Satellite geodesy

Satellite geodesy uses satellite observations to determine Earth’s shape, gravity field, rotation, and changing surface positions.

Global Navigation Satellite System: A satellite-based system that provides positioning and timing through signals transmitted by orbiting spacecraft. Continuous GNSS positioning tracks station coordinates and their motion relative to Earth.
Geodesy: The science of measuring Earth’s shape, orientation, gravity field, and changing positions. Satellite geodesy is the space-based branch of this broader measurement science.
Plate tectonics: The theory that Earth’s lithosphere consists of moving plates interacting at their boundaries. Long GNSS time series measure plate velocities and test models of tectonic motion.
LAGEOS: A pair of passive, laser-ranged satellites used for geodetic measurements of Earth. Their long, stable orbits support precise measurements of Earth rotation, gravity, and tectonic motion.
Spirit leveling: A surveying method that determines height differences by measuring horizontal sight lines between graduated staffs. Unlike satellite positioning, it measures local height differences directly along surveyed routes.
Satellite laser ranging: A technique that measures distance to satellites by timing laser pulses reflected from them. Laser ranges to geodetic satellites constrain Earth’s center of mass and gravity field.
Geodetic datum: A reference framework that defines coordinates and their relationship to Earth. Satellite positions become meaningful only when tied to a defined terrestrial reference.
Earthquake geodesy: The measurement of ground deformation associated with earthquakes using geodetic observations. Satellite positioning and radar interferometry map coseismic displacement over broad areas.
TOPEX/Poseidon: A joint NASA–CNES satellite mission that measured global ocean-surface topography from 1992 to 2006. Its precision radar altimetry established a continuous record of global sea-level change.
Satellite altimetry: The measurement of surface height from a satellite using the travel time of transmitted pulses. It is a focused geodetic method for measuring ocean and land elevation from orbit.

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