Which statement describes a multipath error in GPS measurements?

• A. It occurs when signals reflect off surfaces before reaching the receiver.
• B. It only affects the satellite clock.
• C. It is the result of an atmospheric disturbance.
• D. It reduces receiver noise to negligible levels.

Answer: (A)

Multipath error happens when GPS signals take more than one path to reach the receiver, typically one direct path and one reflected path from surfaces like buildings, water, or the ground. The receiver assumes the signal came straight from the satellite, so the reflected signal alters the apparent travel distance, biasing the measured range. This ground- or near-surface reflection mainly degrades the code (pseudorange) measurements, and can also affect carrier measurements to a lesser extent. It is not caused by the satellite clock or atmospheric disturbances, and it does not reduce receiver noise; it adds an error due to the mixed paths.