Doppler Navigation for small Aircraft over Sea

The standard aircraft navigation system consists of closely hybridizing an inertial measurement unit (IMU) and a GNSS receiver. GNSS receivers are inexpensive but the signal may be unavailable or unusable, while a low-drift IMU is expensive but provides autonomous navigation. A well-known alternative over land is to merge the measurements from a low-cost IMU with at least three relative groundspeed measurements from a Doppler radar. But this solution gives a biased speed over the sea because its clutter does not provide a zero Doppler reference due to the wind. The paper describes a method to correct this bias by learning a Doppler clutter model offline from a database consisting of a number of significant features extracted from Range-Velocity radar maps.