Cross-correlation-based nuclear magnetic resonance full wave signal noise filtering method

Abstract

The invention relates to a cross-correlation-based nuclear magnetic resonance full wave signal noise filtering method. Based on characteristics that noise is irrelevant to the sinusoidal signals of Larmor frequency but FID amplitude attenuation sinusoidal signals are relevant to the sinusoidal signals of Larmor frequency, the method comprises steps of filtering noise via cross-correlation operation, then fitting envelope of related wave forms, reconstituting correlation wave forms without noise and at last extracting FID signals in nuclear magnetic resonance full wave data by use of the deconvolution algorithm. According to the invention, calculated amount of operation data is small; power frequency, noise of harmonic waves, random noise and peak noise can be simultaneously suppressed; signal to noise ratio of the nuclear magnetic resonance full wave data is remarkably increased, thereby facilitating application range and detection depth of a nuclear magnetic resonance water explorer; additional reference noise eliminating devices are not required, so cost is reduced; and ideal filtering effects of the full wave data which are acquired at a time can be achieved via cross correlation, so measuring time is saved.

Description

technical field [0001] The invention relates to a nuclear magnetic resonance sounding (Magnetic Resonance Sounding, MRS) signal noise filtering method, in particular to a nuclear magnetic resonance full-wave signal noise filtering method based on the principle of cross-correlation noise development. Background technique [0002] The nuclear magnetic resonance groundwater detection uses the artificially excited electromagnetic field to make the hydrogen nuclei in the groundwater form a macroscopic magnetic moment. This macroscopic magnetic moment produces a precession motion in the geomagnetic field. A coil is used to receive the electromagnetic signal generated by the macroscopic magnetic moment precession. The electromagnetic signal The amplitude of the decays exponentially with time and becomes a Free Induction Decay (FID) signal. By analyzing the FID, it is possible to detect whether there is groundwater underground. NMR water finding is a fast and direct method of ground...

AI Technical Summary

Problems solved by technology

When detecting groundwater, the nuclear magnetic resonance signal is very weak, generally at the nV level, while the surrounding electromagnetic field noise is very strong, such as power frequency and its harmonic noise, random noise and spike noise, even if a band-pass filter is used in the signal detection circuit However, the signal-to-noise ratio of the NMR full-wave signal is still very low, generally lower than 0dB, which seriously limits the application of NMR in groundwater detection.

[0005] At present, the NMR full-wave signal generally adopts the data superposition method, which can suppress most of the random noise, but the suppression effect on power frequency noise and spike noise is poor, and the NMR signal needs to be collected multiple times, and the measurement efficiency is low.

CN103823244A discloses a magnetic resonance three-component denoising device, which realizes signal-to-noise separation based on the correlation between the reference channel noise and the noise in the noise-containing signal of the main channel, but due to the irregularity and instability of some noises and The uncertainty of the mixing mechanism limits the application of the algorithm, and adding reference coils and reference channels makes the instrument system large and complex

This invention is mainly aimed at power frequency harmonic interference or a certain single frequency interference in the nuclear magnetic resonance full-wave signal, and cannot filter out random noise and spike noise. The algorithm process of this method is complicated, the calculation amount is large, and the output result is unstable

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