Model GMR - Multi-Channel Instrumentation
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
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.
At the core of the GMR’s design are Vista Clara’s patented multi-channel instrumentation, acquisition, and processing techniques**. The GMR system provides the most complete and robust multi-channel capabilities: the ability to transmit and receive on any surface coil or combination of surface coils. The patented mutli-channel approach provides key advantages for rapid surface NMR surveys, imaging in 2D or 3D, and noise cancellation, which is a necessity for measurements near power lines or other noise sources.
Advanced Noise Cancellation
GMR instrumentation and software includes powerful noise cancellation that leverages our proprietary multi-channel data acquisition design **. This critical advantage allows a GMR user to produce high quality surface NMR data and inversion results in locations where other instruments fail detect groundwater signals.
2D/3D Groundwater Imaging (Magnetic Resonance Tomography):
Vista Clara pioneered the development and use of 2D/3D surface NMR imaging using multiple surface coils. GMR’s multi-channel data acquisition and software make 2D imaging fast and precise. Direct 2D NMR imaging is especially useful for detecting and imaging structures such as karst conduits, paleochannels, and other highly localized hydrological features. GMR’s patented high-impedance ultralow-noise receivers‡ are designed to prevent mutual coupling, which is essential for accurate 2D or 3D surface NMR imaging.
Sophisticated Hydrological Analysis Software:
GMR includes the most advanced commercial software for 1D magnetic resonance soundings, inversions, and hydraulic parameter estimation. The GMR 1D inversion software package includes:
- Our patented low-SNR permeability indicator**, as well as other empirical formulas for estimating relative and calibrated hydraulic conductivity.
- Our proprietary all-linear 1D inversion code with 3D source modeling
- Multi-exponential analysis software, to estimate the distribution of water content versus T2* decay time. This feature is required to estimate the pore size distribution and to distinguish bound versus mobile water content.
- Estimation of T1 and T2 decay times from double-pulse and spin-echo measurements.
Short Instrument Dead-time:
Water bound in silts and clays or water in iron-rich formation (e.g., basalts, magnetite-rich sands) typically exhibits very short decay times (
The GMR hardware and acquisition software employs sophisticated measurements in which two energizing pulse are transmitted in rapid succession through the surface coils. These double-pulse measurements allow T1/recovery and T2/spin-echo measurements which can yield more robust estimates of hydrogeologic properties and are required for surveys in environments with magnetic geology. The use of phase cycling suppresses measurement artifacts leading to improved data quality