Extended spectrum modulation method for MTEM harmonic noise filtering

Abstract

Harmonic noise represented by power-line noise is the main interference of Multi-transient electromagnetic (MTEM), and traditional filtering methods inevitably suffer from noise residue and waveform distortion. The key step in MTEM is the extraction of the earth impulse response, which is equivalent to filtering the voltage response signal using an identification system. This paper modulates the spectrum of the identification system by extending the source signal to increase the attenuation at these target frequencies in order to filter out harmonic noise when extracting the earth impulse response, which we named as Extended Spectrum Modulation Method (ESMM). This paper first deduces the mathematical relationship between data length and target frequency. The filtering of power-line harmonics by ESMM is then demonstrated and compared with a conventional notch filter. This paper also proposes a rapid deployment method for ESMM to improve data utilization. Since ESMM filters out noise while extracting the earth impulse response, there is no additional hardware cost or time overhead. Finally, a field experiment demonstrates the superior performance and ultimate convenience of ESMM.