erika lück

Rapid multi-scale analysis of near-surface geophysical anomaly maps: Application to an archaeo-geophysical data set

GEOPHYSICS

In near-surface geophysics, ground-based mapping surveys are routinely employed in a variety of a... more In near-surface geophysics, ground-based mapping surveys are routinely employed in a variety of applications including those from archaeology, civil engineering, hydrology, and soil science. The resulting geophysical anomaly maps of, for example, magnetic or electrical parameters are usually interpreted to laterally delineate subsurface structures such as those related to the remains of past human activities, subsurface utilities and other installations, hydrological properties, or different soil types. To ease the interpretation of such data sets, we propose a multi-scale processing, analysis, and visualization strategy. Our approach relies on a discrete redundant wavelet transform (RWT) implemented using cubic-spline filters and the à trous algorithm, which allows to efficiently compute a multi-scale decomposition of 2D data using a series of 1D convolutions. The basic idea of the approach is presented using a synthetic test image, while our archaeo-geophysical case study from Nor...

Determining the within-field yield variability from seasonally changing soil conditions

Precision Agriculture

1D inversion of direct current data acquired with a rolling electrode system

Journal of Applied Geophysics

Testing of multi-coil FDEM sensors on a field model with magnetic susceptibility contrast

ArchéoSciences, 2009

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Comparison of non-destructive geophysical methods to predict the heterogeneity of subsoil compaction

Easy access to regionalise subsoil compaction on the field scale has not yet been realised with c... more Easy access to regionalise subsoil compaction on the field scale has not yet been realised with common soil physical methods. Caused by specific methodical limitation, reproducible results can commonly only be obtained in the laboratory. Existing field methods to access this problem allow simple punctual measurements, but are not adequate for a larger spatial resolution. Non-destructive probes, on the other hand, provide a better spatial resolution but in general do not show directly the state of mechanical stress. A possible solution for this problem is to assess the state of mechanical compaction via the stress-at-rest-coefficient, K0, obtained by mechanical probe measurements in combination with various independently measured geophysical data. Data can easily be assessed with the apparent electrical conductivity (ECa), the electrical resistivity (ER), and electroma- gnetic reflection (GPR). Here we present experiments with a hand driven Penetrologger and the geophysical sensors E...

Measurement of water content at different scales and geostatistical analysis

Accurate measurement of the spatial patterns of water content is an important aspect of most vado... more Accurate measurement of the spatial patterns of water content is an important aspect of most vados zone studies, e.g. ground truthing for remote sensing data-sets, the identification of near surface flow processes, or as initial condition for a hydrological modelling. Water content can be determined, either measuring the temporal dynamics with permanently installed equipment or by high spatial resolution snapshots at the field scale during field campaigns. In the upper Weisseritz in Saxony, Germany, at selected hillslopes with different microtopography and land use the water content was measured with both methods. The study area is characterised by gentle slopes with a rural land use. The soils are dominated by cambisoils. The snapshots were surveyed with soil moisture probes as well as with ground penetrating radar. Continuous measurements were carried out with two Spatial TDR clusters (STDR) with a high spatio-temporal resolution. STDR encompasses three components: (1) a sampling ...

Combined interpretation of multiple geophysical techniques: an archaeological case study

In order to locate and ascertain the dimensions of an ancient orangery, we explored an area of ab... more In order to locate and ascertain the dimensions of an ancient orangery, we explored an area of about 70 m x 60 m in the Rheinsberg Palace Garden (Germany) with multiple geophysical techniques. The Rheinsberg Park, situated about 100 km northwest of Berlin, Germany, was established by the Prussian emperors in the 18th century. Due to redesign of the architecture

Properties of soils from the Swedish long-term fertility experiments: VI. Mapping soil electrical conductivity with different geophysical methods

Acta Agriculturae Scandinavica Section B-soil and Plant Science, 2011

Swedish long-term soil fertility experiments were used to investigate the effect of texture and f... more Swedish long-term soil fertility experiments were used to investigate the effect of texture and fertilization regime on soil electrical conductivity. In one geophysical approach, fields were mapped to characterize the horizontal variability in apparent electrical conductivity down to 1.5 m soil depth using an electromagnetic induction meter (EM38 device). The data obtained were geo-referenced by dGPS. The other approach consisted

Process identification through rejection of model structures in a mid‐mountainous rural catchment: observations of rainfallrunoff response, geophysical conditions …

by Dominik Reusser and erika lück

Hydrological …, 2009

The intention of the presented study is to gain a better understanding of the mechanisms that cau... more

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Prospection of two circular Bronze Age ditches with multi-receiver electrical conductivity sensors (North Belgium)

by erika lück and Jean Bourgeois

Journal of Archaeological Science, 2010

Two types of electrical conductivity sensors were evaluated to prospect circular ditches surround... more Two types of electrical conductivity sensors were evaluated to prospect circular ditches surrounding former Bronze Age burial mounds, complementing aerial photography. The first sensor was based on the electrical resistivity (ER) method, while the second sensor was based on frequency-domain electromagnetic induction (FDEM). Both sensors were designed with multiple receivers, which measure several depth sensitivities simultaneously. First, the sensors were tested on an experimental site where a rectangular structure with limited dimensions was dug in a sandy soil. The structure appeared as a higher conductivity anomaly in the low-conductivity sand. Then, both methods were applied on two Bronze Age sites with different soil properties, which were discovered by aerial photography. The first site, in a sandy soil, gave only very weak anomalies. Soil augering revealed that the ditch filling consisted of the same sandy material as the surrounding, therefore this filling was not able to cause a high-conductivity contrast. Due to its lower sensitivity to noise in the low-conductive range, the ER-sensor produced a more pronounced anomaly than the FDEM-sensor. The second site was located on top of a ridge with a shallow substrate of Tertiary, coastal sediments. The ditch was very clearly visible on the sensor maps as a conductive low. At this location, the soil augering revealed that the ditch was dug through an alternating clay-sand layer and subsequently filled up with silty material from the topsoil. Overall, the shallow receiver separation produced anomalies that were both stronger and that corresponded better to the geometry of the ditches. The other receiver separations provided more information on the natural soil layering, and in the case of the ER-array they could be used to obtain a cross-section of the actual electrical conductivity with 2-D inversion modelling. The results of this study proofed that conductivity sensors can detect Bronze Age ditches, with varying contrast depending on the soil geomorphology. Moreover, the sensor maps combined with soil observations by coring provided insight in the environmental conditions that influence the contrast of the anomalies seen on the aerial photographs and the sensor maps.

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Modeling of Wave Dispersion Using Continuous Wavelet Transforms II: Wavelet-based Frequency-velocity Analysis

Pure and Applied Geophysics, 2008

In this paper, we show how to estimate the phase velocities of multi-mode signals as present in 2... more In this paper, we show how to estimate the phase velocities of multi-mode signals as present in 2-D shallow seismic surveys along a seismic line with the help of a method that is based on the deformation of the wavelet spectra of the seismic traces. In analogy with frequency-wavenumber (f–k) analysis, we perform “frequency-velocity” analysis using the correlations between phases of the wavelet spectra. Our method has two tuning parameters — the parameter of an analyzing wavelet and the parameter of a threshold operation. Numerical and experimental examples are presented to illustrate how the method accurately extracts the phase velocity from single- and multi-mode signals.

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Characterization of dispersive surface waves using continuous wavelet transforms

Geophysical Journal International, 2005

In this paper, we propose a method of surface waves characterization based on the deformation of ... more In this paper, we propose a method of surface waves characterization based on the deformation of the wavelet transform of the analysed signal. An estimate of the phase velocity (the group velocity) and the attenuation coefficient is carried out using a model-based approach to determine the propagation operator in the wavelet domain, which depends nonlinearly on a set of unknown parameters. These parameters explicitly define the phase velocity, the group velocity and the attenuation. Under the assumption that the difference between waveforms observed at a couple of stations is solely due to the dispersion characteristics and the intrinsic attenuation of the medium, we then seek to find the set of unknown parameters of this model. Finding the model parameters turns out to be that of an optimization problem, which is solved through the minimization of an appropriately defined cost function. We show that, unlike time-frequency methods that exploit only the square modulus of the transform, we can achieve a complete characterization of surface waves in a dispersive and attenuating medium. Using both synthetic examples and experimental data, we also show that it is in principle possible to separate different modes in both the time domain and the frequency domain.

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Some results of deep seismic investigations in East Germany

Physics of The Earth and Planetary Interiors, 1992

. Some results of deep seismic investigations in East Germany. Phys. Earth Planet. Inter., 69: 23... more . Some results of deep seismic investigations in East Germany. Phys. Earth Planet. Inter., 69: 231-238. In recent years, several deep seismic investigations have been carried Out in the central and southern part of East Germany. In the present paper, the results for P-wave velocity distributions are shown and discussed. Some typical crustal features, such as low-velocity layers, were found in some cases. The Moho was found to ascend from the SE towards the NW, with some interruptions. For several profiles, the S-wave arrivals also were interpreted. The simultaneous evaluation of P-and S-wave velocities were used to obtain information on the behaviour of the elastic parameters A and~, respectively. The seismic models discussed in the present paper have been confirmed by modelling the gravity field, and the results have been published elsewhere. 0031-9201/92/$05.OO

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Prospection of two circular Bronze Age ditches with multi-receiver electrical conductivity sensors (North Belgium

Journal of Archaeological Science, 2010

Two types of electrical conductivity sensors were evaluated to prospect circular ditches surround... more Two types of electrical conductivity sensors were evaluated to prospect circular ditches surrounding former Bronze Age burial mounds, complementing aerial photography. The first sensor was based on the electrical resistivity (ER) method, while the second sensor was based on frequency-domain electromagnetic induction (FDEM). Both sensors were designed with multiple receivers, which measure several depth sensitivities simultaneously. First, the sensors were tested on an experimental site where a rectangular structure with limited dimensions was dug in a sandy soil. The structure appeared as a higher conductivity anomaly in the low-conductivity sand. Then, both methods were applied on two Bronze Age sites with different soil properties, which were discovered by aerial photography. The first site, in a sandy soil, gave only very weak anomalies. Soil augering revealed that the ditch filling consisted of the same sandy material as the surrounding, therefore this filling was not able to cause a high-conductivity contrast. Due to its lower sensitivity to noise in the low-conductive range, the ER-sensor produced a more pronounced anomaly than the FDEM-sensor. The second site was located on top of a ridge with a shallow substrate of Tertiary, coastal sediments. The ditch was very clearly visible on the sensor maps as a conductive low. At this location, the soil augering revealed that the ditch was dug through an alternating clay-sand layer and subsequently filled up with silty material from the topsoil. Overall, the shallow receiver separation produced anomalies that were both stronger and that corresponded better to the geometry of the ditches. The other receiver separations provided more information on the natural soil layering, and in the case of the ER-array they could be used to obtain a cross-section of the actual electrical conductivity with 2-D inversion modelling. The results of this study proofed that conductivity sensors can detect Bronze Age ditches, with varying contrast depending on the soil geomorphology. Moreover, the sensor maps combined with soil observations by coring provided insight in the environmental conditions that influence the contrast of the anomalies seen on the aerial photographs and the sensor maps.

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Sensitivity of multi-coil frequency domain electromagnetic induction sensors to map soil magnetic susceptibility

European Journal of Soil Science, 2010

Magnetic susceptibility is an important indicator of anthropogenic disturbance in the natural soi... more Magnetic susceptibility is an important indicator of anthropogenic disturbance in the natural soil. This property is often mapped with magnetic gradiometers in archaeological prospection studies. It is also detected with frequency domain electromagnetic induction (FDEM) sensors, which have the advantage that they can simultaneously measure the electrical conductivity. The detection level of FDEM sensors for magnetic structures is very dependent on the coil configuration. Apart from theoretical modelling studies, a thorough investigation with field models has not been conducted until now. Therefore, the goal of this study was to test multiple coil configurations on a test field with naturally enhanced magnetic susceptibility in the topsoil and with different types of structures mimicking real archaeological features. Two FDEM sensors were used with coil separations between 0.5 and 2 m and with three coil orientations. First, a vertical sounding was conducted over the undisturbed soil to test the validity of a theoretical layered model, which can be used to infer the depth sensitivity of the coil configurations. The modelled sounding values corresponded well with the measured data, which means that the theoretical models are applicable to layered soils. Second, magnetic structures were buried in the site and the resulting anomalies measured to a very high resolution. The results showed remarkable differences in amplitude and complexity between the responses of the coil configurations. The 2-m horizontal coplanar and 1.1-m perpendicular coil configurations produced the clearest anomalies and resembled best a gradiometer measurement.

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Potentials and constraints of different types of soil moisture observations for flood simulations in headwater catchments

Natural Hazards

Flood generation in mountainous headwater catchments is governed by rainfall intensities, by the ... more Flood generation in mountainous headwater catchments is governed by rainfall intensities, by the spatial distribution of rainfall and by the state of the catchment prior to the rainfall, e.g. by the spatial pattern of the soil moisture, groundwater conditions and possibly snow. The work presented here explores the limits and potentials of measuring soil moisture with different methods and in different scales and their potential use for flood simulation. These measurements were obtained in 2007 and 2008 within a comprehensive multi-scale experiment in the Weisseritz headwater catchment in the Ore-Mountains, Germany. The following technologies have been applied jointly thermogravimetric method, frequency domain reflectometry (FDR) sensors, spatial time domain reflectometry (STDR) cluster, ground-penetrating radar (GPR), airborne polarimetric synthetic aperture radar (polarimetric SAR) and advanced synthetic aperture radar (ASAR) based on the satellite Envisat. We present exemplary soil measurement results, with spatial scales ranging from point scale, via hillslope and field scale, to the catchment scale. Only the spatial TDR cluster was able to record continuous data. The other methods are limited to the date of over-flights (airplane and satellite) or measurement campaigns on the ground. For possible use in flood simulation, the observation of soil moisture at multiple scales has to be combined with suitable hydrological modelling, using the hydrological model WaSiM-ETH. Therefore, several simulation experiments have been conducted in order to test both the usability of the recorded soil moisture data and the suitability of a distributed hydrological model to make use of this information. The measurement results show that airborne-based and satellite-based systems in particular provide information on the near-surface spatial distribution. However, there are still a variety of limitations, such as the need for parallel ground measurements (Envisat ASAR), uncertainties in polarimetric decomposition techniques (polarimetric SAR), very limited information from remote sensing methods about vegetated surfaces and the non-availability of continuous measurements. The model experiments showed the importance of soil moisture as an initial condition for physically based flood modelling. However, the observed moisture data reflect the surface or near-surface soil moisture only. Hence, only saturated overland flow might be related to these data. Other flood generation processes influenced by catchment wetness in the subsurface such as subsurface storm flow or quick groundwater drainage cannot be assessed by these data. One has to acknowledge that, in spite of innovative measuring techniques on all spatial scales, soil moisture data for entire vegetated catchments are still today not operationally available. Therefore, observations of soil moisture should primarily be used to improve the quality of continuous, distributed hydrological catchment models that simulate the spatial distribution of moisture internally. Thus, when and where soil moisture data are available, they should be compared with their simulated equivalents in order to improve the parameter estimates and possibly the structure of the hydrological model.

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Process identification through rejection of model structures in a mid-mountainous rural catchment: observations of rainfall-runoff response, geophysical conditions and model inter-comparison

Hydrological Processes, 2009

The intention of the presented study is to gain a better understanding of the mechanisms that cau... more The intention of the presented study is to gain a better understanding of the mechanisms that caused the bimodal rainfall-runoff responses which occurred up to the mid-1970s regularly in the Schäfertal catchment and vanished after the onset of mining activities. Understanding this process is a first step to understanding the ongoing hydrological change in this area. It is hypothesized that either subsurface stormflow, or fast displacement of groundwater could cause the second delayed peak. A top-down analysis of rainfall-runoff data, field observations as well as process modelling are combined within a rejectionistic framework. A statistical analysis is used to test whether different predictors, which characterize the forcing, near surface water content and deeper subsurface store, allow the prediction of the type of rainfall-runoff response. Regression analysis is used with generalized linear models as they can deal with non-Gaussian error distributions as well as a non-stationary variance. The analysis reveals that the dominant predictors are the pre-event discharge (proxy of state of the groundwater store) and the precipitation amount. In the field campaign, the subsurface at a representative hillslope was investigated by means of electrical resistivity tomography in order to identify possible strata as flow paths for subsurface stormflow. A low resistivity in approximately 4 m depth-either due to a less permeable layer or the groundwater surface-was detected. The former could serve as a flow path for subsurface stormflow. Finally, the physical-based hydrological model CATFLOW and the groundwater model FEFLOW are compared with respect to their ability to reproduce the bimodal runoff responses. The groundwater model is able to reproduce the observations, although it uses only an abstract representation of the hillslopes. Process model analysis as well as statistical analysis strongly suggest that fast displacement of groundwater is the dominant process underlying the bimodal runoff reactions.

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Resistivity mapping with GEOPHILUS ELECTRICUS – information about lateral and vertical soil heterogeneity

GEOPHILUS is a novel system for mapping complex electrical bulk resistivity of soil with rolling ... more GEOPHILUS is a novel system for mapping complex electrical bulk resistivity of soil with rolling electrodes. Amplitude and phase data are measured simultaneously for four frequencies within a range between 1 mHz and 1 kHz. The sensor design and its technical specification allow measuring the electrical parameters at five depth levels up to 1.5 m depth. Using DGPS for positioning and a suitable cross-country vehicle, it is possible to map about 100 ha/day recording 1 data point per second and 18 m line spacing.

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