NTR for new datum to support remodeling of sea level parameter codes

[gwemon]

The following entries are needed in S20:

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Proposed prefLabel	Proposed definition
unspecified datum	The datum is not specified.
Mean Sea Level datum	A vertical datum based on the arithmetic mean of hourly heights observed over the National Tidal Datum Epoch. Shorter series are specified in the name; e.g. monthly mean sea level and yearly mean sea level. Adapted from https://tidesandcurrents.noaa.gov/datum_options.html
Lowest Astronomical Tide datum	A vertical datum based on the elevation of the lowest predicted astronomical tide expected to occur at a specific tide station over the time period of 40 years. The 40 years period will include 2 National Tidal Datum Epoch periods. This time period will be updated every 20 years. The present values are based on the time period of 2000-2040. Adapted from https://tidesandcurrents.noaa.gov/datum_options.html
Rijkswaterstaat Mean Sea Level	A vertical datum based on the mean sea level for a period of minimal 2 days converted to a many-year average based on measurements taken at the specified location.
NAP datum	A vertical datum used in large parts of Western Europe. Also known as Amsterdam Ordnance Datum. NAP stands for Normaal Amsterdams Peil.
relative to instrument zero	The measurement is given relative to the instrument's zero.
Normal Low Water datum	Not available
Okioc Reference Level datum	Not available
Ordnance Datum Malin	A vertical datum based on the mean sea level of the tide gauge at Malin Head, County Donegal. It was adopted as the national datum in 1970 from readings taken between 1960 and 1969 and all heights on national grid maps are measured above this datum.
UK Admiralty Chart Datum	A vertical datum based on the low water plane specified by UK Admiralty. This approximates to Lowest Astonomical Tide but the two are not exactly the same in some geographical areas.
Mean Water Height	Not available
Ordnance Datum Newlyn	A vertical datum based on the mean sea level at Newlyn in Cornwall averaged between 1915 and 1921 used for the elevation of the zero metres contour on UK Ordnance Survey maps.
Chart Datum	The measurement is referenced to an unspecified chart datum.

[gwemon]

Hi @danibodc I am assigning this to you as it goes together with the sea-floor depth remodelling discussion. We need to complete the definitions and add the terms to S20.

[gwemon]

New terms created in S20 and queued for publication on the NVS.

[gwemon]

And corresponding S29 terms also created.

[gwemon]

All new terms now available from the S20 vocab on the NVS: http://vocab.nerc.ac.uk/collection/S20/current/