Time-Lapse Airborne EM Surveys Across a Municipal Landfill

Beamish, David; Mattsson, A.

doi:10.4133/jeeg8.3.157

Cited by 11 publications

(4 citation statements)

References 14 publications

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“…In the latter part of the 1990's, Fitterman and Deszcz-Pan (1998) discussed the use of multi-date AEM data for as a means of assessing long term changes in the aquifer system resulting from changes in water management policies aimed at restoring the South Florida ecosystem. Beamish and Mattsson (2003) reported on the application of repeat AEM surveys in relation to the long-term monitoring of large, active, contain and seal landfills. Results from a comparison of two frequency domain helicopter EM data sets acquired a year apart were analysed by Lipinski et al (2008).…”

Section: Introductionmentioning

confidence: 99%

Resolving Changes to Freshwater Lens Systems in a “Sea of Salinity” using Multi-date Airborne EM

Munday¹,

Soerensen²

2018

ASEG Extended Abstracts

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Saline aquifers in the Murray River or SE Australia are traversed by freshwater rivers, with adjoining riparian and floodplain regions containing freshwater lenses. Bore data and more recent Airborne electromagnetic (AEM) surveys have determined that these lenses are spatially extensive, but have widely varying geometries. The maintenance of these lens systems is important as they support ecologically significant riparian vegetation communities such as Red Gum and Black Box. A more complete understanding of their hydrogeology is required to ascertain how they develop and degrade. Limited ground investigations including 14 C geochemistry have determined that the lens systems contain recent water, indicating that they are dynamic systems with their development defined by the relative rates of recharge from the river and mixing with groundwater. Changes in groundwater gradients and depth, floodplain extent, and topography are believed to control their initial location. The same controls also govern their stability. The potential of AEM systems for defining the geometry of these lens systems in 3D is considered along with an assessment of their value for monitoring variations associated with these ecosystems. The advent of "calibrated" AEM systems and robust inversion tools have given added impetus to their use for environmental monitoring. Spatio-temporal variations are observed in the near surface (top 20m) from a multi-temporal assessment of Clark's Floodplain, adjacent to the Bookpurnong irrigation area, with co-incident AEM surveys acquired between 2008 and 2015. Spatial changes in ground conductivity, attributed to changing groundwater quality have been observed. The freshwater lens systems appear to have contracted significantly over the last decade. This is attributed, in part, to land use patterns and the development of an irrigation-related groundwater mound on the highlands adjacent to the floodplain, and an increased hydraulic gradient towards the river. The results indicate the geometry of the hyporheic zone may have also changed along the river.

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Section: Introductionmentioning

confidence: 99%

Resolving Changes to Freshwater Lens Systems in a “Sea of Salinity” using Multi-date Airborne EM

Munday¹,

Soerensen²

2018

ASEG Extended Abstracts

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“…Products may include time constant calculations, apparent conductance/conductivity, chargeability, and conductivity depth transforms/inversions. For these reasons, the use of this technology has been extended to a variety of applications in addition to mineral exploration, including petroleum exploration (Paine et al, 1997), hydrogeology (Smith et al, 2004), and environmental research (Shang et al, 2001;Beamish and Mattsson, 2003).…”

Section: Introductionmentioning

confidence: 99%

Quantifying the Effects That Changes in Transmitter-Receiver Geometry Have on the Capability of an Airborne Electromagnetic Survey System to Detect Good Conductors

Hefford

Smith

Samson

2006

Exploration and Mining Geology

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Time-domain electromagnetic systems are most sensitive to highly conductive targets during the transmitter on-time. Data collected during the on-time is highly influenced by the geometric relationship between the transmitter and the receiver. Unless corrections can be applied for these geometric variations, the ability to correctly detect and identify highly conductive targets can not be fully realized. Variables affecting the relative position between the transmitter and receiver include changes in the position of the receiver with respect to the transmitter, variations in transmitter attitude, and transmitter loop deformation. The level of accuracy in the determination of the relative geometry required to permit complete removal of the effects due to geometric variations is different for each of the variables and is dependent on the depth of the target. The most influential geometric variation involves changes in the relative position of the receiver with respect to the transmitter along the direction of flight; this variable, therefore, requires the highest degree of accuracy. The accuracy required for receiver motions along the vertical direction is roughly one order of magnitude less, and in the lateral direction, several orders of magnitude less. The objective of this paper is to relate the sensitivity of the response to transmitter-receiver geometry to the ability of an airborne, time-domain electromagnetic system to resolve a highly conductive vertical target. This is achieved by a detailed analysis of the effect of the individual x, y, and z distances between the transmitter and the receiver, the transmitter attitude (roll, pitch, and yaw), and transmitter deformation.

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“…There is a distinction between this form of general surveying and localised site specific environmental AEM surveys that have been conducted across potentially hazardous areas (e.g. Doll et al, 2000;Beamish and Mattsson, 2003).…”

Section: Introductionmentioning

confidence: 99%

3D modelling of near-surface, environmental effects on AEM data

Beamish¹

2004

Journal of Applied Geophysics

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This study considers the 3D modelling of compact, at-surface conductive bodies on frequency domain airborne electromagnetic (AEM) survey data. The context is the use of AEM data for environmental and land quality applications. The 3D structures encountered are typically conductive, of limited thickness (< 20 m) and form 'point' source locations carrying potential environmental risk. The scale of such bodies may generate single profile, 'bulls-eye' anomalies. In attempts to recover geological information, such anomalies may be considered to represent noise. In environmental AEM, the correct interpretation of such features is important. The study uses a combination of theoretical models and trial fixed wing survey data obtained in populated areas of the UK. Scale issues are discussed in terms of the volumetric footprints of the induced electric field generated by systems flown at both low and high elevation. One of the primary uses of AEM survey data lies in the assessment of conductivity maps. These are typically obtained using 1D conductivity models at individual measurement points. In order to investigate the limitations of this approach, 3D modelling of conductive structures with dimensions less than 350 x 350 m and thicknesses extending to 20 m has been carried out. A 1D half space inversion of the data obtained at each frequency is then used to assess the behaviour of the spatial information. The results demonstrate that half space conductivity values obtained over compact 3D targets generally provide only apparent conductivity results. For thin, atsurface bodies, conductivity values are biased to lower values than the true conductivity except at high frequency.The spatial perturbation to both coupling ratios and 1D conductivity models can be laterally extensive. The results from 3D modelling indicate that the use of horizontal derivatives applied to the conductivity models offers enhanced edge detection. The practical application of such derivatives to both regional and local scale survey data is presented.. The special case of a near-surface, metallic pipeline has been modelled. The problem constitutes an inductive limit (current gathering) response in which the perturbation is largely confined to the in-phase coupling ratios. The main perturbations, in data and conductivity models, are within about 40 m of each side of the pipeline. The maximum perturbation to the conductivity model is only a factor of 1.5 above background. Detailed survey data across a former compact landfill (about 100 x 100 m) are used to compare the model behaviour predicted by the 3D modelling with survey results. The survey, conducted at two separate altitudes, provides a demonstration of 3D effects on 1D survey models as a function of frequency and elevation. Although the nature of the landfill materials and their location are not known precisely, the mapping information appears realistic.

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Time-Lapse Airborne EM Surveys Across a Municipal Landfill

Cited by 11 publications

References 14 publications

Resolving Changes to Freshwater Lens Systems in a “Sea of Salinity” using Multi-date Airborne EM

Resolving Changes to Freshwater Lens Systems in a “Sea of Salinity” using Multi-date Airborne EM

Quantifying the Effects That Changes in Transmitter-Receiver Geometry Have on the Capability of an Airborne Electromagnetic Survey System to Detect Good Conductors

3D modelling of near-surface, environmental effects on AEM data

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