Method and device for compensating vertical magnetic defaults of a magnetometer installed in an aircraft

A method for compensating vertical magnetic anomalies of a magnetometer used for piloting an aircraft, the magnetometer being associated with a reference coordinate frame XM, YM, ZM thereof and the aircraft being associated with an aircraft coordinate frame XA, YA, ZA thereof, the method, as implemented by a processor of a programmable electronic device, comprising:

• a first step of obtaining first values of compensation coefficients for magnetic anomalies of a magnetometer installed in the aircraft, the compensation coefficients corresponding to the Euler angles associated with a rotation which changes from the reference coordinate frame of the magnetometer to the aircraft coordinate frame, and
• a second step including an estimation of at least one compensation coefficient for vertical magnetic anomalies of the magnetometer, implemented during flight of the aircraft, the second step comprising:
• a) an acquisition of a plurality of values for magnetic field vectors, as measured the in-flight by the magnetometer and values of in-flight attitude angles of the aircraft,
• b) a calculation of a magnetic heading as a function of the first values of compensation coefficients from the first step and the acquired values for magnetic field vector,
• c) a recursive calculation of a slope coefficient, as a function of a difference in heading between the calculated magnetic heading and a reference magnetic heading, and values of the aircraft attitude angles, and
• d) a calculation of a value of the compensation coefficient for vertical magnetic anomalies, using a vertical bias estimator, using the calculated slope coefficient, the aircraft attitude angle values and characterizing values of a local terrestrial magnetic field;
• the method further comprising applying said compensation coefficient for vertical magnetic anomalies to compensate vertical magnetic anomalies of the magnetometer and to harmonize alignment of the magnetometer with respect to the aircraft coordinate frame, and updating a value of a compensated vertical component of the magnetic field, as a function of the calculated value of the compensation coefficient for vertical magnetic anomalies.