Esben Auken

Surface nuclear magnetic resonance (NMR) holds a special place among the tools used for hydrogeophysical measurements as it provides a direct depth-resolved measurement of the water volume in the shallow surface. Further, the NMR data also provides information on the pore-space properties of the subsurface, which informs about hydraulic properties. The method has been successfully applied in many scenarios, but it is still challenged by e.g. low production rates and low signal-to-noise ratios in many places of interest. In an effort to address these challenges, we present a new surface NMR instrument named Apsu. The instrument is designed modularly, and it consists of a transmitter system, a wirelessly connected receiver system using small coils, and a control system. The transmitter is powered by a generator and drives an un-tuned transmit coil with a peak current of 105 A. The frequency and amplitude of each half-oscillation of the transmit pulse are independently controlled giving full flexibility in NMR pulse design. The system has a quasi-zero dead time and a 30 m depth of investigation. The system performance is verified with field example.