P. De Smedt

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.

Habitat heterogeneity promotes intraspecific trait variability of shrub species in Australian granite inselbergs

The role of intraspecific trait variability is increasingly recognized as a key factor shaping plant fitness and community assembly worldwide. Studying the direct effects of habitat heterogeneity on trait expression of individual plants of the same species is a useful tool to quantify intraspecific trait variability locally. We investigated how habitat heterogeneity on granite inselbergs affected intraspecific trait variability of 19 functional traits in three shrub species of the family Proteaceae in south western Australia, a global biodiversity hotspot. We used pairwise comparison (single trait) and multivariate analysis (multiple traits, functional space) to detect shifts in trait patterns. Consistent with our predictions, we found that individuals developing in putatively more stressful habitats (highly sun-irradiated, shallow-soil patches on the outcrops) were characterized by trait expressions indicative of more conservative resource-related strategies when compared with plants occurring in the surrounding woodlands that were experiencing more benign ecological conditions. These results were significant for two out of three species. Granite inselbergs promoted plant longevity, a signal that these granite inselbergs might offer refugial conditions defined as protection against fire.

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.

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.