| Abstract: | A method of non-invasive NMR in the earth's field has been developed and is now used for groundwater surveys to depths of investigation of 100 m or more. A circular wire loop of diameter 100 m, laid out on the ground, is employed to excite and receive the NMR signal in the earth's field. However, in areas with high electromagnetic noise, the NMR measurements may be inaccurate. To overcome this problem, a noise-reducing figure-of-eight-shaped antenna, consisting of two touching coils each of diameter 50 m, has been utilized. Using this antenna, the NMR signal has been calculated for different depths of water-saturated layers with various inclinations of the geomagnetic field. The model calculations and experimental data have been compared and found to be mutually consistent. The two-coil antenna is shown to be suitable for studies at depths of up to 30–40 m, which is of practical importance for engineering geology. |
