Multi-channel Design

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 Short Signal with Noise Cancellation

Field GMR data showing raw signal (blue), contaminated by noise, and resulting groundwater FID signal following noise cancellation (red).

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 to detect groundwater signals.

2D/3D Groundwater Imaging (Magnetic Resonance Tomography):

Scientific Infographic

2D GMR image of a limestone aquifer near San Antonio Texas. A probable water-filled cave or fracture system is shown at the right of the image. The investigation also identified a limestone formation with lower permeability delineated at the left edge of this image.

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
vertical line graphs

GMR advanced 1D inversion of data from Nebraska, USA, with low-SNR permeability indicator shown at far left.

Graphs comparing data

Data from the same site processed via multi-exponential analysis illuminating the complex nature of the aquifer. Signals with short decay times (towards left of image) indicate water in small pores of low permeability silt and clay. Signals with long decay times (towards right of image) indicate water in productive aquifers, in this case sands, gravels and sandstones.

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 (<20 ms).  The uniquely short dead-time of the GMR instrument (4 ms preprocessed) makes it possible to detect and characterize these very short signals, which otherwise could not be observed.  GMR thus provides detection of groundwater in the widest range of environments, enabling direct imaging of aquicludes and confining units as well as more accurate estimation of hydrogeologic properties.

Double-Pulse Measurements:

Chart of Scientific Data

NMR signals from groundwater in an aquifer with magnetic mineralogy. The FID signal (in black) from a single pulse measurement decays with a very short T2* rate (200ms) revealing that the aquifer actually has high permeability. Phase cycling in the double-pulse sequence used to measure spin echoes supresses artifacts and improves data quality.

The GMR hardware and acquisition software employs sophisticated measurements in which two energizing pulses 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.