Tech UPTechnologyGeoid: the true shape of the Earth

Geoid: the true shape of the Earth

How would you stay if we told you that the Earth is not round ? No, we are not talking about an unscientific conspiracy theory, like flat Earth.

This image shows as accurate a representation as possible of the Earth’s gravitational field. But be careful: this is not the true shape of the Earth, but the shape the planet would have if it were completely flooded with water in the absence of tides and currents, shaped only by gravity.

The gravity map obtained by the GOCE mission of the European Space Agency (ESA) is what scientists call a geoid. The colors in the image represent the areas of maximum gravitational field. Blue represents low values and red and yellow represent high values.

As accurate as possible a model of the Earth’s geoid is essential to obtain accurate measurements of ocean circulation, sea level change, and land ice dynamics. The geoid is also used as a reference surface from which to map the topographic features of the planet. Additionally, a better understanding of the variations in the field of gravity will lead to a deeper understanding of the Earth’s interior, such as the physics and dynamics associated with volcanic activity and earthquakes.

The Earth is not a perfect sphere: Earth’s gravity causes an uneven distribution of masses on Earth. From a geometric point of view, the Earth can be considered as a sphere of radius 6 371 km and, in second approximation, as an ellipsoid of revolution.

The ellipsoid of revolution was adopted as an “international ellipsoid” by the General Assembly of the International Geodetic and Geophysical Union (UGGI), held in Madrid in 1924. ESA’s GOCE mission has measured high-precision gravity gradients thanks to which Global models of the Earth’s gravity field have been reproduced.

The geoid (the surface of equal gravitational potential of a hypothetical ocean at rest) serves as a classic reference for all topographic features. The precision of its determination is important for topography and geodesy, and in studies of the Earth’s interior processes, ocean circulation, ice movement, and sea level change. In addition, it serves to gain a better understanding of the variations in the Earth’s gravitational field, leading to a deeper understanding of the Earth’s interior, its physics and the dynamics associated with volcanic activity and earthquakes.

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