Real-time compensation of magnetic data acquired by a single-rotor unmanned aircraft system

Two methods for low-altitude calibration of a single-rotor unmanned aircraft system using a real-time compensator are tested: (1) a stationary calibration where the unmanned aircraft system executes manoeuvres while hovering in order to minimize ambient field changes due to the local geology; and (2) an adapted box calibration flown in four orthogonal directions. Both methods use two compensator-specific limits derived from established methods for manned airborne calibration: the lowest frequency used by the compensator for the calibration algorithm and the maximum variation of the ambient magnetic intensity experienced by the unmanned aircraft system during calibration. Prior to flying, the unmanned aircraft system was magnetically characterized using the heading error and fourth difference. Magnetic interference was mitigated by extending the magnetometer-unmanned aircraft system separation distance to 1.7 m, shielding, and demagnetization. The stationary calibration yielded an improvement ratio of 8.595 and a standard deviation of the compensated total magnetic intensity of 0.075 nT (estimated Figure-of-Merit of 3.8 nT). The box calibration also yielded an improvement ratio of 3.989 and a standard deviation of the compensated total magnetic intensity of 0.083 nT (estimated Figure-of-Merit of 4.2 nT). The stationary and box calibration solutions were robust with low cross-correlation indexes (1.090 and 1.048, respectively) when applied to a non-native data set.