Reconstructing palaeochannel morphology with a mobile multicoil electromagnetic induction sensor (original) (raw)
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Archaeological …
Multiple apparent electrical conductivity (ECa) measurements with an electromagnetic induction (EMI) sensor frequently reveal analogue patterns caused by conductive features in the soil. A procedure was proposed to highlight different archaeological anomalies based on combinations of the simultaneous ECa measurements with the DUALEM-21S instrument. After selection of a 3.5 ha study site, 0.79 ha has been recorded by archaeological excavation. Since the majority of the archaeological features were found between the plough layer and 1.0 m below the soil surface, a set of four equations were developed to model the EC within that predefined depth interval. This set of four equations employed the four depth response curves specific to the four DUALEM-21S coil configurations. The modelled conductivity between 0.5 and 1.0 m (inline image) showed a larger variability across the archaeological features than the raw EC data. To quantify the added value of this modelled conductivity, inline image and measured ECa were compared with the rasterized map of the archaeological traces. Finally, the inline image map proved to be better able to distinguish between the archaeological features and the ‘empty’ background. This technique allowed the highlighting of vague anomalies in the simultaneous DUALEM-21S ECa measurements. Copyright © 2012 John Wiley & Sons, Ltd.
Mapping depth-to-clay using fitted multiple depth response curves of a proximal EMI sensor
Geoderma, 2011
As an alternative for the depth response approximations based on the theoretical Maxwell's equations, a procedure was proposed to fit depth response curves for different coil configurations. A 39 ha study area was selected in the Belgian loess belt, where loess material was situated on a Tertiary substrate. A survey with the DUALEM-21S electromagnetic induction instrument was carried out to map the depth-to-clay (z clay ). The depth response curves were fitted both for the vertical and perpendicular coil configurations using 85 depth observations of z clay . The resulting depth response curves R(z clay ) were:
European Journal of Soil Science, 2019
The identification of buried soil horizons in agricultural landscapes helps to quantify sediment budgets and erosion-related carbon dynamics. High-resolution mapping of buried horizons using conventional soil surveys is destructive and time-consuming. Geoelectrical sensors can offer a fast and non-destructive alternative for determining horizon positions and properties. In this paper, we compare the suitability of several geoelectrical methods for measuring the depth to buried horizons (Apb, Ahb, and Hab) in the hummocky ground moraine landscape of northeastern Germany. Soil profile descriptions were developed for 269 locations within a 6-ha experimental field "CarboZALF-D". A stepwise linear discriminant analysis (LDA) estimated the lateral position of the buried horizons using electromagnetic induction data and terrain attributes. To predict the depth of a buried horizon, multiple linear regression (MLR) was used for both a 120 m transect and a 0.2 ha pseudo-3D area. At these scales, apparent electrical conductivity (EC a), electrical resistivity (ER) and terrain attributes were used as independent variables. The LDA accurately predicted Apb-and Ahb-horizons (a correct classification of 93 %). The LDA of the Hab-horizon had a misclassification of 24 %, which was probably related to the smaller test set and the higher depth of this horizon. The MLR predicted the depth of the Apb-, Ahb-and Hab-horizons with relative root mean square errors (RMSEs) of 7 %, 3 % and 13 %, respectively, in the pseudo-3D area. MLR had a lower accuracy for the 2D transect compared to the pseudo-3D area. Overall, the use of LDA and MLR has been an efficient methodological approach for predicting buried horizon positions.
Hydrology and Earth System Sciences Discussions, 2017
The La Bassée floodplain area is a large groundwater reservoir controlling most of the water exchanged between local aquifers and hydrographic networks within the Seine River Basin (France). Preferential flows depend essentially on sediment fills, whose characteristics are strongly influenced by paleomeander heterogeneities. A detailed knowledge of the internal heterogeneities of such paleomeanders can thus lead to a comprehensive understanding of its long-term hydrogeological processes. A geophysical survey based on the use of electromagnetic induction was performed on a representative paleomeander, situated close to the city of Nogent-sur-Seine in France. In the present study we assess the advantages of combining several spatial offsets, together with both vertical and horizontal dipole orientations (6 apparent conductivities), thereby mapping not only the spatial distribution of the paleomeander derived from LIDAR data, but also its vertical extent and internal variability.
Journal of Geophysics and Engineering
This study focuses on the integrated application of the frequency-domain terrain conductivity (TC) and transient electromagnetic (TEM) methods to map an ancient riverine harbour (port) at the Egyptian archaeological site of Tell el-Rub'a (prehistoric Mendes). Fifty-one TC profiles were measured using six EM frequencies and 16 TEM soundings were performed at the selected site. The apparent conductivity maps derived from the TC survey enabled defining the lateral extension of the harbour basin and its edges to penetration depths ranging between 12 and 30 m. The vertical extension of the harbour basin was determined using the TEM inversion. Three layers were defined: the topsoil, the conductive silty clay infill and the resistive sand bedrock. The bedrock is found at depths ranging from 19 to 31 m. The TC and TEM results were combined to form a 3D image of the harbour basin. This study confirms the existence of Mendes harbour and demonstrates the effectiveness of the TC and TEM met...
The archaeological evaluation of landscapes in the framework of developer-led archaeology is often based on extensive trenching programmes complemented with auger surveys in wetland environments. During the archaeological evaluation of a 90 ha polder site in the north-west of Belgium, a mobile multi-receiver electromagnetic induction (EMI) survey was used as a main prospecting technique. The use of a mobile survey allowed to map the entire study area at a very fine resolution (over 25 measurements per m2). Incorporating a multi-receiver EMI instrument enabled measuring the apparent electrical conductivity (ECa) and the apparent magnetic susceptibility (MSa) of four different soil volumes simultaneously at each location. The detailed maps provided insight into the archaeological and geomorphological features of the site. Among the detected structures were a large medieval farmstead, a palaeoriver system and a number of military remains from World War I (WWI). The vertical discrimination potential added insight into the vertical facies changes, which allowed modelling the palaeolandscape and helped determining the depth of detected medieval features. The different MSa measurements gave additional insight into the WWI structures. In this paper, we give an overview of the possibilities of combining multiple ECa measurements for interpreting vertical soil variability together with an example of the added information from simultaneously gathered MSa data. More generally, the diverse potential of multi-receiver EMI survey for geoarchaeological research is demonstrated.
Remote Sensing, 2016
Increasingly, electromagnetic induction methods (EMI) are being used within the area of archaeological prospecting for mapping soil structures or for studying paleo-landscapes. Recent hardware developments have made fast data acquisition, combined with precise positioning, possible, thus providing interesting possibilities for archaeological prospecting. However, it is commonly assumed that the instrument operates in what is referred to as Low Induction Number, or LIN. Here, we detail the problems of the approximations while discussing a best practice for EMI measurements, data processing, and inversion for understanding a paleo-landscape at an Iron Age human bone depositional site (Alken Enge) in Denmark. On synthetic as well as field data we show that soil mapping based on EMI instruments can be improved by applying data processing methodologies from adjacent scientific fields. Data from a 10 hectare study site was collected with a line spacing of 1-4 m, resulting in roughly 13,000 processed soundings, which were inverted with a full non-linear algorithm. The models had higher dynamic range in the retrieved resistivity values, as well as sharper contrasts between structural elements than we could obtain by looking at data alone. We show that the pre-excavation EMI mapping facilitated an archaeological prospecting where traditional trenching could be replaced by a few test pits at selected sites, hereby increasing the chance of finding human bones. In a general context we show that (1) dedicated processing of EMI data is necessary to remove coupling from anthropogenic structures (fences, phone cables, paved roads, etc.), and (2) that carrying out a dedicated full non-linear inversion with spatial coherency constraints improves the accuracy of resistivities and structures over using the data as they are or using the Low Induction Number (LIN) approximation.
Journal of Environmental & Engineering Geophysics, 2013
The purpose of this paper is to evaluate the effectiveness of large loop, ground-based, time-domain electromagnetic surveys for modeling of paleovalley geometry and valley fills as a basis for determining groundwater potential. The electromagnetic (EM) survey was successful, despite limited resistivity contrast between adjacent valley-fill units, as well as the limited contrast between the valley-fill and bedrock. Thin, coarse-grained units and low contrast in the resistivity present challenges for constraining 1-D inversions. Thin units cannot be resolved and are merged, resulting in simplified models that reflect averaged apparent resistivity. Supplementary data (e.g., borehole resistivity logs) are useful for constraining complex multilayer inversions, but where absent, complex models are not realistic. As the ratio of the resistivity of two layers decreases, there is more uncertainty in the placement of layer boundaries even though the root mean squared standard error of fit for the model may remain small (,6%). Nonetheless, when 1-D inversions are combined into resistivity-depth sections we interpret four generalized lithologies: 1) bedrock (,10-30 ohm-m); 2) fine-grained sediment (clay, silt, fine sand, and diamict; 30-50 ohm-m); 3) medium-grained sediment (silt and sand; 40-80 ohm-m); and 4) coarse-grained sediment (sand and possibly gravel; 90 to .350 ohm-m). When the 2-D resistivity-depth sections are combined, there is 3-D continuity and the geometry of the Groundbirch Paleovalley can be traced. The valley is approximately 3-4 km wide with a maximum depth of about 120 m. The data suggest a local basal aquifer (medium-to coarsegrained unit) in the central survey area and possibly an unconfined aquifer towards the northwest region of the survey area. The EM-based model is consistent with models based on water well logs and field observations. Although the EM data remain exploratory, the resulting EM models provide clear guidance for groundwater resources management strategies.
Archaeological Prospection, 2019
Electrical resistivity tomography (ERT) surveys were conducted at the Velika Pe cina near Kli cevica and Romuald's Cave sites in Croatia in 2014 and 2015. The goal of the surveys was to estimate sediment depth to bedrock. However, neither survey produced reliable results at the 0.5 m probe spacing. In 2017, the Romuald's Cave site was revisited utilizing a high data density survey of 0.1 m probe spacing. All three surveys were conducted with a GeoScan RM85 in a pole-pole configuration. The high data density survey produced reliable results given the subsurface information available from three excavation trenches in the first chamber of the cave. The 2015 and 2017 ERT survey results are presented along with the results from two additional high data density ERT surveys located in the back chamber of Romuald's Cave. These results suggest that utilizing high data densities may improve the reliability of ERT surveys in cave environments. K E Y W O R D S cave site, early Mesolithic, Adriatic regionelectrical resistivity tomographyPaleolithicsediment depth estimation