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TitleIncorporating ancillary data into the inversion of airborne time-domain electromagnetic data for hydrogeological applications
AuthorSapia, V; Oldenborger, G A; Viezzoli, A; Marchetti, M
SourceJournal of Applied Geophysics vol. 104, 2014 p. 35-43,
Alt SeriesEarth Sciences Sector, Contribution Series 20130299
Mediapaper; on-line; digital
File formatpdf
NTS62F; 62G; 62J; 62K
Lat/Long WENS-102.0000 -98.0000 51.0000 49.0000
Subjectsgeophysics; hydrogeology; electromagnetic mapping; electromagnetic fields; e m surveys; Spiritwood aquifer
Illustrationsprofiles; plots
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
AbstractHelicopter time-domain electromagnetic (HTEM) surveys often suffer from significant inaccuracies in the early-time or near-surface data - a problem that can lead to errors in the inverse model or limited near-surface resolution in the event that early time gates are removed. We present an example illustrating the use of seismic data to constrain the model recovered from an HTEM survey over the Spiritwood buried valley aquifer in Manitoba, Canada. The incorporation of seismic reflection surfaces results in improved near-surface resistivity in addition to a more continuous bedrock interface with a sharper contact. The seismic constraints reduce uncertainty in the resistivity values of the overlying layers, although no a priori information is added directly to those layers. Subsequently, we use electrical resistivity tomography (ERT) and borehole data to verify the constrained HTEM models. Treating the ERT and borehole logs as reference information, we perform an iterative time-shift calibration of the HTEM soundings to achieve regional-scale consistency between the recovered HTEM models and the reference information. Given the relatively small time-shifts employed, this calibration procedure most significantly affects the early-time data and brings the first useable time gate to a time earlier than the nominal first gate after ramp off. Although time shifts are small, changes in the model are observed from the near-surface to depths of 100 m. Calibration is combined with seismic constraints to achieve a model with the greatest level of consistency between data sets and, thus, the greatest degree of confidence. For the Spiritwood buried valley, calibrated and constrained models reveal more structure in the valley-fill sediments and increased continuity of the bedrock contact.
Summary(Plain Language Summary, not published)
Airborne geophysical data can be used for efficient regional aquifer mapping. However, models resulting from geophysical data can suffer from limited resolution and unknown degrees of uncertainty - problems that can lead inconsistencies with other data sets and difficulty in building unique hydrogeological models. We use a helicopter time-domain electromagnetic survey over the Spiritwood valley aquifer in Manitoba, Canada to demonstrate a methodology for incorporating multiple geophysical and borehole data types into a single analysis procedure. The result is a model that is consistent with multiple datasets and that has a much higher level of confidence.