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How does satellite trilateration help determine precise locations on Earth’s surface?

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Diagram showing the deflection of the vertical from the geoid to the ellipsoid or spheroid, with labeled lines for geoid, spheroid, rock surface, ocean, and geoid height in a geology context. — geoid Deflection of the vertical from the geoid to the spheroid.

Satellite trilateration is a precise method used to determine locations on Earth by measuring the distance between a receiver and multiple satellites. Because the exact position of these satellites is known at any given time, the process functions as follows:

Distance Measurement: A receiver calculates the time it takes for a satellite signal to reach it. By multiplying this time by the speed of radio waves, the receiver determines its distance from the satellite.1
Spherical Intersection: This distance places the receiver on the surface of an imaginary sphere centered on the satellite. By processing signals from at least four satellites, the receiver’s computer calculates the point where these spheres intersect, providing precise longitude, latitude, and altitude.1

In the context of geodesy, this technique is vital for mapping the geoid. While satellite trilateration provides geometric coordinates, scientists also use satellite tracking and radar altimetry to study Earth's gravitational field and shape. By simultaneously determining station coordinates and orbital parameters, researchers can refine models of the geoid, which serves as the essential reference surface for measuring elevations across the planet.23