[CF-metadata] water level with/without datum

Jeff deLaBeaujardiere Jeff.deLaBeaujardiere at noaa.gov
Fri Feb 12 10:56:38 MST 2010

Thank you for the discussion and current status regarding sea_floor_depth_below_sea_surface as a new standard name. I have changed the subject line of this email to focus on the other names we discussed. I have also CCed our local water level expert (Andrea Hardy from NOAA CO-OPS); my replies are based on limited knowledge.

alison.pamment at stfc.ac.uk wrote:
> 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.

I suppose you mean the latter name could be something like water_level_relative_to_tide_gauge_zero ?
I believe that at NOAA we use the term "station datum" to refer to measurements relative only to the station (which might be a tide gauge or not), so perhaps one of these would be better:


I like the use of the word "above" because it indicates the sign of the value, but that's just a personal preference.

> 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.

My understanding is that water level stations may be associated with rivers or the US Great Lakes, so "sea surface" would not be ideal.

> 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

Possible datums include at least International Great Lakes Datum (IGLD), mean high water (MHW), mean lower low water (MLLW), mean sea level (MSL), and NAVD88.

I believe our preference would be *not* to include the datum name in the standard name, so that the user can request the datum of their choice.

Andrea: I see that on your server Station Datum is among the choices. Are you sure it wouldn't be better to have a single name like water_level_relative_to_datum, with station datum merely being one of the options?

> Regarding the definitions, do both quantities average out the effects of waves?

I don't know. Andrea?

Regards to all from snowy Washington,
Jeff DLB

Jeff de La Beaujardière, PhD
Senior Systems Architect, Data Integration Framework
Integrated Ocean Observing System (IOOS) Program Office
National Oceanic and Atmospheric Administration
1100 Wayne Ave #1225, Silver Spring MD 20910 USA
+1 301 427 2427
Jeff.deLaBeaujardiere at noaa.gov 

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