Pulsed Nuclear Magnetic Resonance Instrument for Soil‐water Content Measurement: Sensor Configurations

Abstract Two sensor configurations of a prototype soil‐water content measuring instrument were examined. The prototype instrument, based on pulsed nuclear magnetic resonance technology, is designed for field use and is capable of determining volumetric soil‐water content at depths of 38, 51, and 63 mm. The magnet component of the sensor is modified by the use of pole pieces so that the sensor is capable of operating in two configurations, flat and extended. In the flat configuration, the sensor rides or floats directly on the soil surface, whereas in the extended configuration, two furrows about 10‐cm deep are created in the soil to accommodate the extended pole pieces. Test results show that the instrument is more sensitive to volumetric soil‐water content with the sensor in the extended configuration as opposed to the flat configuration. Furthermore, sensitivity decreases with increasing measurement depth. Sensitivity differences are explained in terms of magnetic field and radio‐frequency signal characteristics.