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I want to model future coastal flooding caused by sea-level rise under the latest IPCC scenarios at global scale. To this end, I use the Copernicus Digital Elevation Model (Copernicus DEM: https://spacedata.copernicus.eu/fr/collections/copernicus-digital-elevation-model). Silly me, I thought that the elevation height of 0m of the Copernicus DEM was the mean sea level of the data acquisition period of this DEM, but I have been told that it might not be the case.

Does the elevation height of 0m of the Copernicus DEM correspond to mean sea level of the data acquisition period of this DEM (i.e., 2011-2015)? Does it correspond to mean sea level of the vertical reference datum of this DEM (i.e., Earth Gravitational Model 2008 - EGM 2008)? Or does it correspond to an older historical reference?

In the Copernicus DEM metadata it is written: "Ocean water bodies are set to the elevation height of 0m, including all seas, inlets, fjords and any other extensions of the ocean."

I need to know what this 0m elevation height corresponds to and at what elevation is the mean sea level on this DEM.

Thank you!

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    $\begingroup$ Your link is dead. $\endgroup$
    – Spencer
    May 24 at 22:25
  • $\begingroup$ I just updated it. $\endgroup$
    – Circus pygargus
    May 26 at 7:34

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From the website you linked:

Coordinate Reference System: Horizontal WGS84-G1150 (EPSG 4326) (DGED & DTED format), (EPSG 3035) for continental Europe and UTM , (EPSG 32740, 32622, 32738, 32620) for the French DOMs (INSPIRE format), Vertical EGM2008 (EPSG 3855)

So the vertical datum is EGM2008, which is a reference geoid (Pavlis et al., 2012). It doesn't exactly correspond with mean sea level (MSL). There are local adjustments that need to be applied to change from 0m EGM2008 to MSL. I usually refer to the explanations at the VDatum site. geoid VDatum

They provide a calculator for the United States (https://vdatum.noaa.gov/vdatumweb/vdatumweb). For instance, for a point at 41.2 N and 69.5 W, that is 0m when using EGM2008, the height when referenced to MSL is 0.379m.

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    $\begingroup$ Thank you for this quick and detailed answer! Unfortunately I am not working on the US but on the Mediterranean. Do you know if there is a calculator for this region or for the global scale? I understand that the reference geoid does not exactly correspond to sea-level but it is defined as a "set of geopotential coefficients used in a spherical harmonic expansion to create a global potential surface to coincide with Mean Sea Level (MSL)." (earth-info.nga.mil/index.php?dir=wgs84&action=wgs84). So it might still be a good estimation? $\endgroup$
    – Circus pygargus
    Nov 2, 2022 at 12:50
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    $\begingroup$ It all depends on what you are trying to do in your coastal application. If you are looking at currents in the coastal ocean, then a difference of a few cm is not going to have a big effect. On the other hand, for your application, the changes in future inundation are on the same order of magnitude as the differences in datum. I'm not familiar with any correction for the Mediterranean or global scale. I imagine somebody may have calculated it, as it is common practice, but I don't know who. You could try to use it as MSL based on the statement you found and see if somebody has anything better $\endgroup$
    – arkaia
    Nov 2, 2022 at 14:13
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    $\begingroup$ Many thanks for your answer! I think I might use the 0m elevation height of the Coastal DEM as MSL at first and look for a correction for my study zone at the same time. $\endgroup$
    – Circus pygargus
    Nov 3, 2022 at 10:08
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What I would do is cast the data into a new projection (if absolutely necessary).

In particular, once you have a global model tied to a known reference ellipsoid you can convert that into local projection which can follow the local mean sea level more precisely.

Personally, I'd use pyProj.

For a more complete example, see e.g. this answer from GIS StackExchange, where data is converted from a given elevation system to another using the EPSG-codes.

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Here is the answer from the Support Team of Copernicus:

The definition of the 0 m elevation for ocean areas is not dependent on the acquisition date of the input images. Please note that the Copernicus DEM is quality-based combination of multiple acquisitions which, from our understanding, prevents to focus on just a single scene and the ocean extent present at that day. Elevation 0m in the Copernicus DEM is more general and referring to the mean sea level of the vertical reference datum of this DEM (i.e., Earth Gravitational Model 2008 - EGM 2008).

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