EXAMPLE 3. PROCESSING GEOTECH AIRBORNE VTEM DATA
FROM ALBERTA (CANADA)
Airborne VTEM surveys were performed by Geotech in Aspen Block area near Fort McMurray, Alberta, Canada (Fig.1), for mapping buried river channels (Eadie et al., 2016) and (Eadie et al., 2016) as potential aquifers.
Near-surface stratigraphy of the area consists of (Fig.2):
- (1) Unconsolidated Quaternary sediments, mostly glacial till and fluvial material, with localized paleovalleys that incise into the underlying formation;
- (2) Grand Rapid Formation, 30 m to 100 m thick, dominated by two sandstone units (50 Ohm*m) separated by a thin muddy sequence (10 Ohm*m), a regional aquiclude;
- (3) Clearwater Formation, a uniform marine shale unit, 60 m to 90 m thick (<10 Ohm*m);
- (4) McMurray Formation that mostly consists of fluvial sandstones and in some regions containing important reservoirs of oil and water sands (500-1000 Ohm*).
Surveys aimed at mapping buried aquifers appearing as resistive lineaments. TEM responses were measured by a VTEM system, in a central-loop configuration, consisting of a receiver loop, 3 m in diameter, placed in the center of a transmitter with 4 turns, 26 m in diameter, transmitter current 256 A.
Aquifers in resulting resistivity-depth sections are marked by high resistivity.
See below video tutorial for processing VTEM data in TDEM Geomodel.
During VTEM data processing, transmitter and receiver parameters are loaded as MCG file, which also stores the source waveform (any arbitrary form is possible). Airborne surveys differ from land-based measurements in using radarb parameter that refers to fly height. This parameter is loaded into TDEM Geomodel, together with transients, as a .XYZ file, a dump file of Geosoft database.
The tab Google maps is inactive because field data are loaded to TDEM Geomodel in relative coordinates.