The advantages of repeating survey lines during FDEM data collection for high resolution subsurface mapping
Abstract
Frequency domain electromagnetic (FDEM) data are commonly acquired to provide spatially continuous and detailed information about electric and magnetic properties. Hereby FDEM instrument typically employ symmetrical (e.g. horizontal coplanar, HCP) or asymmetrical (e.g. perpendicular, PRP) coil configurations, with respect to survey heading. While the former render an isotropic response, which is therefore unaffected by the acquisition direction, an asymmetrical configuration will produce different responses based on survey heading.
Collecting spatially exhaustive FDEM survey data is performed in a systematic spatial pattern. Often bidirectional or snakeline survey patterns are used, with adjacent survey lines being parallel and facing opposing directions, as these are highly time efficient as opposed to unidirectional survey patterns. However, these patterns result in reduced discrimination potential of subsurface structures by the introduction of staggering or fishbone patterns. These relate to (a combination of) several factors: (1) a time lag, which is present for both asymmetrical and symmetrical configurations, or georeferencing errors, and (2) the effect of survey heading, which is inherently connected to the asymmetrical nature of the FDEM configurations. We propose a bidirectional and time-efficient survey style, where (random) survey lines are repeated (and therefore overlapping), which offers multiple advantages. Accurate estimates of the time lag, or georeferencing errors can be made. Issues related to asymmetrical staggering can be tackled through a data-driven approach using Bayesian ridge regression to transform the collected (snakeline) data to unidirectional data. As such, accurately georeferenced FDEM datasets at high resolution are available for interpretation in both acquisition directions, providing more flexibility to customize survey design to the subsurface targets and field survey conditions.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNS42A..13H
- Keywords:
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- 0915 Downhole methods;
- EXPLORATION GEOPHYSICS;
- 0925 Magnetic and electrical methods;
- EXPLORATION GEOPHYSICS;
- 0935 Seismic methods;
- EXPLORATION GEOPHYSICS;
- 0205 Archaeological geology;
- GEOHEALTH