Using airborne electromagnetics surveys to investigate the hydrogeology of an area near Nyborg, Denmark

Abstract

A time‐domain airborne electromagnetic survey was flown in the County of Fyn, Denmark, immediately west of the city of Nyborg as a quick and efficient means of providing resistivity information for the development of a hydrogeological model. The bedrock geology is typified by a thick limestone overlain by a sequence of marine marl and a Quaternary moraine of variable thickness and composition. The limestone is the largest aquifer within the area and is used to supply water for Nyborg. The upper 100 m or so of the limestone generally contain fresh water and below that the groundwater is saline. The boundary between the resistive fresh water and the conductive saline water was the target of the airborne electromagnetic survey. Man‐made structures can strongly impact electromagnetic measurements; however, they can be minimized using two tactics: (1) masking the results around large power lines, and (2) non‐linear filtering of any perturbations in the interpretation that are the consequence of these or other structures. The latter strategy is possible because of the dense areal coverage provided by the airborne survey, and is particularly useful when a regional overview is required. Resistivity sections derived from the airborne electromagnetic data indicate a resistive zone of till, diluvial sand and freshwater limestone of variable thickness above a deeper conductive zone of saline water. A conductive layer within the moraine, assumed to be clay or marl, is also occasionally indicated. We used a two‐layer model to estimate the depth to the freshwater/saline‐water interface. Where ground soundings have been made, the depth estimates from the ground and airborne data agree. The depth estimates from the airborne data can be used to infer the thickness of the freshwater aquifer, either locally or regionally.

Airborne time‐domain electromagnetics, electrical resistivity and seismic reflection for regional three‐dimensional mapping and characterization of the Spiritwood Valley Aquifer, Manitoba, Canada

“…Applicability of these systems for regional mapping of near‐surface resistive materials has yet to be soundly established both in terms of target identification, data collection and processing (e.g., Martinez et al ). Canadian commercial time‐domain AEM systems have been utilized in groundwater studies for salinity mapping (e.g., Smith et al ) and groundwater prospecting in arid environments (e.g., Wynn et al ; Baldridge et al ). However, these applications represent the detection/location of conductive targets in a variably resistive host with a strong contrast.…”

A new tool available for hydrogeologists: the Airborne EM method

“…Nel caso ad esempio dello studio dell'intrusione marina nelle falde costiere, il metodo sfrutta l'elevata conducibilità elettrica del cuneo salino, un target quindi ottimale per i metodi EM. Per citare solo alcuni dei più importanti lavori pubblicati: Fitterman e Deszcz-Pan, 1998; Siemon et al, 2004;Smith et al, 2004;Siemon, 2006, Viezzoli et al, 2010. E' stato inoltre utilizzato per studiare la contaminazione di falde acquifere da parte di acque mineralizzate Munday e Fitzpatrick, 2008), l'individuazione di paleovalli acquifere (Christiansen et al, 2006;Auken et al, 2008;Sapia et al, 2014), sino alla ricerca di corpi idrici sotterranei Danielsen et al, 2003;Sattel e Kgothlang, 2004;Baldridge et al, 2007;Christensen et al, 2008;Steuer et al, 2008).…”

Inversion of airborne time‐domain electromagnetic data to a 1D structure using lateral constraints

“…Map of the Fyn survey area near Nyborg, Denmark. The location of Line 138 is indicated with an arrow (from Smith et al ).…”

“…One strategy is to mask or discard the results around man-made Map of the Fyn survey area near Nyborg, Denmark. The location of Line 138 is indicated with an arrow (from Smith et al 2004).…”