High-precision frequency measurement approach of diminishing multi-source errors for UAV-based aeromagnetic survey

Compared with crewed aircraft, the optically pumped sensor on the aeromagnetic UAV is closer to the electromagnetic interference sources, significantly affecting the frequency measurement of the sensor. A high-precision frequency measurement approach of diminishing multi-source errors for UAV aeromagnetic surveys is proposed to address this unique issue. The quantization error from counting the reference signal is significantly mitigated using multiple phase-shifted clocks, and the negative effect of trigger error is weakened using Tukey robust regression-based frequency estimation method. We also developed a dedicated aeromagnetic acquisition instrument and a test platform. The results indicate that the frequency resolution of the proposed method can reach 0.001 Hz at 70–350 kHz (10-Hz sampling rate) and the magnetic sensitivity is as low as 0.56 pT/Hz@1 Hz. The fourth-order difference magnetic noise on the UAV helicopter is significantly reduced from 0.0321 nT for the existing multi-channel method to 0.0045 nT for the proposed method.