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.

中文翻译：

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频域数据采集与多帧谱相减相结合的磁共振测深电磁噪声抑制

作为一种先进的地下水探测方法，磁共振波探（MRS）已受到越来越多的关注。但是，最大的挑战是MRS测量始终遭受不良的信噪比（SNR）。针对MRS测量中的噪声干扰问题，我们提出了一种基于数据采集和多帧频谱减法（DA-MFSS）相结合的新型噪声抑制方法。来自测量区域的纯净环境噪声首先被接收线圈收集，然后在脉冲矩传输之后记录有噪声的MRS信号。纯噪声和有噪声的MRS信号采集的过程将重复几次。然后，将纯噪声和噪声信号求平均以初步抑制噪声。其次，平均的纯噪声和噪声信号被分成多个帧。帧信号被变换到频域中，并且应用频谱减法来进一步抑制嵌入在有噪声的MRS信号中的电磁噪声。最后，通过重叠相加法和傅立叶逆变换来恢复去噪信号。通过数值模拟和现场测量对方法进行了检验。应用所提出的方法后，MRS数据的信噪比提高了16.89 dB，随机噪声和谐波噪声均得到了很好的抑制。通过重叠相加法和傅立叶逆变换来恢复降噪后的信号。通过数值模拟和现场测量对方法进行了检验。应用该方法后，MRS数据的信噪比提高了16.89 dB，随机噪声和谐波噪声均得到了很好的抑制。通过重叠相加法和傅立叶逆变换来恢复降噪后的信号。通过数值模拟和现场测量对方法进行了检验。应用所提出的方法后，MRS数据的信噪比提高了16.89 dB，随机噪声和谐波噪声均得到了很好的抑制。