The surface nuclear magnetic resonance (SNMR) method is widely used in groundwater detection because of its sensitivity to hydrogen in water and direct water detection. However, low signal‐to‐noise ratios (SNRs) restrict the development of this technique. An optimum pulse sequence is designed according to correspondence between the pulse moment strength and its best detection depth. Because only selection of the pulse intensity distribution according to the target aquifer depth is required and the “on‐resonance” pulse pattern is still employed, this pulse sequence emission can be easily achieved using existing SNMR instrumentation. Numerical simulation results and field experiments show that, compared with traditional exponential growth pulses, the optimum pulse sequence effectively improves the SNR of the SNMR method. The aquifer boundary, water content, and pore characteristics of the inversion result are thus more consistent with characteristics of underground structures. Additionally, because the optimum pulse sequence focuses most of the pulse moments in the target depth range, in situations where two aquifers are separated by a relatively narrow aquitard, it is better able to resolve the individual aquifers than the traditional pulses. Optimum pulse moments improve the SNR by enhancing the signal amplitude, compared with various filtering methods, and obtain a better detection effect. This kind of pulse sequence can be used as an alternative pulse sequence form of the SNMR method.

中文翻译：

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最佳脉冲矩在表面核磁共振中的优势及其在地下水勘探中的应用

表面核磁共振（SNMR）方法由于对水中氢和直接水的检测灵敏度高，因此在地下水检测中被广泛使用。但是，低信噪比（SNR）限制了该技术的发展。根据脉冲力矩强度与其最佳检测深度之间的对应关系，设计出最佳脉冲序列。由于仅需要根据目标含水层深度选择脉冲强度分布，并且仍采用“共振”脉冲模式，因此可以使用现有的SNMR仪器轻松实现此脉冲序列发射。数值模拟结果和现场实验表明，与传统的指数增长脉冲相比，最优脉冲序列有效地提高了SNMR方法的信噪比。含水层边界，因此，反演结果的含水量和孔隙特征与地下结构的特征更加一致。此外，由于最佳脉冲序列将大多数脉冲矩聚焦在目标深度范围内，因此在两个含水层被相对较窄的脱水层隔开的情况下，与传统脉冲相比，它能够更好地解析单个含水层。与各种滤波方法相比，最佳脉冲矩可通过增强信号幅度来改善SNR，并获得更好的检测效果。这种脉冲序列可以用作SNMR方法的替代脉冲序列形式。因为最佳脉冲序列将大多数脉冲矩聚焦在目标深度范围内，所以在两个含水层被相对较窄的含水层分开的情况下，与传统脉冲相比，解析单个含水层的能力更好。与各种滤波方法相比，最佳脉冲矩可通过增强信号幅度来改善SNR，并获得更好的检测效果。这种脉冲序列可以用作SNMR方法的替代脉冲序列形式。因为最佳脉冲序列将大多数脉冲矩聚焦在目标深度范围内，所以在两个含水层被相对较窄的含水层分开的情况下，与传统脉冲相比，解析单个含水层的能力更好。与各种滤波方法相比，最佳脉冲矩可通过增强信号幅度来改善SNR，并获得更好的检测效果。这种脉冲序列可以用作SNMR方法的替代脉冲序列形式。