A Robust Denoising Method Based on Coherent Signal Enhancement Method and Whitening Filter for Shaft-Rate Electromagnetic Field

Traditional magnetic anomaly detection struggles to accurately detect underwater targets at long distances. Ships generate a shaft-rate electromagnetic (EM) field at the propeller rotation frequency as the fundamental frequency when sailing, providing a novel method for underwater target detection. However, the majority of conventional denoising techniques are inadequate for colored noise. Additionally, a distinct interference line spectrum exists within the shallow-sea background EM field or measurement device detection errors, exhibiting characteristics in the frequency domain that closely resemble the shaft-rate EM field. These noises which significantly elevating the false alarm rate in shaft-rate EM field detection. This research presents a denoising method R-CSEM-WF, which integrates a robust coherent signal enhancement approach (R-CSEM) with an enhanced whitening filter (WF). It further enhances the framework of the differential method, allowing it to separate the target signal in conditions of exceedingly low signal-to-noise ratios (SNRs). A fusion method is proposed to suppress errors caused by axial differences or time delays between sensors. Furthermore, the enhanced whitening filter reallocates remaining low-frequency noise to the higher frequency band, therefore amplifying the octave components in the target signal. Test results on both simulated and empirical data demonstrate that our method can efficiently mitigate interference line spectrum and colored noise, while augmenting the features of shaft-rate EM field.