GMR combines powerful multi-channel instrumentation with advanced software for precise and economical groundwater investigations. GMR technology delivers direct and non-invasive detection of groundwater and characterization of aquifer properties without drilling expensive wells.
GMR Measurements Provide
- Non-invasive direct detection of groundwater
- Spatial resolution of hydrogeologic parameters in 1D, 2D, or even 3D
- Quantitative determination of water content and porosity
- Estimation of mobile versus bound water content
- Estimation of relative or calibrated hydraulic conductivity and transmissivity
- Investigation to depths up to 150 meters
GMR Applications in Hydrology Include
- Groundwater exploration and well site selection
- Determination of water storage and specific yield
- “Virtual pump testing”: estimation of aquifer properties
- Imaging of preferential flow zones (e.g. fractures, karst conduits, paleochannels)
- Parameterization of groundwater models at local to basin scales
- Integration of logging and surface-based NMR measurements
How GMR Works
GMR detects groundwater using the same physics as a medical MRI scanner, but GMR uses the Earth’s magnetic field in place of the much stronger magnetic field generated inside an MRI magnet. In the geomagnetic field, hydrogen nuclei in groundwater will emit a measurable NMR signal when they are energized at a specific resonant frequency. This NMR signal provides information about the abundance of water and also the size of the pore spaces in which the water resides.
In a GMR survey, the NMR response of groundwater is probed using large wire loops (up to 200 meters on a side), which are laid out on the surface. Short current pulses are routed through one or more of the wire loops to energize the hydrogen nuclei in groundwater at their resonant frequency (1–3 kHz, depending on location). The surface NMR method is also commonly known as magnetic resonance sounding (MRS).
Following the transmit pulse and a short delay, known as the dead-time, the surface loop(s) switch to receive mode and record the NMR signal generated by the energized groundwater. Repeated measurements achieve varied depths of investigation by increasing or decreasing the amount of energy through the surface coils. Advanced signal processing techniques are used to cancel environmental and cultural noise. An advanced, high-resolution linear inversion is implemented to isolate the NMR signals arising from groundwater at different depth locations. Using these isolated NMR signals, the spatial distribution of water content can be directly and quantitatively derived from the signal amplitude. Estimates of key hydrogeologic properties can also be derived, based on the decay time spectrum of the signal.
Top government agencies and research institutes around the world are currently using GMR technology to advance groundwater science.