Marc Van Meirvenne

A practical guide to performing multiple-point statistical simulations with the Direct Sampling algorithm

The Direct Sampling (DS) algorithm is a recently developed multiple-point statistical simulation technique. It directly scans the training image (TI) for a given data event instead of storing the training probability values in a catalogue prior to simulation. By using distances between the given data events and the TI patterns, DS allows to simulate categorical, continuous and multivariate problems. Benefiting from the wide spectrum of potential applications of DS, requires understanding of the user-defined input parameters. Therefore, we list the most important parameters and assess their impact on the generated simulations. Real case TIs are used, including an image of ice-wedge polygons, a marble slice and snow crystals, all three as continuous and categorical images. We also use a 3D categorical TI representing a block of concrete to demonstrate the capacity of DS to generate 3D simulations. First, a quantitative sensitivity analysis is conducted on the three parameters balancing simulation quality and CPU time: the acceptance threshold t, the fraction of TI to scan f and the number of neighbors n. Next to a visual inspection of the generated simulations, the performance is analyzed in terms of speed of calculation and quality of pattern reproduction. Whereas decreasing the CPU time by influencing t and n is at the expense of simulation quality, reducing the scanned fraction of the TI allows substantial computational gains without degrading the quality as long as the TI contains enough reproducible patterns. We also illustrate the quality improvement resulting from post-processing and the potential of DS to simulate bivariate problems and to honor conditioning data. We report a comprehensive guide to performing multiple-point statistical simulations with the DS algorithm and provide recommendations on how to set the input parameters appropriately.

Spatial Estimation of Reference Evapotranspiration in Andalusia, Spain

Abstract Knowledge of the spatial and temporal distribution of reference crop evapotranspiration (ET0) is of interest for regional water resources management, especially in areas of the world where fine-tuning of agricultural water demands over large areas is required. This study provides a strategy for mapping ET0 in regions with low meteorological data availability. For Andalusia, Spain, it involves estimating ET0 from temperature data using a locally calibrated version of the Hargreaves equation and the application of geostatistical interpolation techniques that take into account elevation as secondary information. Average annual ET0 at 191 observatories (with elevation between 0 and 1260 m) ranged from 954 to 1460 mm, with an average of 1283 mm, a standard deviation of 99 mm, and a correlation coefficient with elevation of −0.86. Simple kriging with varying local means (SKlm) and kriging with an external drift (KED)—two methods that take into account elevation as secondary information—increased spatia...

Is the Soil Variability within the Small Fields of Flanders Structured Enough to Allow Precision Agriculture

The average area of agricultural fields in Flanders (Belgium) is about 1.7 ha, being very small compared to fields where precision agriculture is currently applied. Therefore this paper addresses the question whether the within-field variation of soil properties in such fields is structured enough to motivate precision agriculture. To answer this question, 9 soil properties determined on 380 soil samples located in 77 agricultural fields situated in the 5 most dominant pedoscapes of Flanders were used to analyze their spatial variation over intervals ranging from 5 to 900 m. The data set was subjected to a principal component analysis which identified two principal components (PCs) explaining more than 78% of the total variance. The first PC represented the chemical soil properties and the second the physical and biological properties. A variogram analysis of the scores on these two PCs showed that the micro-scale and random variation dominated (82%) the within-field variability of the first PC. The within-field variability of the second PC was dominantly spatially structured (only 37% micro-scale and random variation). Therefore, it was concluded that mainly for soil physical and biological properties (like soil textural fractions and organic matter), the average within-field variation in the small fields of the investigated landscapes is structured enough to allow precision agriculture.

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.

Small-scale seed bank patterns in a forest soil

The forest seed bank has been demonstrated to vary spatially at scales from 2 to 10 m. To our knowledge, the fine-scale spatial structure, i.e. < 2 m, has not been studied before. This study aims to make a thorough investigation of fine-scale spatial structure. Soil samples (128) were collected from each of five 2.1 m × 2.1 m plots, using a combined systematic (64) and random design (64). This allowed investigation of the fine-scale spatial structure of individual species–plot combinations using indicator-variograms. Our results indicated that over half of all species recorded in a particular plot were spatially structured. Remarkably, the presence of spatial structure seemed independent of species frequency. Visualization of the spatial structure showed an irregular spatial pattern, i.e. seed clusters that were randomly distributed in space. Spatial dependence occurred over small distances, possibly suggesting that a significant proportion of seeds was deposited near the mother plant. We conclude by presenting the relevance and implications of small-scale spatial seed-bank patterning for seed-bank sampling.

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.

Accounting for Surface Refraction in Velocity Semblance Analysis With Air-Coupled GPR

The aim of this study is to evaluate the velocity semblance analysis technique for air-coupled common midpoint (CMP) measurements with a small antenna offset. The technique was originally developed for seismic surveys, assuming the small spread approximation. Owing to the strong refraction at the surface and shallow investigation depth, this assumption is not valid in the case of air-coupled ground-penetrating radar (GPR). To overcome this assumption, a modification to the method is proposed accounting for the refraction at the surface. Synthetic experiments were executed to demonstrate that the traditional method resulted in a persistent overestimation, whereas the modified method improved the results significantly. Two field experiments have been conducted to test the method under different field conditions. In a first experiment on a road test site, the modified method improved the estimation of depth and propagation velocity significantly. However, the technique failed to estimate the propagation velocity and depth or objects in a second field test, due to rough terrain conditions and noise in the data. Therefore, an additional modification was proposed, by incorporating in-line data as well. This improved the depth and velocity estimations significantly. Overall, this study demonstrates that the traditional velocity semblance analysis (TRAD) is not valid for air-coupled GPR. By accounting for the refraction at the surface and incorporating inline data, it is possible to successfully estimate depth and propagation velocity with small offset air-coupled GPR configurations.

Statistical Methods for the Analysis of Soil Spatial and Temporal Variability

Ahmed Douaik1, Marc van Meirvenne2 and Tibor Toth3,4 1Research Unit on Environment and Conservation of Natural Resources, National Institute of Agricultural Research (INRA), Rabat, 2Department of Soil Management, Ghent University, Ghent, 3Department of Soil Science, Research Institute for Soil Science and Agricultural Chemistry, Budapest, 4Rural, Water and Ecosystem Resources Unit, Institute for Environment and Sustainability, European Commission – Joint Research Center, Ispra 1Morocco 2Belgium 3Hungary 4Italy

Modelling Monnikerede : the topographical reconstruction of a deserted medieval outport near Bruges

The small outport of Monnikerede was part of the portuary system of the later medieval international market of Bruges, which used the Zwin tidal inlet as its gateway to overseas markets. When political, economic and environmental conditions in the Zwin harbours deteriorated, Monnikerede slowly became depopulated and eventually disappeared from the landscape. In order to localise and analyse the morphology of this deserted harbour, an interdisciplinary research scheme was initiated and aimed at integrating historical, cartographic, archaeological and geophysical data. The GIS-based methodology showed that this combination of complementary sources enabled a topographical reconstruction up to the level of individual parcels and allowed for the discernment of social topography. The decline of the city could be visualised through a series of time slices between 1450 and 1850, indicating that Monnikerede’s misfortunes are reflected in the disintegration of the urban fabric. We conclude that integrated research into the available historical and archaeological data can be successful in piecing together the topographical evolution of a now deserted settlement.