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Gravity, Magnetic and Geodynamic measurements

The geoid is the surface of equal gravitational potential at mean sea level, and reflects the irregularities in the Earth’s gravity field at the planet’s surface caused by the inhomogeneous mass and density distribution in the interior. Such measurements are vital for quantitative determination – in combination with satellite altimetry – of ocean currents, improved global height references, estimates of the thickness of the polar ice sheets and its variations, and estimates of the mass/volume redistribution of fresh water in order to better understand the hydrological cycle.
Detailed MeasurementDescription*InstrumentsTimeline
Crustal MotionChanges in time of the position and height of the Earth’s plates. Indicative of the lithosphere dynamics, thus useful for earthquake prediction - Physical unit: [ mm/y ] - Accuracy unit: [ mm/y ].3 instruments
Crustal plates positioningBasic for monitoring the evolution of the lithosphere dynamics - Physical unit: [ cm ] - Accuracy unit: [ cm ].2 instruments
GeoidEquipotential surface which would coincide exactly with the mean ocean surface of the Earth, if the oceans were in equilibrium, at rest, and extended through the continents (such as with very narrow channels) - Physical unit: [ cm ] - Accuracy unit: [ cm ].5 instruments
Gravity fieldIndicative of the statics and dynamics of the lithosphere and the mantle - Physical unit: [ mGal ] (1 Gal = 0.01 m/s2. i.e. 1 mGal ≈ 10-6 g0 . “Gal” stands for Galileo) - Accuracy unit: [ mGal ].13 instruments
Gravity gradientsGradient of the Earth’s gravity field measured at the satellite orbital height - Physical unit: [ E ] , Eötvös (1 E = 1 mGal / 10 km) - Accuracy unit: [ E ].2 instruments
Magnetic field (scalar)[Unit of measurement – n tesla]13 instruments
Magnetic field (vector) [Unit of measurement - n tesla]19 instruments
* Description adapted from WMO.
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