Vertical datum

[saeed-moghimi-noaa]

Australian tide stations

Hi All,
Following our discussion about the Australian tide stations, the Marine and Antarctic Environmental Prediction Services/ the Bureau of Meteorology in Australia shared the following information:
Here is the Australian Baseline Sea Level Monitoring Project File information and Instructions webpage and if you click, for instance, on Darwin station, you will see the metadata, and you can find the vertical datum, which is the Lowest Astronomical Tide (LAT). Here you see the list of data and if you click on Hourly Sea Level and Meteorological Data, you can extract the data.

The elevation data from this table is the same as what searvey extracts from the IOC, which is great. As I promised, I compare two data sets for Darwin and those are identical. So it means that the vertical datum for IOC data is LAT after 2010 (for Darwin).

In order to convert it to the LMSL, the Australian Baseline Sea Level Monitoring Project Monthly Sea Level and Meteorological Statistics is the great webpage.
If you choose any station, it will give you monthly mean sea level from 1991 to 2021. This is the number that we need to subtract from what we extract from IOC through the searvey to convert the vertical datum from LAT to LMSL if we need to.

Please let me know if you have any questions or clarification.

Cheers,
Mojy

--

Mojgan (Mojy) Rostaminia, Ph.D.

Pronouns: She/Her/Hers (why is this important?)

Physical Scientist, Coastal Marine Modeling Branch
NOAA/NOS/OCS/Coast Survey Development Laboratory
1315 East West Hwy, SSMC3, Silver Spring, MD 20910

(302) 648-6436

[saeed-moghimi-noaa]

And to follow-up on Carola's question re: resolving relevant VDatum grids:

There is polygon geometry and metadata included in each VDatum marine grid region folder: i.e., currently directories/files of the form _8301/_8301.[bnd,kml,met], per NOAA's National Tidal Datum Epoch (NTDE) 1983-2001. The VDatum client application uses that geometry to restrict what "additional coverage" that may otherwise be indicated by the raster grid files (tss.gtx, mhw.gtx, mllw.gtx, etc.); note: the coverage of each grid may not be consistent with respect to each other).

The VDatum KML includes 4 feature-polygon layers:
*_8301.bnd: Approximate minimum bounding regular rectangle
masked-out - *_8301.kml: Approximate polygon of non-valid [.gtx] area
[sic] none-tidal - *_8301.kml: Approximate polygon of non-tidal area (where a non-tidal grid may or may not be available; e.g. a Low Water Datum (lwd.gtx) defined by NOAA as 0.5 ft below LMSL, or some other reference plane or datum .gtx file possibility (Columbia River Datum: vdatum_4.4_20220315/CRD/crd.gtx).
valid-transform - *_8301.kml: Approximate polygon of valid ortho-tidal grids

gdal supports the .gtx raster format, so you can view it as a raster in (say) QGIS through simple drag-n-drop—and in context with the coverage supported by the VDatum software per the relevant KML file polygons, layers valid-transform and masked-out.

Jack L. Riley
Coast Survey Development Lab