Timothy Saey

Combining multiple signals of an electromagnetic induction sensor to prospect land for metal objects

Buried unexploded ammunition is a major problem on arable land in former battle areas. Many battlefields of the First World War (WWI) still contain a lot of unexploded shells just below the plough layer, posing serious threats to soil editors and trenchers. Electromagnetic induction (EMI) sensors have been used for a variety of agricultural and archaeological purposes to map the natural soil variability and to locate buried archaeological remains. Besides its sensitivity to variations in soil texture and anthropogenic disturbances, EMI proves to respond strongly to metal objects in the soil. Most EMI sensors rely on a single signal, with magnitude and sign of the metal anomalies differing according to the instruments coil distance and separation. The multi-coil EMI sensor, the DUALEM-21S, provides four simultaneous apparent electrical conductivity ( ECa ) signals enhancing significantly the possibilities for signal processing. To calibrate our instrument, we buried different masses of metal at different depths. The four ( ECa measurements showed a response to the metal objects down to 1.2 m. The measurements were subtracted by their gradual trend to obtain the local anomalies (Δ( ECa ). A combination of these four Δ( ECa ’s was used to amplify the signal response to metal, influenced by both depth and mass of the buried objects. At an intensively shelled former WWI battle field near Ypres (Belgium), a detailed prospection was conducted with the DUALEM-21S. Based on our multi-signal procedure, we located 40 positions, 20 where we predicted buried metal and 20 where we expected that no metal was present within 1.2 m depth. There were no false negative predictions and at the 20 locations where we expected metal, shells up to 90 kg were excavated. As a final outcome we produced a map with predictions of the mass of metal objects in the soil assuming a fixed depth and alternatively a map with predictions of the depth of metal objects assuming a given mass. Apart from their potential for agricultural and archaeological investigations, multi-( ECa signals were shown to be useful for locating metal objects, like unexploded WWI shells, in the top 1.2 m of soil.

The discovery of the school of gladiators at Carnuntum, Austria

Sophisticated techniques of archaeological survey, including airborne imaging spectroscopy, electromagnetic induction and ground-penetrating radar, are opening up new horizons in the non-invasive exploration of archaeological sites. One location where they have yielded spectacular results is Carnuntum in Austria, on the south bank of the Danube, capital of the key Roman province of Pannonia. Excavations in the late nineteenth and twentieth centuries revealed many of the major elements of this extensive complex, including the legionary fortress and the civilian town or municipium. Excavation, however, is no longer the only way of recovering and recording the details of these buried structures. In 2011, a combination of non-invasive survey methods in the area to the south of the civilian town, where little was visible on the surface, led to the dramatic discovery of remains interpreted as a gladiatorial school, complete with individual cells for the gladiators and a circular training arena. The combination of techniques has led to the recording and visualisation of the buried remains in astonishing detail, and the impact of the discovery is made all the greater by the stunning reconstruction images that the project has generated.

The 3-D reconstruction of medieval wetland reclamation through electromagnetic induction survey

Studies of past human-landscape interactions rely upon the integration of archaeological, biological and geological information within their geographical context. However, detecting the often ephemeral traces of human activities at a landscape scale remains difficult with conventional archaeological field survey. Geophysical methods offer a solution by bridging the gap between point finds and the surrounding landscape, but these surveys often solely target archaeological features. Here we show how simultaneous mapping of multiple physical soil properties with a high resolution multi-receiver electromagnetic induction (EMI) survey permits a reconstruction of the three-dimensional layout and pedological setting of a medieval reclaimed landscape in Flanders (Belgium). Combined with limited and directed excavations, the results offer a unique insight into the way such marginal landscapes were reclaimed and occupied during the Middle Ages. This approach provides a robust foundation for unravelling complex historical landscapes and will enhance our understanding of past human-landscape interactions.

The Ypres Salient 1914–1918: Historical Aerial Photography and the Landscape of War

Abstract As the centenary commemorations of the Battle of Passchendaele approach, this article is a timely demonstration of how archaeology can provide new insights into the landscape of the Western Front. Assessment of over 9000 aerial photographs taken during the First World War, integrated with other approaches to landscape archaeology, offers a new perspective on the shifting nature of the historic struggle around the town of Ypres in Belgium. The results not only illustrate the changing face of the landscape over that four-year period, but also highlight the potential of aerial photographic records to illuminate hitherto overlooked aspects of landscape heritage.

A neural network approach to topsoil clay prediction using an EMI-based soil sensor

High-resolution proximal soil sensor data are an important source of information for optimising the prediction of soil properties. On a 10.5 ha arable field, an intensive EM38DD survey with a resolution of 2 m × 2 m resulted in 19,694 measurements of ECa-H and ECa-V. A large textural variation was present in the subsoil due to the presence of former water channels. Nevertheless, both ECa-V and ECa-H data displayed the same spatial variability. This spatial similarity indicated the strong influence of the subsoil heterogeneity on the ECa-H measurements. Using variography, two scales of ECa variability were identified: short-range (∼35 m) variability associated with the channel pattern and wider within-field variability (∼200 m). Using artificial neural networks (ANNs), prediction of the topsoil clay content was optimised (i) by using an input window size of 3, 5, 7, 9, and 11 pixels to account for local contextual influence and (ii) by including both ECa-H and ECa-V in the network input layer to isolate the response from the topsoil. The models were evaluated using R 2 and the relative mean squared estimation error (rMSEE) of the test data. The most accurate predictions were obtained using both orientations of the EM38DD sensor without contextual information (R 2 = 0.66, rMSEE = 0.40). The importance of ECa-V on the topsoil clay prediction was expressed by a relative improvement of the rMSEE of 29%. For comparison, a multivariate linear regression (MVLR) was performed to predict the topsoil clay content based on the two orientations. The ANN models up to a window size of 5 pixels outperformed the MVLR, which resulted in an R 2 of 0.42 and an rMSEE of 0.63. ANN analysis based on both orientations of the EM38DD appears to be a useful tool to extract topsoil information from depth-integrated EM38DD measurements.

Using the past to indicate the possible presence of relics in the present-day landscape: the Western Front of the Great War in Belgium

Abstract The First World War (WWI) had a notable influence on the landscape at the former Western Front in Belgium. Research on a landscape scale is necessary to understand the destructive and constructive impact of the war and its consequences for the post-war landscape in a holistic manner. This paper focuses on the trajectory and impact analysis of three study areas with contrasting landscape types and aims to indicate possible preserved military relics today. Therefore, landscape changes are studied using historical aerial photographs (WWI and WWII) and contemporary orthophotos. A military landscape characterisation is made based on land use/land cover and linear structures that were mapped throughout time. Specific landscape trajectories could be designated as areas with a possible preservation of WWI heritage, with a related impact degree. The results are useful for sustainable heritage management and for further interdisciplinary research on WWI-heritage, by providing a broad knowledge of the area.

Potential for Reconstruction of the Subsurface Salinity Distribution Using the Frequency Domain Electromagnetic Method

We explore the usefulness of FDEM conductivity mapping for hydrogeological investigations by surveying farming land overlying a salt plume. Specifically the potential for reconstructing the salinity distribution of the subsurface is researched. To this end, calibration of the collected FDEM data and accuracy of the inverted responses are looked into. In addition, ancillary data were collected to validate the results.

Increasing Positional Accuracy of Surveys - Correcting for Spatial Offset and Time Lag

To evaluate the degree of loss of positional accuracy when a spatial offset is present between position and sensor data, we have simultaneously collected GNSS data (with RTK correction) using a GNSS receiver that was mounted on an ATV and two other receivers that were mounted on the front and end of an elongate sled. Comparing the predicted locations with the actual positions allowed to quantify and visualize the prediction error. As a result, the strengths and weaknesses of applied corrections can be evaluated, allowing to select an appropriate correction for a given survey implementation.

Multi-receiver EMI to Support Precision Agriculture within the Western Front Zone

Electromagnetic induction (EMI) sensing has proven effective to support site-specific soil management for precision agriculture. Within the Western World War (WW I) front zone, invasive practices are hampered by the presence of unexploded ammunition. Therefore, non-invasive EMI sensing has the potential to provide both information about the soil variability and the presence of buried metal objects. With this research, both could be separated deliberately.

Integrating GPR and EMI to three-dimensionally reconstruct a WW I training trench at Stonehenge

Given the upcoming centennial commemoration of the beginning of the Great War (WW I), the international attention for this conflict grows considerably. Questions will be raised about the nature of this heritage. In this study, we focus on a WW I training trench which was built in the Stonehenge (UK) World Heritage landscape where no fighting took place. Frequency-domain GPR and multi-receiver EMI were used to characterize this trench network in 3-D. The GPR measurements showed the trench infillings as strong reflections contrasting with the surrounding loess-chalk soil. However, converting the two-way travel times to absolute depths requires knowledge of the relative permittivity ε. Due to the impossibility to perform invasive observations in this protected landscape, we developed a procedure to integrate the GPR measurements with EMI magnetic susceptibility (κ) measurements. A fitting procedure allowed to estimate both the of the trench infilling and the surrounding soil material, and the ε of the material above and within the trench. This rendered absolute depth values to the GPR reflection data, improving the exact characterization of the trench system. Moreover, these results allowed to obtain depth-slices from EMI κa data. So integrating both GPR and EMI measurements enabled the 3-D reconstruction of the buried trench network.