The Numis Poly device is a Magnetic Resonance Sounding (MRS) system for the direct detection of shallow groundwater down to 150 m of depth.
• NUMISPoly is a modular multi channel MRS equipment designed with units weighting 25 kg or less, making it man portable.
• The transmitter unit produces pulses at the Larmor frequency • The receiver units (up to 4) measure the MRS signal and the noise, after filtering, amplification and analog to digital conversion.
• The PC computer receives raw data, then processes, displays and stores them (including time series) for further interpretation
• The two DC / DC converter units are required for a maximum investigation depth of 150 m), to energize the 150 m side square loop (600 m total length). However, if an investigation of 100 m is sufficient, one converter unit only is required with a 100 m side square loop (400 m total length) With one only converter, just the transverse time constant (T2*) is measured, while with two converters, the transverse and the longitudinal (T1) time constants are measured; T1 offers a better estimation of the permeability than T2* • The two tuning units must be used at lower magnetic latitudes (for an Earth’s field lower than 31 000 nT with the 150 m side square loop, or 37 000 nT with the 100 m side square loop), while one tuning unit only is needed at medium and higher latitudes
• The receivers 2 to 4 can be used for remote reference purposes (signal to noise enhancement) or 2D acquisition
The MRS method is the only non-invasive method which directly studies groundwater reservoirs from surface measurements:
A pulse of current, at a given frequency is transmitted into a loop. The protons of the groundwater are excited. The signal produced during their return to equilibrium is measured with the same loop. To realize a sounding, different pulse moments (A.ms) are injected in the loop, all corresponding to different investigation depths.
This measure gives access to the soil water content (%) and is related to the mean pore size (permeability).