Frequency domain electromagnetic induction survey in the intertidal zone: Limitations of low-induction-number and depth of exploration (original) (raw)
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Remote Sensing, 2022
We present a case study of multi-coil frequency-domain electromagnetic (FD-EMI) prospection of a wooden ship wreckage from the 17th century. The wreckage is buried in a sandbar in the German part of the tidal flat area of the North Sea. Furthermore, the wreckage was excavated in advance and covered again after investigation. This ground truthing background and the position of the wreckage makes it a unique investigation object to test the feasibility of FD-EMI for prospecting wooden archaeological objects in the high conductive sediments of tidal flat areas. Our results reveal the shape and position of the wreckage in terms of conductivity maps. The resulting signal change caused by the wreckage in conductivity is only 10% of the value of the water-saturated sandy background, respectively, making a cautious process necessary, including a precise height correction. The data, furthermore, reveals a sensitivity to the vertical shape of the wreckage and thus sufficient depth sensitivity...
Reconstructing palaeochannel morphology with a mobile multicoil electromagnetic induction sensor
2011
Field methods to map and reconstruct the morphology of buried river systems are highly dependent on spatial interpolation. Conventional methods, such as standard borehole survey, allow a detailed vertical reconstruction of the shallow subsurface but leave lateral connections between sample locations open to interpretation. Geophysical survey techniques have recently introduced more detail. Mobile electromagnetic induction (EMI) survey combines high density sampling with full lateral coverage but fails to produce detailed information about vertical facies changes. Recently, multicoil EMI survey added vertical discrimination potential to this lateral continuity. In this study, we present an integrated approach for reconstructing the morphology of a known palaeochannel segment by modelling the depth to the sandy substrate. In addition, a calibration method based on a limited number of auger data is proposed. In a first phase, the modelling procedure was evaluated along two transects on a test site, showing palaeochannel depths ranging from 1 to > 4 m beneath the surface. In a second phase, the morphology of the entire site was reconstructed. These three resulting depth models were then compared with auger observations and electrical resistivity tomography (ERT) data. The high correlation coefficients (> 0.9) between observed and modelled depths showed that even in complex pedological environments, palaeochannel morphology could be predicted precisely using multicoil EMI data. Therefore, we concluded that a multicoil EMI survey proves to be an efficient and reliable solution for mapping and reconstructing the morphology of the shallow subsurface.► Mobile multicoil EMI survey for mapping buried sediments. ► Palaeochannel depth modelling with electrical conductivity data. ► Calibration allows precise depth modelling in complex pedological environments. ► An efficient approach to accurately map buried land surfaces in three dimensions.
Acta Geophysica, 2016
In 2011, a geophysical survey was carried out in the surroundings of the Jagiellonian University in Cracow, using a Very Low Frequency method. The measurements were designed to determine the reason of frequent flooding of the lowest level of the building. The main objective of the study was to find out from where and in which way the rainwater seeps into the building and how this problem can be solved in the least invasive manner. The aim of geophysical methods was also to provide necessary information that will enable the construction of a hydro-geological model of the local environment. The interpretation revealed the presence of a sandy gutter surrounded by impermeable clay. There is a big resistivity contrast between those layers. Their location and approximate dimensions were determined.