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How does GPS use radio signal travel time to measure distance from a satellite?

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Cruise ship captain in uniform studies navigational charts with a compass on a table in the ship's bridge. — navigation Officers on a passenger ship using charts for navigation.

GPS satellites utilize highly accurate atomic clocks to transmit precise time signals to receivers on Earth. To determine the distance from a satellite, a receiver calculates the time elapsed between the signal's transmission and its arrival.12

Because radio signals travel at the speed of light—approximately 300,000 kilometers (186,000 miles) per second—the receiver multiplies this speed by the travel time to find the distance. This distance establishes that the receiver is located somewhere on the surface of an imaginary sphere with a radius equal to that distance. By processing signals from at least four satellites, the receiver’s computer identifies the point where these spheres intersect, allowing it to calculate precise longitude, latitude, and altitude.12