Inertial Navigation System (INS).

An Inertial Navigation System (INS) is a self-contained navigation system. It consists of gyroscopes and accelerometers to provide attitude, heading, position, attitude, body/inertial velocity, and acceleration information. A primary navigation data source. INS loses accuracy with time due to drift of gyroscopes. INS-DNS is moderately accurate over land, not good over water. See Also: Inertial Navigation Unit;