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

Abstract

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.