Method of calibrating a heading reference system
A method of calibrating a vehicle's heading system, such as the attitude heading and reference system of an aircraft or the heading system of a ship, positioned along the Earth's surface involves obtaining both actual and theoretical readings for the magnetometer of the heading system, and comparing these values to obtain calibration values for the heading system which are then averaged to obtain a universal average gain and offset for the magnetometer. The vehicle may be repositioned, such as to North, South, East, and west magnetic headings, with the procedure repeated at each of these headings, and the calibration values averaged, further increasing the accuracy.
1. A method for calibrating an aircraft attitude and reference heading system comprising at least one magnetometer, the method comprising the steps of:
selectively positioning an aircraft on the ground along the Earth's surface;
obtaining an actual reading from the at least one magnetometer at a selected magnetic heading for the positioned aircraft while the aircraft is stationary on the ground;
obtaining a set of theoretical magnetic field properties of the Earth at a location of the positioned aircraft, the obtained theoretical magnetic field properties comprising theoretical values for a horizontal intensity and a vertical intensity of the magnetic field at the location of the positioned aircraft;
computing a theoretical reading for the at least one magnetometer at the selected magnetic heading of the positioned aircraft based on at least the magnetic heading, the associated attitude for the positioned aircraft, and the obtained theoretical values for the magnetic field at the location of the positioned aircraft;
comparing the obtained actual reading from the at least one magnetometer for the positioned aircraft at the magnetic heading with the obtained theoretical magnetometer reading at the magnetic heading for providing a calibration value for the heading system at the magnetic heading for the positioned aircraft;
utilizing the provided calibration value at the magnetic heading of the aircraft to calculate a universal average gain and offset for the at least one magnetometer; and
utilizing the universal average gain and offset to universally calibrate the heading system with respect to measurement errors.
2. The method of claim 1 wherein the selected magnetic heading for the aircraft the is selected from the group consisting of North, South, East, and West magnetic headings for the aircraft.
3. The method of claim 1 wherein the at least one magnetometer comprises a triaxial magnetometer.
4. The method of claim 1 wherein the step of obtaining the set of theoretical magnetic field properties further comprises obtaining the set from an organization that provides access to geophysical data.
5. The method of claim 1 wherein the aircraft has an associated engine and avionics, the calibration method being performed with the aircraft engine and avionics running.
6. The method of claim 1 wherein the at least one magnetometer comprises a triaxial magnetometer and the equation for the aircraft magnetic heading is:
ψ
=
-
tan
-
1
(
Y
θ
X
θ
)
Where:
Y θ =yMag cos φ− zMag sin φ
X θ =xMag cos θ+ yMag sin θ sin φ+ zMag sin θ cos φ.
7. A method for calibrating a heading system for a vehicle comprising at least one magnetometer, the method comprising the steps of:
selectively positioning the vehicle along the Earth's surface;
obtaining an actual reading from the at least one magnetometer at a selected first magnetic heading for the positioned vehicle while the vehicle is stationary on the Earth's surface;
obtaining a set of theoretical magnetic field properties of the Earth at a location of the positioned vehicle, the obtained theoretical magnetic field properties comprising theoretical values for a horizontal intensity and a vertical intensity of the magnetic field at the location of the positioned vehicle;
computing a theoretical reading for the magnetometer at the selected magnetic heading of the positioned vehicle based on at least the magnetic heading, and the obtained theoretical values for the magnetic field at the location of the positioned vehicle;
comparing the obtained actual reading from the at least one magnetometer for the positioned vehicle at the selected magnetic heading with the obtained theoretical magnetometer reading at the first magnetic heading for providing a first calibration value for the heading system at the selected magnetic heading for the positioned vehicle;
utilizing the provided calibration value at the magnetic heading of the vehicle to calculate a universal average gain and offset for the at least one magnetometer; and
utilizing the universal average gain and offset to universally calibrate the heading system with respect to measurement errors.
8. The method of claim 7 wherein the vehicle is a ship positioned in water along the Earth's surface.
9. The method of claim 7 wherein the selected magnetic heading for the vehicle is selected from the group consisting of North, South, East, and West magnetic headings for the aircraft.