Journal ArticleDOI
SkyTEM–a New High-resolution Helicopter Transient Electromagnetic System
Kurt Sørensen,Esben Auken +1 more
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TLDR
SkyTEM as mentioned in this paper is a time-domain, helicopter electromagnetic system designed for hydrogeophysical and environmental investigation, which is a rapid alternative to ground-based, transient electromagnetic measurements, the resolution capabilities are comparable to that of a conventional 40 × 40 m 2 system.Abstract:
SkyTEM is a time-domain, helicopter electromagnetic system designed for hydrogeophysical and environmental investigation. Developed as a rapid alternative to ground-based, transient electromagnetic measurements, the resolution capabilities are comparable to that of a conventional 40 × 40 m 2 system. Independent of the helicopter, the entire system is carried as an external sling load. In the present system, the transmitter, mounted on a lightweight wooden lattice frame, is a four-turn 12.5 × 12.5 m 2 square loop, divided into segments for transmitting a low moment with one turn and a high moment with all four turns. The low moment uses about 30 A with a turn-off time of about 4 µs; the high moment draws approximately 50 A, and has a turn-off time of about 80 µs. The shielded, overdamped, multi-turn receiver loop is rigidly mounted on the side of the transmitter loop. This is essentially a central-loop configuration with a 1.5 m vertical offset. In vertical hover mode the SkyTEM responses were within 2% of those from a conventional ground-based system. Instrument bias level is not a concern as high-altitude tests showed that the background noise level is higher than the instrument bias level. By inverting a sounding from a test site to a standard model and then applying the SkyTEM system parameters to compute the forward response, conventional measurements were within 5% of SkyTEM responses for flight heights of 7.25, 10, and 20 m. Standard field operations include establishment of a repeat base station in the survey area where data are acquired approximately every 1.5 hours, when the helicopter is refuelled, to monitor system stability. Data acquired in a production survey were successful in detecting and delineating a buried-valley structure important in hydrogeophysical investigations.read more
Citations
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Journal ArticleDOI
Advancing process‐based watershed hydrological research using near‐surface geophysics: A vision for, and review of, electrical and magnetic geophysical methods
David A. Robinson,Andrew Binley,N. Crook,Frederick D. Day-Lewis,Ty P. A. Ferré,V. J. S. Grauch,Rosemary Knight,Michael D. Knoll,Venkat Lakshmi,Richard D. Miller,Jonathan E. Nyquist,L. Pellerin,Kamini Singha,Lee Slater +13 more
TL;DR: The paper identifies instruments, provides examples of their use, and describes how synergy between measurement and modelling could be achieved, and provides a vision for the use of electrical and magnetic geophysical instrumentation in watershed scale hydrology.
Journal ArticleDOI
Quasi-3D modeling of airborne TEM data by spatially constrained inversion
TL;DR: In this paper, a new methodology, spatially constrained inversion (SCI), is proposed to produce quasi-3D conductivity modeling of electromagnetic (EM) data using a 1D forward solution.
Journal ArticleDOI
An overview of a highly versatile forward and stable inverse algorithm for airborne, ground-based and borehole electromagnetic and electric data
Esben Auken,Anders Vest Christiansen,Casper Kirkegaard,Gianluca Fiandaca,Cyril Schamper,Ahmad A. Behroozmand,Ahmad A. Behroozmand,Andrew Binley,Emil Krabbe Nielsen,Flemming Effersø,Niels B. Christensen,Kurt Sørensen,Nikolaj Foged,Giulio Vignoli,Giulio Vignoli +14 more
TL;DR: In this paper, the authors present a modular forward response algorithm that is independent of data type, making it easy to add support for new types of data types and instrument geometries.
Journal ArticleDOI
A review of helicopter‐borne electromagnetic methods for groundwater exploration
TL;DR: In this paper, the advantages and limitations of airborne electromagnetic (AEM) surveys compared to ground-based geophysical methods used in groundwater surveys are discussed, based on typical field examples.
Journal ArticleDOI
Buried and open tunnel valleys in Denmark—erosion beneath multiple ice sheets
TL;DR: Tunnel valleys are large, elongate and irregular depressions cut beneath the margin of former ice sheets as mentioned in this paper, and they play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour.
References
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Journal ArticleDOI
Depth of investigation in electromagnetic sounding methods
TL;DR: The time or frequency at which the electromagnetic response of a buried inhomogeneity can first be measured is determined by its depth of burial and the average conductivity of the overlying section; it is relatively independent of the type of source or receiver and their separation.
Journal ArticleDOI
Transient Electromagnetic Sounding for Groundwater
TL;DR: The feasibility of using the transient electromagnetic sounding (TS or TDEM) method for groundwater exploration can be studied by means of numerical models as discussed by the authors, which is best suited for locating conductive targets, and has very good vertical resolution.
Journal ArticleDOI
The application of the transient electromagnetic method in hydrogeophysical surveys
TL;DR: In this article, the authors show that for a valley structure in a low-resistive layer, the 1-dimensional assumption is sufficient to track the presence of rather steep slopes, however, the insensitivity of the TEM method to resistors makes it difficult to determine a slope with a 1-D inversion and only the overall structure is defined.