Electromagnetic Noise Suppression of Magnetic Resonance Sounding Combined with Data Acquisition and Multi-Frame Spectral Subtraction in the Frequency Domain

Tingting Lin,Xiaokang Yao,Sijia Yu,Yang Zhang

doi:10.3390/electronics9081254

Abstract

As an advanced groundwater detection method, magnetic resonance sounding (MRS) has received more and more attention. However, the biggest challenge is that MRS measurements always suffer with a bad signal-to-noise ratio (SNR). Aiming at the problem of noise interference in MRS measurement, we propose a novel noise-suppression approach based on the combination of data acquisition and multi-frame spectral subtraction (DA-MFSS). The pure ambient noise from the measurement area is first collected by the receiving coil, and then the noisy MRS signal is recorded following the pulse moments transmitting. The procedure of the pure noise and the noisy MRS signal acquisition will be repeated several times. Then, the pure noise and the noisy signal are averaged to preliminarily suppress the noise. Secondly, the averaged pure noise and the noisy signal are divided into multiple frames. The framed signal is transformed into the frequency domain and the spectral subtraction method is applied to further suppress the electromagnetic noise embedded in the noisy MRS signal. Finally, the de-noised signal is recovered by the overlap-add method and inverse Fourier transformation. The approach was examined by numerical simulation and field measurements. After applying the proposed approach, the SNR of the MRS data was improved by 16.89 dB and both the random noise and the harmonic noise were well suppressed.

Highlights

Magnetic resonance sounding (MRS) is a direct and nondestructive method in underground water detection
After applying the proposed approach, the signal-to-noise ratio (SNR) of the magnetic resonance sounding (MRS) data was improved by 16.89 dB and both the random noise and the harmonic noise were well suppressed
This paper proposes another de-noising method, which combines data acquisition and multi-frame spectral subtraction (DA-MFSS)

Summary

Introduction

Magnetic resonance sounding (MRS) is a direct and nondestructive method in underground water detection. It provides water content distribution and estimates hydrogeological properties and has been widely applied in hydrogeological investigation [1,2,3]. The low signal-to-noise ratio (SNR) is always the main reason to restrict the application of this method [4,5]. The weak signal, which is only tens to thousands of nano-volts, is difficult to be detect. The relaxation time of MRS signal is relatively short, i.e., a few hundred milliseconds, which requires higher sensitivity of the MRS receiver [6,7]. Obtaining the reliable MRS signal has become a key point in MRS measurement

Methods

Discussion

Conclusion