12
Twisted Oak Street Brampton, Ontario L6R1T1 Tel: (905) 458-1883
ClearView
Geophysics Inc. specializes in the application of ground-based geophysical surveys
for environmental, geotechnical and mineral exploration. Our business is centred
on the ability to operate various geophysical instruments in sometimes rugged
and difficult field conditions. The acquired data are subsequently processed/plotted
and interpreted to guide follow-up intrusive investigations.
Two
instruments demonstrated: Geonics EM31 Ground Conductivity Meter and Scintrex
EnviC Cesium Magnetometer.
The Geonics
EM31 Ground Conductivity Meter is built and serviced by Geonics Limited based
in Mississauga, Ontario. It a one-person operated instrument that has two poles
extending from the control box. The total length is approximately 4 metres long.
The data recorded are apparent conductivity (quadrature) and in-phase. The instrument
can be run in the standard vertical dipoles mode which has a penetration depth
of approximately 6 metres with most of the response coming from below ~2 metres.
The less commonly used horizontal dipoles mode has a penetration depth of approximately
3 metres with most of the response coming from near surface. The apparent conductivity
and inphase components are plotted as separate maps that can be post-processed
to accentuate subtle features caused by former foundations, pipes/utilities, limits
of fill, contaminant plumes, settling pond leaks and so forth. The inphase component
is more sensitive to metal and therefore is useful for detecting buried metal.
An experienced geophysicist can often interpret the source based on the character
of the coincident apparent conductivity and inphase response. ClearView carries
out EM31 surveys in streaming 10x/second mode by combining the system with a DAP
logger and AgGPS132 receiver. This allows for rapid positioning, plotting and
interpretation while still in the field.
The Scintrex EnviC Cesium Magnetometer
is a relatively new instrument introduced last year by Scintrex of Concord,
Ontario. It is a follow-up system to the NavMag cesium magnetometer. The system
is run using a DAP logger (a Quebec based company) running navigation and acquisition
software written by Scintrex. The cesium sensor is one of the fastest magnetic
sensors commercially available. It is standard for airborne geophysical surveys.
ClearView routinely uses cesium magnetometers for snowmobile-mode and walking-mode
surveys in the arctic, where diurnal variations and magnetic gradients can be
very high. ClearView uses GEM Systems Overhauser magnetometers as base stations.
All systems are synchronized to UTC time. Cesium magnetometers are excellent for
detecting buried metal, with or without a base station. The base station is necessary
to remove diurnal variations caused by solar activity so that subtle buried objects
and structures can be more accurately detected and mapped.
We will
demonstrate how these two instruments are applied in the field and display data
that was collected that morning from the demonstration site .
