estimation of permeable pathways and water content using tomographic radar data near surface environmental investigations often require monitoring of the spatial distribution of water content and identification of preferential fluid flow paths water content estimates are needed for example to model and predict pollutant transport through the vadose zone and to subsequently design an efficient and reliable remediation plan the characteristics of preferential flow paths as well as the location and geometry of these features are necessary to model and predict flow and transport in complex geological media such as fractured or strongly heterogeneous porous systems

high resolution characterization of vadose zone dynamics using cross borehole radar characterization of the dynamics of moisture migration in the unsaturated zone of aquifers is essential if reliable estimates of the transport of pollutants threatening such aquifers are to be made electrical geophysical investigation techniques such as ground penetrating radar offer suitable methods for monitoring moisture content changes in the vadose zone moreover these tools permit relatively large measurement scales appropriate for hydrological models of unsaturated processes and thus they offer a distinct advantage over conventional measurement approaches ground penetrating radar when applied in transmission mode between boreholes can provide high resolution information on lithological and hydrological features the technique may be applied in tomographic mode and in a much simpler vertical profile mode both modes of measurement have been utilized using two boreholes 5 m apart located at a field site in the uk sherwood sandstone aquifer radar transmission measurements have been used to characterize the change in moisture content in unsaturated sandstone due to controlled water tracer injection continual monitoring of cross borehole radar measurements over an 18 month period has also permitted determination of travel times of natural loading to the system and has revealed the impact of subtle contrasts in lithology on changes in moisture content over time the time series of inferred moisture contents show clearly wetting and drying fronts migrating at a rate of approximately 2 m month 1 throughout the sandstone

radar frequency dielectric dispersion in sandstone implications for determination of moisture and clay content 1 the relationship between dielectric permittivity water saturation and clay content for the sherwood sandstone from ne england was characterized as part of a wider study of the vadose zone moisture dynamics and pollution vulnerability of this aquifer dielectric permittivity was measured over the full range of saturation levels for various lithologies ranging from clean medium grained sandstone to fine grained sandstone containing up to 5 clay using a specially constructed dielectric cell dielectric constant kr is largely independent of frequency between 350 mhz and 1000 mhz below 350 mhz kr of fine grained clay rich sandstone shows frequency dispersion tests on physical models of the sandstone consisting of a fine fraction of ottawa sand and montmorillonite clay indicate that the clay minerals within the sandstone are responsible for its frequency dispersive behavior these tests also show that increasing pore fluid salinity increases dielectric dispersion at the lower end of the frequency range which indicates that this arises from the interfacial maxwell wagner mechanism associated with platy clay particles water saturated sand clay mixtures show very low dielectric constants at high frequencies over 650 mhz this effect is independent of salinity and probably results from the layered geometric arrangement of solids bound and free water within the swelling clay the complex refractive index method crim with a mineral dielectric constant of about 5 provides a good match to the water saturation versus dielectric constant data for all sherwood sandstone lithologies at frequencies between 350 and 1000 mhz and for clay poor sandstone at lower frequencies below 350 mhz the presence of a few percent of clay in some sherwood sandstone lithologies raises their crim best fit mineral dielectric constant substantially

resistivity and percolation study of preferential flow in vadose zone at bokhorst germany traditional nondestructive resistivity techniques have been applied in combination with tracer displacement and conventional soil moisture recording methods i e buried tensiometer and time domain reflectometry tdr for studying flow processes at an arable site in bokhorst germany three water infiltration experiments were carried out using tap water spiked with a nonreactive tracer at different concentrations the study aimed at exploring the capabilities of these combined techniques for tracing the preferential movement of water in the uppermost 1 5 m of the highly heterogeneous vadose zone the results illustrate that the applied tensiometer and tdr techniques can detect the relatively fast flow process at their position points and thus only tentatively trace the preferential flow the additional application of the resistivity method can trace the preferential flow paths continuously along the plane of measurements the results of the individual applied methods complement and confirm each other

estimating vadose zone hydraulic properties using ground penetrating radar the impact of prior information 1 a number of geophysical methods such as ground penetrating radar gpr have the potential to provide valuable information on hydrological properties in the unsaturated zone in particular the stochastic inversion of such data within a coupled geophysical hydrological framework may allow for the effective estimation of vadose zone hydraulic parameters and their corresponding uncertainties a critical issue in stochastic inversion is choosing prior parameter probability distributions from which potential model configurations are drawn and tested against observed data a well chosen prior should reflect as honestly as possible the initial state of knowledge regarding the parameters and be neither overly specific nor too conservative in a bayesian context combining the prior with available data yields a posterior state of knowledge about the parameters which can then be used statistically for predictions and risk assessment here we investigate the influence of prior information regarding the van genuchten mualem vgm parameters which describe vadose zone hydraulic properties on the stochastic inversion of crosshole gpr data collected under steady state natural loading conditions we do this using a bayesian markov chain monte carlo mcmc inversion approach considering first noninformative uniform prior distributions and then more informative priors derived from soil property databases for the informative priors we further explore the effect of including information regarding parameter correlation analysis of both synthetic and field data indicates that the geophysical data alone contain valuable information regarding the vgm parameters however significantly better results are obtained when we combine these data with a realistic informative prior

characterization of the porosity distribution in the upper part of the karst biscayne aquifer using common offset ground penetrating radar everglades national park florida summary the karst biscayne aquifer is characterized by a heterogeneous spatial arrangement of porosity and hydraulic conductivity making conceptualization difficult the biscayne aquifer is the primary source of drinking water for millions of people in south florida thus information concerning the distribution of karst features that concentrate the groundwater flow and affect contaminant transport is critical the principal purpose of the study was to investigate the ability of two dimensional ground penetrating radar gpr to rapidly characterize porosity variability in the karst biscayne aquifer in south florida an 800 m long gpr transect of a previously investigated area at the long pine key nature trail in everglades national park collected in fast acquisition common offset mode shows hundreds of diffraction hyperbolae the distribution of diffraction hyperbolae was used to estimate electromagnetic em wave velocity at each diffraction location and to assess both horizontal and vertical changes in velocity within the transect a petrophysical model complex refractive index model or crim was used to estimate total bulk porosity a set of common midpoint surveys at selected locations distributed along the common offset transect also were collected for comparison with the common offsets and were used to constrain one dimensional 1 d distributions of porosity with depth porosity values for the saturated miami limestone ranged between 25 and 41 for common offset gpr surveys and between 23 and 39 for common midpoint gpr surveys laboratory measurements of porosity in five whole core samples from the saturated part of the aquifer in the study area ranged between 7 1 and 41 8 gpr estimates of porosity were found to be valid only under saturated conditions other limitations are related to the vertical resolution of the gpr signal and the volume of the material considered by the measurement methodology overall good correspondence between gpr estimates and the direct porosity values from the whole core samples confirms the ability of gpr common offset surveys to provide rapid characterization of porosity variability in the biscayne aquifer the common offset survey method has several advantages 1 improved time efficiency in comparison to other gpr acquisition modes such as common midpoints and 2 enhanced lateral continuity of porosity estimates particularly when compared to porosity measurements on 1 d samples such as rock cores the results also support the presence of areas of low em wave velocity or high porosity under saturated conditions causing velocity pull down areas and apparent sag features in the reflection record this study shows that gpr can be a useful tool for improving understanding of the petrophysical properties of highly heterogeneous systems such as karst aquifers and thus may assist with the development of more accurate groundwater flow models such as those used for restoration efforts in the everglades

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

borehole time domain reflectometry in layered sandstone impact of measurement technique on vadose zone process identification the hydraulic behaviour of the vadose zone of a layered sandstone aquifer has been investigated using borehole based time domain reflectometry tdr both a commercially available portable packer tdr system trime b3l borehole packer probe and specially designed borehole emplaced tdr probes were used to monitor seasonal fluctuations in water content in the vadose zone of a layered sandstone over 1 year under natural rainfall loading the data show that the vadose zone contains seasonal perched water tables that form when downward percolating water reaches layers of fine grained sandstone and siltstone and causes local saturation the formation of perched water tables is likely to lead to lateral flow bypassing the less permeable finer layers this contrasts with behaviour inferred from previous studies of the same aquifer that used borehole radar and resistivity which suggested its vadose zone behaviour was characterized by uniform downwards migration of wetting fronts to investigate the impact of measurement technique on observed response the tdr data reported here were used to produce simulated zero offset profile zop borehole radar responses this simulation confirmed the limited ability of zop borehole radar to detect key vadose zone processes because the phenomenon of critical refraction minimizes the sensitivity of the results to high water content layers the ability of the resistivity method to detect perched water table responses is also limited because of the relatively large sampling volume of the technique the study illustrates that inappropriate technique selection results in hydrological process mis identification with serious consequences for the usefulness of data in hydrological modeling

ground penetrating radar for determining volumetric soil water content results of comparative measurements at two test sites ground penetrating radar gpr can provide information on the soil water content of the unsaturated zone in sandy deposits via measurements from the surface and so avoids drilling proof of this was found from measurements of radar wave velocities carried out ten times over 13 months at two test sites in the netherlands at these same locations and on the same dates soil water content was measured in access robes using a capacitance probe comparison of gpr and capacitance probe observations revealed that 1 the inferred absolute values of soil water content agree well this is remarkable because the soil water content is deduced entirely differently for the two methods 2 seasonal fluctuations in soil water content established for different general depth zones of radar waves correlate well with the fluctuations observed in the access tubes 3 the various methods to determine the propagation velocities of radar waves are complementary together they produce a realistic and reasonably complete image of the vertical distribution of the soil water content of the entire unsaturated zone high frequency 200 mhz direct groundwaves and refracted waves constitute a particularly attractive complementary combination which provides information on consecutive shallow zones in the underground i e the zones of major soil water content fluctuations 4 lateral variations established at one of the test sites where several access tubes have been placed in a transect also follow from the gpr measurements along that profile this non destructive determination of soil water content in practically continuous and detailed sections is one of the great assets of gpr opening the way to mapping preferential soil water flow paths

efficient three dimensional data inversion soil characterization and moisture monitoring from cross well ground penetrating radar at a vermont test site we extend our methodology for three dimensional parameter structure and value estimation and apply it to a vermont test site ground penetrating radar gpr cross well travel times are inverted for estimation of heterogeneous gpr soil velocities before and after a controlled release of salt water in the unsaturated zone the method which is based on an approximation of the extended kaiman filter in conjunction with data driven zonation automatically estimates not only distributed zone values but also the number of zones zone geometry and zone covariance resultant gpr velocity estimates are shown to reduce travel time estimation errors and to be consistent with independent cone penetrometer measurements at all five walls at the site comparison of velocity estimates before and after forced injection of salt water is used to detect and visualize soil moisture patterns in three dimensions by varying the cluster tolerance criterion in the data driven zonation process the user can obtain a desired resolution of heterogeneity number of zones used in the resultant model

quantitative imaging of solute transport in an unsaturated and undisturbed soil monolith with 3 d ert and tdr electrical resistivity tomography ert has proved to be a valuable tool for imaging solute transport processes in the subsurface however a quantitative interpretation of corresponding ert results is constrained by a number of factors one such factor is the nonuniqueness of the ert inverse problem if no additional constraints are imposed in the vadose zone further problems arise from the general ambiguity of the imaged bulk electrical conductivity in terms of water content and solute concentration in this study we address these issues in detail for a solute tracer experiment conducted in an undisturbed unsaturated soil monolith where the tracer transport was monitored by means of 3 d smoothness constrained ert and time domain reflectometry tdr measurements the experimental design allowed the determination of solute tracer concentrations directly from imaged bulk electrical conductivity independent tdr data and effluent tracer concentrations provided a ground truth for the ert derived apparent convection dispersion equation transport parameters the apparent transport velocity calculated from the ert results was consistent with that based on tdr data and the sampled effluent independent of the degree of smoothness imposed in the ert inversion on the other hand the apparent dispersivity calculated from the ert results was larger than that estimated from tdr data but smaller than that estimated from the sampled effluent with the magnitude of deviations dependent on the degree of smoothing importantly no mass balance problems were observed in the ert results we believe that this is largely a consequence of the uniform application of the tracer as a front and of the configuration of the electrode array with respect to the main transport direction in conclusion the study demonstrates that ert can yield unprecedented quantitative information about local and column scale solute transport characteristics in natural soils

electrical properties of partially saturated sandstones novel computational approach with hydrogeophysical applications 1 electric and electromagnetic geophysical tools are suitable methods for investigating moisture content transport and storage properties of the subsoil with noninvasive surveys interpretation of field data is still based on empirical or semiempirical equations which must be calibrated with complex time consuming laboratory measurements in this paper we develop pore scale models suitable for computing the effective electric conductivity and the effective permittivity of partially saturated porous media on the basis of simple structural parameters grain size distribution and porosity we compute the electrical conductivity with three approaches that model the conductivity of the shell of coating clay around solid grains of shaly sandstones using different assumptions we compare the simulated results with experimental data from sherwood sandstone uk and discuss the effect of these assumptions on the effective conductivity simulations performed using a modeling approach that accounts for interaction between volume and surface conduction show an excellent agreement with experimental data we also model the effective permittivity of the same porous medium at several saturation values and obtain a good match with laboratory measurements

a theoretical treatment of the effect of microscopic fluid distribution on the dielectric properties of partially saturated rocks1 microscopic fluid distribution can have a significant effect on the dielectric properties of partially saturated rocks evidence of this effect is found in the laboratory data presented by knight and nur in which different methods for controlling saturation produced very different results for the dependence of the dielectric response on water saturation in this study previously derived models for the dielectric response of a heterogeneous medium are generalized and the case of a pore space occupied by multiple pore fluids is considered by using various geometrical distributions of water and gas it is observed that both the pore geometry in which saturation conditions are changing and the gas water geometry within a given pore space are critical factors in determining the effective dielectric response of a partially saturated rock as an example data for a tight gas sandstone undergoing a cycle of imbibition and drying are analysed previous research has demonstrated that significantly different microscopic fluid distributions result from the application of these two techniques to control the level of water saturation by approximating these microscopic fluid distributions using simple geometrical models good agreement is found between experimental data and calculated dielectric properties

variations in free phase gases in peat landforms determined by ground penetrating radar 1 the spatial variability of biogenic gas produced by methanogenic archaea is difficult to assess within saturated peat soils and is often poorly quantified this study uses ground penetrating radar to noninvasively estimate the vertical distribution of biogenic free phase gas fpg in two distinct peat landform types in the glacial lake agassiz peatland minnesota a near crest bog and a midslope lawn i e both as defined by surface vegetation communities ground penetrating radar velocities retrieved from common midpoint surveys were modeled using the complex refractive index model to estimate free phase gas volumes along one dimensional vertical profiles near crest bog landforms are characterized by vertical variability in gas content with accumulations along the peat column up to 24 by volume of fpg localized within the deep peat e g 2 4 m depth midslope lawn sites show lower total volumes up to 12 free phase gas and less variability that result in a more even free phase gas distribution throughout the vertical profile high resolution data also suggests the presence of thinner layers 1 m containing up to 40 free phase gas at a near crest site our results suggest that spatial distribution of free phase gas along the peat column may vary in the glacial lake agassiz peatlands depending on peat landform statistical analysis supports vertical variability of ground penetrating radar velocity data with a 95 confidence limit our results could potentially be upscaled using surface vegetation communities to estimate landscape scale gas storage potential in peat landforms

estimating porosity and solid dielectric permittivity in the miami limestone using high frequency ground penetrating radar gpr measurements at the laboratory scale subsurface water flow in south florida is largely controlled by the heterogeneous nature of the karst limestone in the biscayne aquifer and its upper formation the miami limestone these heterogeneities are amplified by dissolution structures that induce changes in the aquifer s material and physical properties i e porosity and dielectric permittivity and create preferential flow paths understanding such patterns are critical for the development of realistic groundwater flow models particularly in the everglades where restoration of hydrological conditions is intended in this work we used noninvasive ground penetrating radar gpr to estimate the spatial variability in porosity and the dielectric permittivity of the solid phase of the limestone at centimeter scale resolution to evaluate the potential for field based gpr studies a laboratory setup that included high frequency gpr measurements under completely unsaturated and saturated conditions was used to estimate changes in electromagnetic wave velocity through miami limestone samples the complex refractive index model was used to derive estimates of porosity and dielectric permittivity of the solid phase of the limestone porosity estimates of the samples ranged between 45 2 and 66 0 and showed good correspondence with estimates of porosity using analytical and digital image techniques solid dielectric permittivity values ranged between 7 0 and 13 0 this study shows the ability of gpr to image the spatial variability of porosity and dielectric permittivity in the miami limestone and shows potential for expanding these results to larger scales and other karst aquifers

effective permittivity of porous media a critical analysis of the complex refractive index model the availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods this study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials a number of empirical semi empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content one such relationship named complex refractive index model or lichteneker rother model has been extensively applied in recent years here we first analyse the characteristics of this lichteneker rother model by means of theoretical considerations this theoretical analysis indicates that the lichteneker rother exponent is dependent upon the geometrical properties of the porous structure as well as the permittivity contrast between the different phases pore scale modelling and experimental data further support this result the parameter estimation robustness in presence of synthetic data error is also assessed this demonstrates that lichteneker rother parameters cannot in general be independently identified on the basis of bulk dielectric constant versus moisture content data

delineation of macroporous zones in the unsaturated portion of the miami limestone using ground penetrating radar miami dade county florida summary the atlantic coastal ridge in dade county is an ooid shoal formed during the late pleistocene the ridge is composed of the eogenetic karst miami limestone characterized by a heterogeneous distribution of porosity that can manifest as large touching vug macroporous features with sizes in the meters and tens of meters direct evidence for the presence of such large dissolution features is only visible when exposed to the surface which may be problematic in urbanized areas for that reason it is critical to detect any potential precursors for such dissolution features at the subsurface level the purpose of this study was to investigate the ability of ground penetrating radar to detect areas of macroporosity by quantifying changes in electromagnetic wave velocity and relate them to changes in porosity after application of the complex refractive index model crim in order to constrain volumetric water content vwc in the crim an experiment using miami limestone samples was designed to understand 1 the range of typical vwcs and 2 the effect of capillary fringe on water table elevation the results show several areas where increases in em wave travel time associated with contrasts in porosity exceeding 40 cannot be explained by changes in vwcs typically shown in the miami limestone this study may help understand porosity variability in the unsaturated part of the miami limestone and if expanded to larger scales may aid groundwater flow models by better capturing distributions of macroporous areas that may contribute to direct recharge of the biscayne aquifer

the mortagne granite pluton france emplaced by pull apart along a shear zone structural and gravimetric arguments and regional implication the emplacement mechanism and kinematics and the 3 d geometry of the variscan granite pluton of mortagne are interpreted using systematic measurements of the granite structure allied with micro structural observations from a detailed gravimetric study it is proposed that magma infilled a pull apart structure which formed along a jog of a northwest southeast trending sinistral zone of shear a second episode of shearing under a dextral regime and independent of emplacement was responsible for perigranitic tectonites these successive transcurrent opposite movements already documented for variscan times in western france are discussed concerning the age of the mortagne pluton 313 15 m y

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

nonparametric description of peak acceleration as a function of magnitude distance and site in guerrero mexico this article describes the peak accelerations observed on a network of strong motion accelerographs above the subduction zone in guerrero mexico as a function of magnitude and hypocentral distance our empirical description differs from regression analysis however in that it produces a table of values of peak acceleration for selected values of m and r and an interpolation rule to obtain peak acceleration at intermediate values with this approach the existence and extent of saturation of peak acceleration as magnitude increases is dictated by the data and unlimited flexibility is allowed in the distance dependence of the peak acceleration this nonparametric approach does not allow extrapolation beyond the range of the data and is thus most useful when the data spans a large magnitude and distance range after 7 yr of recording the digital guerrero accelerograph network has obtained enough data to test the concept the records include events with magnitudes ranging from under 3 to 8 1 with all magnitudes recorded at distances ranging from nearly directly above the rupture to distances where acceleration has become too small to trigger the instruments the data used in this study consist of 528 recordings each three components from 146 earthquakes that occurred between 1985 and 1990 all but one station are on rock sites since all the accelerograms are recorded by one of 30 stations there is an average of about 18 records for each station the results suggest that at short distances about 14 to 25 km from the fault as magnitude increases the peak horizontal acceleration saturates at about 20 g however unlike small earthquakes peak accelerations decrease very slowly with increased distance from the rupture in a large magnitude station corrections for peak acceleration reduced the rms misfit by about 15 for the horizontal component by 12 for the vertical component and by 21 for the ratio for some stations horizontal corrections are close to vertical corrections but others show very different site effects on horizonal and vertical components the ratios of peak vertical acceleration to peak horizontal acceleration show a very weak tendency to decrease as magnitude increases and this tendency is further reduced at most distances after correction for average site effects the average value of this ratio is 0 70 before the station correction after these corrections for 55 events with known stress drop the residual between the predicted peak acceleration and the observed peak acceleration is correlated with stress drop although scattered the observations are consistent with a theoretical prediction that amax 0 80

evolution of biogenic gases in peat blocks inferred from noninvasive dielectric permittivity measurements 1 peatlands contain methanogenic archea responsible for generating significant amounts of free phase biogenic gases for example methane and carbon dioxide but considerable uncertainty still exists regarding the mechanisms of formation and spatial distribution of these gases within the soil matrix we demonstrate the effectiveness of a new method to record noninvasively the evolution spatial distribution and emission patterns of biogenic gases in a peat soil a peat block 0 022 m3 was extracted from a large freshwater peatland in maine the bulk dielectric permittivity at 1 2 ghz for multiple slices of the block was measured noninvasively 1 as temperature was increased 2 c d 1 from 5 c to 21 c and 2 for a subsequent 2 month period during which temperature was held constant at 21 1 c methane emissions at the surface and peat surface deformation were monitored concurrently using a portable methane detector and a grid of surface elevation rods respectively our results demonstrate that 1 the measurement of electromagnetic wave traveltimes across a peat block offers a unique and more accurate when compared to surface deformation measurements way to monitor gasdynamics and spatial gas distribution within a peat block without any disturbance to the natural gas regime 2 the ebullition under our experimental conditions seems to preferentially occur from the near surface peat and shows some correspondence with changes in atmospheric pressure and 3 the ebullition flux exhibits periodicity suggesting that it may be predictable and quantifiable which could assist climate modeling efforts our findings are consistent with previous studies based on gasdynamics in peat soils including gas volumes and fluxes associated with biogenic gas ebullition

ground penetrating radar as a tool to detect rock heterogeneities channels cemented layers and fractures in the luxembourg sandstone formation grand duchy of luxembourg a combined study of radar profiles and thin section analysis supported by modelling of synthetic radar traces reveals that ground penetrating radar gpr reflections generated in diagenetically altered sandstones cannot always be interpreted unequivocally this is illustrated in the luxembourg sandstone formation which has been altered diagenetically by selective carbonate cementation and fracturing cemented lenses and concretions developed along the bedding planes especially at places with high primary carbonate content cementation resulted in the alternation of cemented carbonate rich sandy layers thickness 30 50 cm and variable length and uncemented carbonate poor sandstone layers the ability of gpr to detect the geometry of these lenses and vertical fractures with centimetre apertures has been tested at several antenna frequencies 100 200 250 and 500 mhz relative dielectric permittivity calculations were carried out to assess variations of this electric property within the cemented and uncemented layers as a function of porosity calcite and water content in the pores two dimensional full waveform modelling was also carried out to study the effect of conductivity in the sandstones and the effect of interlayer clay seams at the penetration depth of the radar 7 m with 250 mhz cemented lenses and concretions could only be detected with gpr when the porosity contrast was sufficiently high which is not always the case this conclusion is supported by the modelling the data also proved the ability of radar to detect large open vertical fractures along which sandstones are weathered the study has implications for investigations which will use gpr to detect three dimensional distribution of diagenetic pore filling precipitates as well as secondary porosity development along fractures

effect of soil roughness on the inversion of off ground monostatic gpr signal for noninvasive quantification of soil properties we report on a laboratory experiment that investigates the effect of soil surface roughness on the identification of the soil electromagnetic properties from full wave inversion of ground penetrating radar gpr data in the frequency domain the gpr system consists of an ultrawide band stepped frequency continuous wave radar combined with an off ground monostatic horn antenna radar measurements were performed above a rectangular container filled with a loose sandy soil subject to seven water contents and four random surface roughnesses including a smooth surface as reference compared to previous studies we have reduced the modeling error of the gpr signal for the smooth surface case thanks to improved antenna transfer functions by solving an overdetermined system of equations based on six model configurations instead of only three then the continuously increasing effect of surface roughness on the radar signal with respect to frequency is clearly observed in close accordance with rayleigh s criterion both the radar signal and the inversely estimated parameters are not significantly affected if the surface protuberances are smaller than one eighth of a wavelength in addition when this criterion is not respected errors are made in the estimated parameters but the inverse solution remains stable this demonstrates the promising perspectives for application of gpr for noninvasive water content estimation in agricultural and environmental field applications

seasonal variation of moisture content in unsaturated sandstone inferred from borehole radar and resistivity profiles understanding the processes controlling recharge to aquifers is critical if accurate predictions are to be made on the fate of contaminants in the subsurface environment in order to understand fully the hydrochemical mechanisms in the vadose zone it is essential that the dynamics of the hydrology can be suitably characterised the correlation between moisture content and both bulk dielectric and resistivity properties of porous media is well established using suitably placed sensors in boreholes detailed depth profiles of dielectric and resistivity behaviour have been monitored over a period of two years at a triassic sherwood sandstone aquifer field site at hatfield england the borehole borehole transmission radar and borehole resistivity profiles show a significant correlation through appropriate petrophysical relationships derived from core samples seasonal dynamics of the vadose zone are seen to illustrate the migration of wetting and drying fronts over the monitoring period at a second field site in eggborough located 17 km from hatfield similar temporal changes in moisture content in the sandstone were observed using borehole radar profiles travel times of seasonal wetting fronts through the sandstone at both sites appear to be approximately 2 m per month the retardation of this front propagation in the top 3 m is also common to both sites suggesting that pollutant transport may be principally controlled by near surface sediments the results have important consequences to existing groundwater modelling programmes that are being utilised to predict transfer of agricultural chemicals through the vadose zone

application of time domain reflectometry to determination of volumetric water content in rock time domain reflectometry tdr is a widely used technique for measuring soil water content to examine its applicability to rock the authors applied tdr to a variety of rocks in the laboratory the obtained relationships between the apparent dielectric constant and the volumetric water content showed a behavior that can be partly explained by the effect of gaps between the tdr probe and rock for rocks with an effective porosity smaller than that of soil the well known model presented by topp et al 1980 for soil tended to overestimate the water content for such rocks it was determined that an individual calibration was needed for accurate determination of water content if no experimental calibration is possible frequently used mixing models may be used to establish the calibration function our investigations suggest that tdr showed the potential for measuring the apparent dielectric constant of rock and further for determining water content in rock

velocity variations and water content estimated from multi offset ground penetrating radar the common midpoint cmp processing technique has been shown to be effective in improving the results of ground penetrating radar gpr profiling when radar data are collected with the cmp multioffset geometry stacking increases the signal to noise ratio of subsurface radar reflections and results in an improved subsurface image an important aspect of cmp processing is normal moveout velocity analysis our objectives are to show the effect of multiple velocity analyses on the stacked radar image and particularly to demonstrate that this velocity information can also be used to determine subsurface water content most gpr surveys are very limited in spatial extent and assume that within the survey range radar velocity structure in the shallow subsurface can be adequately approximated by a single velocity function in data processing in this study we show that variation in radar velocity can be quite significant and that the stacked profile improves as the number of velocity analysis locations is increased interval velocities can be calculated from the normal moveout velocities derived in the cmp velocity analysis with some reasonable assumptions about subsurface conditions necessary for radar propagation interval velocity can be converted to an estimate of volumetric water content therefore by collecting gpr data in the multioffset cmp geometry not only is the radar profile improved but it also allows for an interpretation of subsurface variation in water content we show the application of these techniques to multioffset gpr data from the chalk river test area operated by atomic energy of canada limited