Global Positioning System (GPS).

A navigation sensor based on satellites; A Global Positioning System (GPS) provides highly accurate navigation data: position, velocity, and time reference. GPS is often aided by the INU, AHRS, and Doppler data. GPS is accurate with four or more properly oriented satellites. Accuracy is degraded with improperly placed satellites or fewer than four satellites visible. GPS-INS is the most accurate of modes listed, with day/night and all weather capability.