Understanding Altitude: Does a 0m Elevation Height in Copernicus DEM Signify Mean Sea Level?

Digital Elevation Models (DEMs) provide a representation of the Earth’s surface that is essential for a wide range of applications, from mapping and environmental studies to engineering and urban planning. The Copernicus DEM is a global digital elevation model produced by the European Space Agency (ESA) that provides high-resolution elevation data for the entire Earth’s surface. One of the most frequently asked questions about the Copernicus DEM is whether an elevation of 0 m in the model corresponds to mean sea level. In this article, we aim to answer this question by exploring the concept of mean sea level, how it is defined, and how it compares to the 0m elevation in the Copernicus DEM.

What is mean sea level?

Mean sea level (MSL) is the average height of the ocean surface over a period of time. It is usually defined as the average height of the sea surface over a 19-year period known as the National Tidal Datum Epoch (NTDE), which is recalculated every few decades by the National Oceanic and Atmospheric Administration (NOAA) in the United States. Other countries have their own NTDEs based on their own tidal observations.

The MSL is an essential parameter for many coastal and oceanographic applications, such as navigation, oceanography, and climate research. It is used as a reference level for measuring the height of tides, waves, and storm surges, and for predicting coastal flooding and erosion.

How is the Copernicus DEM created?

The Copernicus DEM is generated from satellite radar altimetry data acquired by the Sentinel-1 mission, which measures the distance between the satellite and the Earth’s surface. By combining these measurements with precise orbital information, the Copernicus DEM is able to provide a highly accurate representation of the elevation of the Earth’s surface.

The Copernicus DEM is referenced to the WGS84 ellipsoid, a mathematical model of the Earth’s shape that approximates the Earth as an oblate spheroid. The ellipsoid is used as a reference surface for geodetic measurements and is defined by its semimajor and semiminor axes.

Does an elevation of 0m in the Copernicus DEM mean mean sea level?

The short answer is no, a 0m elevation in the Copernicus DEM does not necessarily correspond to mean sea level. The Copernicus DEM is referenced to the WGS84 ellipsoid, which is a mathematical model of the shape of the Earth and is not directly related to the ocean surface. Therefore, an elevation of 0 m in the Copernicus DEM represents the elevation above the WGS84 ellipsoid, not the ocean surface.
However, it is possible to convert elevations in the Copernicus DEM to heights above mean sea level using geoid models. A geoid is a mathematical model of the Earth’s gravity field that approximates the shape of the ocean surface. Geoid models are used to convert ellipsoidal heights to heights above mean sea level by taking into account the variations in the Earth’s gravity field caused by the uneven distribution of mass in the Earth’s interior.

The European Gravity Service for Improved Emergency Management (EGSIEM) provides a highly accurate global geoid model that can be used to convert heights in the Copernicus DEM to heights above mean sea level. By using the EGSIEM geoid model, it is possible to obtain a more accurate representation of the elevation of the Earth’s surface with respect to the ocean surface.

Conclusion

In summary, an elevation of 0 meters in the Copernicus DEM does not correspond to mean sea level. The Copernicus DEM is referenced to the WGS84 ellipsoid, which is a mathematical model of the shape of the Earth and is not directly related to the ocean surface. However, it is possible to convert elevations in the Copernicus DEM to heights above mean sea level using geoid models such as the EGSIEM geoid model. This provides a more accurate representation of the elevation of the Earth’s surface relative to the ocean surface. This is particularly important for coastal and oceanographic applications where the height of the ocean surface relative to the Earth’s surface is critical.

It should be noted that the accuracy of the conversion from ellipsoidal heights to heights above mean sea level depends on the quality of the geoid model used. Therefore, it is important to use the most current and accurate geoid models available for accurate height conversions.

Overall, understanding the relationship between the Copernicus DEM and mean sea level is important for a number of applications that require accurate elevation data. By using appropriate geoid models, it is possible to obtain a more accurate representation of the elevation of the earth’s surface relative to the ocean’s surface, which is critical for coastal and oceanographic studies, as well as many other applications that rely on accurate elevation data.

FAQs

1. What is a Digital Elevation Model (DEM)?

A Digital Elevation Model is a digital representation of the earth’s surface that shows the elevation of each point on the ground. It is typically created by using remote sensing techniques such as radar or lidar to measure the elevation of the earth’s surface.

2. What is mean sea level?

Mean sea level is the average height of the ocean’s surface over a period of time. It is usually defined as the average height of the sea surface over a 19-year period, known as the National Tidal Datum Epoch (NTDE), which is recalculated every few decades by the National Oceanic and Atmospheric Administration (NOAA) in the United States.

3. How is the Copernicus DEM produced?

The Copernicus DEM is generated from satellite radar altimetry data acquired by the Sentinel-1 mission, which measures the distance between the satellite and the earth’s surface. By combining these measurements with precise orbital information, the Copernicus DEM is able to provide a highly accurate representation of the earth’s surface elevation.

4. Does a 0m elevation height in the Copernicus DEM correspond to mean sea level?

No, a 0m elevation height in the Copernicus DEM does not correspond to mean sea level. The Copernicus DEM is referenced to the WGS84 ellipsoid, which is a mathematical model of the earth’s shape and is not directly related to the ocean’s surface. Therefore, a 0m elevation height in the Copernicus DEM represents the elevation above the WGS84 ellipsoid, not the ocean’s surface.

5. How can elevations in the Copernicus DEM be converted to heights above mean sea level?

Elevations in the Copernicus DEM can be converted to heights above mean sea level by using geoid models. A geoid is a mathematical model of the earth’s gravity field that approximates the shape of the ocean’s surface. Geoid models are used to convert ellipsoidal heights to heights above mean sea level by taking into account the variations in the earth’s gravity field caused by the uneven distribution of mass in the earth’s interior.

6. What is the EGSIEM geoid model?

The European Gravity Service for Improved Emergency Management (EGSIEM) provides a high-accuracy global geoid model that can be used to convert elevations in the Copernicus DEM to heights above mean sea level. By using the EGSIEM geoid model, it is possible to obtain a more accurate representation of the elevation of the earth’s surface with respect to the ocean’s surface.

7. Why is understanding the relationship between the CopernicusDEM and mean sea level important?

Understanding the relationship between the Copernicus DEM and mean sea level is important for a range of applications that require accurate elevation data. By using appropriate geoid models, it is possible to obtain a more accurate representation of the elevation of the earth’s surface with respect to the ocean’s surface, which is crucial for coastal and oceanographic studies, as well as for many other applications that rely on precise elevation data. This is particularly important for predicting coastal flooding and erosion, as well as for navigation and oceanographic research.