Altitude integration of radar altimeter and GPS/INS for automatic takeoff and landing of a UAV

An intelligent tilt-rotor UAV is being developed by the Smart UAV Development Center of Korea Aerospace Research Institute. It is equipped with integrated GPS/INS system and RALT(radar altimeter) for automatic takeoff and landing. GPS/INS integration system gives the altitude referenced to WGS-84 ellipsoid which can be vulnerable to external multipath environment. RALT provides the aircraft AGL (above ground level) height with the centimeter level accuracy which is dependent on ground surface characteristics. This paper describes the simple KF (Kalman Filter) setup to integrate altitude information from GPS/INS integration system and RALT with its operational logic. It is evaluated using the data obtained from real flight tests. The result shows proposed method provides highly reliable AGL height for automatic takeoff and landing and compensates GPS/INS derived altitude drift efficiently. The proposed method can be easily applied to the existing system without modifying off-the-shelf GPS/INS integration system. It also has a small computational burden due to its simple model.