Which system uses satellites to determine the exact location of a device?

• A. Doppler
• B. Inertial Navigation System
• C. Global Positioning System (GPS)
• D. Galileo

Answer: (C)

Positioning with satellites relies on measuring how far you are from orbiting satellites and solving for your exact location. The Global Positioning System achieves this by receiving signals from multiple satellites that carry precise time stamps. The receiver compares its own time to those stamps, converts the signal travel time into distance to each satellite, and then uses those distances to determine your exact position in three dimensions plus correct for the receiver’s clock error. You need several satellites to solve for all unknowns, typically at least four.

Doppler, by contrast, measures frequency shifts to infer velocity rather than absolute position. An inertial navigation system uses on-board sensors like accelerometers and gyroscopes to estimate movement but drifts over time without external references. Galileo is another satellite navigation system that can provide similar positioning, but GPS is the well-known system described when pinpointing location using satellites.