we could have: sea_surface_height_above_reference_datum sea_surface_height_above_tide_gauge_zero. I am wondering how many different reference datums there are likely to be? You mentioned low water and highest astronomical tide but are there likely to be dozens of these quantities? If there are only a few we could consider introducing separate standard names for them as we have done with quantities such as sea_surface_height_above_reference_ellipsoid and sea_surface_height_above_geoid for example. If there are a large number of possible datums then it wouldn't be practical to introduce standard names for them all and we would need another way to record which datum is being used. Regarding the definitions, do both quantities average out the effects of waves? Nan has raised the question of how to distinguish between the same geophysical quantity measured with different sensors/sensor configurations or post-processed differently. This question has arisen in a number of contexts recently. For example, as well as sea water pressure and depth measurements, we discussed some CMIP5 proposals in which climate models were simulating cloud amounts as retrieved from two different satellite instruments. In the case of CMIP5 I believe the issue was resolved by using the same standard name for both quantities and placing them in differently named files, but a simple way of distinguishing between instruments/instrument types/retrieval algorithms in metadata would be to use the 'source' attribute which can be either global or attached to a single variable (this is already part of the CF conventions, section 2.6.2). Best wishes, Alison ------ Alison Pamment Tel: +44 1235 778065 NCAS/British Atmospheric Data Centre Fax: +44 1235 446314 Rutherford Appleton Laboratory Email: alison.pamm...@stfc.ac.uk Chilton, Didcot, OX11 0QX, U.K. -- Scanned by iCritical. _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata Cliquez sur l'url suivante https://www.mailcontrol.com/sr/qfIJjnfim1XTndxI!oX7UibJmmb6AuK6ZrMZav1w5d4ZfWlb5l2PBu6fCO3jlD4LbdPTFJ7Xke9TQ40Is2HDWw== si ce message est indésirable (pourriel).
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