Ocean loading is the deformation of the Earth due to the weight of the ocean masses. The water in the ocean moves due to the gravitational pull of the Moon and the Sun (this is the tides), and causes the Earth, which is not completely rigid, to deform according to the varying load of the ocean’s water. The deformation is periodic, following the relative motion of Earth, Moon and Sun, however such relative motion is rather complex and thus periodicity has to be represented with several harmonic terms of different period.

Periodicity of tides around the world (graphic from NOAA)

Most commonly, the 11 first terms (i.e. those with higher amplitude) are retained to model this effect.

Ocean loading can be perceived as a periodic displacement of the station position (especially in coastal areas), as well as a periodic variation of the Earth’s gravity.

How is ocean loading taken into account in magicGNSS?

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