Inertial Navigation System (INS)

An Inertial Navigation System (INS) is a self-contained dead-reckoning device that computes position, velocity, and attitude from accelerometers and gyroscopes alone, without any outside signal. Three accelerometers measure specific force and three gyros measure angular rate; the system integrates acceleration once for velocity and again for position, starting from a known fix and heading. Because it integrates, small sensor errors accumulate as drift that grows with time, so a marine INS is aided by GNSS, the speed log, and the gyrocompass to bound the error. Its value is immunity to jamming and spoofing: when GNSS is denied, the INS carries the ship through the gap.