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The duration of time domain (TD) induced polarization (IP) current injections has significant impact on the acquired IP data as well as on the inversion models, if the standard evaluation procedure is followed. However, it is still possible to retrieve similar inversion models if the waveform of the injected current and the IP response waveform are included in the inversion. The on-time also generally affects the signal-to-noise ratio (SNR) where an increased on-time gives higher SNR for the IP data.

The applicability of the magnetic resonance sounding (MRS) technique in urbanized areas is limited by the inherently weak signal from the subsurface water which is often deeply buried in noise from anthropogenic sources. The noise can have spatially variations on even sub-100 m scales and the signal to noise ratio of an MRS measurement can therefore be optimized by a careful choice of the exact location. In this paper we present an instrument for fast mapping and analysis of the noise conditions at a site prior to MRS experiments. The main components of the instrument are two induction receiver coils connected to amplifiers and a digital oscilloscope controlled by a PC. Analysis of the gathered data reveals the spatial distribution of the different noise components, in particular powerline harmonics and spikes. A comprehensive noise map of a test site is presented and analyzed.

En flad (dybde Thesegeological enheder er særdeles vigtigt, både miljømæssigt og økonomisk. Airborneelectromagnetic (AEM) er der benyttet tal med nogen succes at opnå havdybder ofshallow overfladevand ((Macnae et al., 2004; Vrbancich et al., 2000; Vrbancich et al., 2005). Nogle forsøg er også blevet gjort for at hente oplysninger om sub-bunden (Vrbancich et al., 2000). begrænsede forskning, der udføres så vidt opfordrer til forbedringer andfurther udvikling, både hardware og databehandling og modellering. Denne manuscriptaims at give et bidrag på data inversion niveau, ved at anvende Den begrænsede inversionmethodology til forskellige AEM datasæt fløjet over vand. I denne teknik, tilstødende modelparameters er afklaret gennem lateral begrænsninger, som tillader, at oplysninger strøm fromsoundings, der indeholder mere til dem, der indeholder mindre. Vi præsenterer resultater fra constrainedinversion (glat og få lag) af en del af SkyTEM (TEM system) undersøgelse fløjet inDenmark, og af en LOESE (HEM-systemet) undersøgelse foretaget langs Murray floden inAustralia. I begge tilfælde fugl højde blev inkluderet som en omvending parameter, allowingcompensating for fejl i laser højdemåler læsning over vand. A shallow (depth < 20 m) layer of water, fresh, brackish or saline, covers of millions of km2of sediments and bedrock along the world's coastlines, rivers, lakes, and lagoons. Thesegeological units are extremely important, both environmentally and economically. Airborneelectromagnetic (AEM) data has been used with some success to obtain the bathymetry ofshallow surface water ((Macnae et al., 2004; Vrbancich et al., 2000; Vrbancich et al., 2005).Some attempts have also been made to retrieve information about the sub-bottom(Vrbancich et al., 2000 ). The limited research carried out so far calls for improvements andfurther developments, both hardware and in data processing and modelling. This manuscriptaims at giving a contribution at data inversion level, by applying the constrained inversionmethodology to different AEM datasets flown over water. In this technique, adjacent modelparameters are regularized through lateral constraints that allow information to flow fromsoundings that contain more to those that contain less. We present results from constrainedinversion (smooth and few layers) of a portion of SkyTEM (TEM system) survey flown inDenmark, and of a RESOLVE (HEM system) survey carried out along the Murray river inAustralia. In both cases bird height was included as an inversion parameter, allowingcompensating for errors in laser altimeter reading over water.

Summary Inversion of geophysical data is often challenging and time-consuming, particularly for large scale surveys. The solution of the inverse problem requires numerous calculations of the forward problem, especially when calculating partial derivatives required for most linearized inversion schemes. The forward model is usually calculated numerically using accurate equations, but often less accurate and faster equations are used. In recent years, neural networks have become increasingly popular to replace the numerical forward modelling, as this may lead to a significant speed-up. Data normalization, prior to the training of neural networks, is crucial to obtain good results and faster convergence rate. This is especially true for geophysical data, as numerical data values may span over several orders of magnitude. In this abstract, we investigate several normalization approaches for TEM data, with a special focus on towed TEM data. Through extensive experimentations, we show that data normalization substantially affects the performance of neural networks when surrogating forward models. We also demonstrate the effect of normalized data variation on neural network’s performance and provide insights into which normalization approaches may be better than others. A significant improvement in performance accuracy is achieved when the appropriate data normalization technique is employed.

Mutually constrained inversion in combination with laterally constrained inversion (MCI‐LCI) between transient electromagnetic (TEM) and direct current (DC) resistivity methods was successfully used to characterize a buried valley structure. Although both methods measure, in some sense, the electrical resistivity, or conductivity, of the subsurface, they sample different volumes and have different sensitivities, which are exploited with mutually and laterally constrained inversion of combined, coincident profile data sets. The output models incorporate the information from both data sets to obtain optimum layered 1D models, fitting both data sets and constraints. The set‐up of constraints contains three parts. First, we constrain the individual data sets along their profile using lateral constraints producing a chain of TEM data and a chain of DC data. Next, we merge the information from these two chains by setting up mutual constraints between the TEM and the DC models. Finally, we adjust the mutual constraints to resemble the increasing sampling volumes with depth, i.e. wide constraints at large depths and short constraints at shallow depths. All data sets are inverted simultaneously; a common objective function is minimized, and the number of output models is equal to the number of 1D soundings. The lateral and mutual constraints are part of the inversion, and consequently the output models are balanced between the constraints and the data‐model fit. Information from one model will spread to the neighbouring models through the constraints, helping to resolve parameters that are poorly resolved by any of the individual data sets. A field example illustrates that MCI‐LCI allows the governing information from each method to dominate the inversion process. Thus, the model resolution in both the shallow and the deeper parts of the model is significantly enhanced. This could not be obtained by inverting the two data sets separately with a subsequent comparison of the output models. Our results are confirmed by drill‐hole data.

The extraction of spectral information in the inversion process of time-domain (TD) induced polarization (IP) data is changing the use of the TDIP method. Data interpretation is evolving from a qualitative description of the subsurface, able only to discriminate the presence of contrasts in chargeability parameters, towards a quantitative analysis of the investigated media, which allows for detailed soil- and rock-type characterization. In this work a review of the recent advances in spectral inversion of TDIP data is presented, in terms of: supported IP parameterizations; modelling of transmitter waveform; support for buried electrodes; model regularization; computation of the depth of investigation.

The Magnetic Resonance Sounding (MRS) method, also known as surface NMR, is a non-invasive geophysical method which directly studies groundwater reservoirs from surface measurements. It is capable of direct estimating of water content distribution (from initial amplitudes) and indirect information on pore sizes (from relaxation time). The purpose of this paper is to introduce a new inversion scheme for the full MRS data set. The multiexponential behaviour of the NMR signal is taken into account and estimated by the Stretched-Exponential model (Hilfer, 2002), in which the time constant and stretching exponent determine the centre and the width of the distribution. The model space is then described with much less parameters, compared with the multi-exponential description. The FID time series are logarithmically gated and the discretization in the z-direction in the forward algorithm is decoupled from discretization of the inversion model. The inversion routine supports smooth and block inversion of the data and a full linear model parameter sensitivity analysis can be calculated (Tarantola and Valette, 1982), an essential criteria for evaluation of the inversion results.

Large-scale integrated hydrological models are important decision support tools in water resources management. The largest source of uncertainty in such models is the hydrostratigraphic model. Geometry and configuration of hydrogeological units are often poorly determined from hydrogeological data alone. Due to sparse sampling in space, lithological borehole logs may overlook structures that are important for groundwater flow at larger scales. Good spatial coverage along with high spatial resolution makes airborne time-domain electromagnetic (AEM) data valuable for the structural input to large-scale groundwater models. We present a novel method to automatically integrate large AEM data-sets and lithological information into large-scale hydrological models. Clay-fraction maps are produced by translating geophysical resistivity into clay-fraction values using lithological borehole information. Voxel models of electrical resistivity and clay fraction are classified into hydrostratigraphic zones using k-means clustering. Hydraulic conductivity values of the zones are estimated by hydrological calibration using hydraulic head and stream discharge observations. The method is applied to a Danish case study. Benchmarking hydrological performance by comparison of simulated hydrological state variables, the cluster model performed competitively. Calibrations of 11 hydrostratigraphic cluster models with 1–11 hydraulic conductivity zones showed improved hydrological performance with increasing number of clusters. Beyond the 5-cluster model hydrological performance did not improve. Due to reproducibility and possibility of method standardization and automation, we believe that hydrostratigraphic model generation with the proposed method has important prospects for groundwater models used in water resources management.

For continuous methods there is a trade-off between lateral resolution and the size of the data stack, or average width. A narrow average (small stack) results in a high lateral resolution, a wide average (large stack) results in a better signal-to-noise ratio but reduces the lateral resolution. We present inversion results of synthetic TEM-data with different averaging widths to explore the influence on the lateral resolution. The study shows that for the deeper parts of the model it is possible to use a very large average width without loosing lateral resolution. Averaging airborne data adds another issue, because the data entering the average interval originates from different flight altitudes (aircraft movement). The question is whether the error introduced by assigning the average flight altitude to the average dataset is acceptable? This is relevant because the altitude enters the inversion scheme as a fixed or strongly constrained parameter. We show that a linear correlation between altitude and data response for TEM-data exist. Due to the linearity the error introduced by using average data with the average altitude is very small. In the worst case, the error is 3% and negligible for the late time gates.

Resistivity and time domain IP measurements using a 100% duty cycle square waveform current injection signal, and measuring the IP responses during current transmission, was modelled numerically and tested in the field against a traditional IP current injection with a 50% duty cycle waveform and measuring during the current off-time. The results show that the approach is practically applicable and can reduce the measuring time substantially as well as increase the signal-to-noise ratio by measuring the IP-response during the current on-time.

This study uses time domain IP for the delineation and the characterization of the former Eskelund landfill, Denmark. With optimized acquisition parameters combined with a new inversion algorithm it is now possible to use the full content of the decay curve and retrieve spectral information from the time domain IP data. Thirteen IP/DC profiles were collected, supplemented by en el-log drilling for an accurate correlation between the geophysics and the lithology. The data were inverted using a laterally constrained 1D inversion considering the full decay curves to retrieve the four Cole-Cole parameters. For all profiles, the results reveal a highly chargeable unit with an impressive agreement to 15 boreholes. The thickness and the depths have been validated by el-log measurements giving in-situ values for the Cole-Cole parameters. The 3-D shape of the waste body has been delineated with a very high accuracy, and the south boundary of the landfill has been redefined based on these results. The inversion of the IP data also allows reconstruction of the waste history combining aerial maps with the results. Thus, this case study shows the relevance and the full benefits of using the TDIP data for the recognition and the characterization of landfill areas.

We have developed a new, robust 2D inversion approach for modelling time domain induced potential data. Instead of considering the integral chargeability, the full IP waveform is modelled allowing inversion for spectral content in terms of the Cole-Cole parameters. The method is based on a finite element complex resistivity forward response, which is transformed to the time domain using a Fast Hankel Transform. The forward response is implemented in a general inversion code where constraints can be applied on all model parameters to allow migration of information along the profile. A priori information from e.g. boreholes may also be included to constrain the inversion.

We present a new inversion methodology for large area-covering datasets. Many new data acquisition systems are capable of covering large areas with densely sampled data sets. However, it is not possible to apply 2D or 3D inversion algorithms on a routine basis because of computational problems. We propose a Spatially Constrained Inversion (SCI) inversion scheme using a local 1D model description ensuring fast computation times. Information on the geological variability is included as constraints between model parameters applied on an all-to-all basis. The 1D formulation means that the SCI works best on a sub-horizontal layered geology. To ensure flexibility even for very large surveys we sub-divide the area in hexagons, which are independently inverted and afterwards stitched together. Continuity over hexagon edges is ensured by applying an overlap between neighbouring hexagons. A field example demonstrates that the SCI enables better resolution of otherwise poorly resolved model parameters. Lineations observed in line-inversion are removed.

Between November 2009 and July 2010, researchers from the HydroGeophysics Group, Aarhus University, carried out a survey in the former municipallandfill, Eskelund (Denmark). Induced polarization measurements (IP) and electrical resistivity tomography (ERT) were used to define the spatial boundaries of thedump site. The joint application of these two methods may allow the discrimination between materials displaying an identical signature in resistivity (e.g., brine and clay)

Summary Surface NMR holds great promise as a tool in groundwater measurements due to its unique direct sensitivity to water, but the method currently suffers from a number of drawbacks which limits its widespread applicability. Among these drawbacks are a low signal to noise ratio which limits the use of the method in many places of interest and a low production rate which makes the method costly in field campaigns. Hence there is a need for research further advancing the technology. In this paper we report on the development of a new multichannel, low noise surface NMR receiver system with wireless connections to reference coils. The receiver system works as a completely independent add-on to existing transmitter systems and consists of a number of independently operated data acquisition boxes connected with WiFi and synchronized by GPS. The internal electronic noise level of the system is 1.2 nV/sqrt(Hz). The timing jitter between data acquired in different boxes is less than 100 ns.

We present an automatic method for parameterization of a 3D model of the subsurface, integrating lithological information from boreholes with resistivity models through an inverse optimization, with the objective of further detailing for geological models or as direct input to groundwater models. The parameter of interest is the clay fraction, expressed as the relative length of clay-units in a depth interval. The clay fraction is obtained from lithological logs and the clay fraction from the resistivity is obtained by establishing a simple petrophysical relationship, a translator function, between resistivity and the clay fraction. Through inversion we use the lithological data and the resistivity data to determine the optimum spatially distributed translator function. Applying the translator function we get a 3D clay fraction model, which holds information from the resistivity dataset and the borehole dataset in one variable. We apply the concept to the Norsminde survey in Denmark integrating approximately 700 boreholes and more than 100,000 resistivity models from an airborne survey in the parameterization of the 3D model covering 156 km2. The final 3D model differentiates between clay materials and different high resistive materials from information held in resistivity model and borehole observations respectively

We present a new scheme for joint and laterally constrained inversion (LCI) of magnetic resonance sounding (MRS) data and transient electromagnetic (TEM) data, which greatly improves the estimation of the MRS model parameters. MRS is a non-invasive geophysical technique which directly quantifies the water content distribution from surface measurements. The resistivity information of the subsurface is obtained from a complementary geophysical method such as TEM or DC resistivity methods. The conventional inversion of MRS data assumes the resulting resistivity structure to be true and considers a constant MRS kernel through the inversion. We show that this assumption may introduce an error to the forward modeling and consequently result in erroneous parameter estimations. We discuss the advantage of TEM for the joint inversion compared to DC resistivity. A fast and numerically efficient MRS forward routine makes it possible to invert the MRS and TEM data sets simultaneously along profiles. As results, a more reliable and robust estimation of all parameters is achieved. We examine the approach through a field example in Denmark where good agreement with borehole data is demonstrated with clear correlation between the relaxation time T_2^* and the grain size distribution of a sandy aquifer.

In a sedimentary environment, quasi‐layered models often can represent the actual geology more accurately than smooth minimum‐structure models. We present a 2D inversion scheme with lateral constraints and sharp boundaries (LCI) for continuous resistivity data. All data and models are inverted as one system, producing layered solutions with laterally smooth transitions. The models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers. A priori information, used to resolve ambiguities and to add, for example, geological information, can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites. Similarly, information from areas with well‐resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters. The estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result.A simple synthetic model proves the need for a quasi‐layered, 2D inversion when compared with a traditional 2D minimum‐structure inversion. A 2D minimum‐structure inversion produces models with spatially smooth resistivity transitions, making identification of layer boundaries difficult.A continuous vertical electrical sounding field example from Sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example. A till layer on top of the bedrock, hidden in the traditional inversion result, is identified using the 2D LCI scheme. Furthermore, the depth to the bedrock surface is easily identified for most of the profile with the 2D LCI model, which is not the case with the model from the traditional minimum‐structure inversion.

The spatially constrained inversion (SCI) is a robust methodology for quasi-3D modeling of geoelectrical and EM data of varying spatial density, using a 1D forward solution. Information migrate horizontally through spatial constraints applied between nearest neighboring soundings, and allow resolution of layers that would be locally poorly resolved. The constraints are built using the Delaunay triangulation, which ensures automatic adaptation to data density variations. In this study the SCI was applied to airborne Time domain EM soundings, but it can be implemented also with other data types. The field case study proves that the SCI produces laterally smooth results that respect the 3D geological variations of sedimentary settings, while suppressing the elongated artifacts commonly seen in profile oriented data sets.

Magnetic resonance sounding (MRS) is a unique and promising hydrogeophysical technique. Due to its ability of providing a direct estimate of the water content and estimates of the porosity in the subsurface, MRS has the potential of being a great team player in the field of hydrological prospecting. However, the MRS measurements suffer from a low signal to noise ratio due to the signal being inherently weak and the susceptibility to electromagnetic interference. The low signal to noise ratio currently impedes the applicability of the technique, particularly in urban areas. In recent years the development of multichannel MRS has opened up new possibilities for advanced noise cancellation methods. Before multichannel MRS can realize its full potential robust and reliable methods for noise cancellation must be developed. In this work we compare two noise cancellation methods: The multichannel Wiener filter and a multichannel adaptive noise cancellation filter. The comparison is performed on noise records from a multichannel MRS instrument with or without synthetic signal added. Our results show that adaptive noise cancellation performs better than the Wiener filter for both pure noise removal and for recovery of the parameters of the synthetic signal.

Today, negative induced polarization (IP) time-domain responses and responses with non-standard shapes are generally considered as measurement errors and removed in data processing before inversion. However, synthetic and field measurements show that these responses are in fact physically possible and that a simple theoretical explanation of the basic mechanism for their origin can be found by means of superposition of contributions from regions with different sensitivities. The basic mechanism for IP responses with non-standard shapes is investigated by considering the subsurface Cole-Cole parameter sensitivities and time varying IP potential for 2D synthetic models. The time-domain forward response and sensitivities are computed from the finite-element solutions of the frequency-domain differential equation, through a time transformation that takes the current waveform into account. This approach allows for quantitative unbiased estimates of the time-domain responses and sensitivities, which are different from the estimates that can be obtained when using multiple DC forward computations, as often done in the inversion of time-domain IP data. With the increased understanding, previously disregarded IP responses, which can contain valuable information of the subsurface, can be kept for the inversion process and thus contribute to the final parameter distribution.

Time-domain induced polarization (IP) and magnetic data were acquired to map and characterize the decommissioned, un-engineered, municipal solid waste deposit site of the Kwame Nkrumah University of Science and Technology (KNUST), located in the Kumasi Metropolis of Ghana. Thirteen induced polarization profiles 500-800 m long and twenty-six magnetic profiles 600-800 m long were acquired, and two drillings were carried out in order to help in the interpretation of the geophysical data. The study was carried out with the aim of determining the risk posed by the waste deposit to the quality of the soil and the groundwater system, which is the main potable water supply for the Secondary School, the University Teaching Hospital and the Veterinary School, situated within the catchment area of the site. Full-decay 2-D time-domain IP inversions in terms of Cole-Cole parameters were used for interpreting the polarization data. The chargeability, resistivity, and the normalized chargeability distributions, together with the magnetic results, aided in a full characterization of the site geology, the waste and the associated pollution plume. In particular, clear contrasts in resistivity and in the polarization parameters were found between the saprolite layer and the granite bedrock, the main lithological units of the area.Furthermore, it was found that the KNUST waste deposit is characterized by a low-chargeability and low-resistivity signature, and that the low-resistivity area spreads out from the waste deposit into the permeable saprolite layer,indicating the presence of a leachate plume. A fracture zone in the granite bedrock, which is at a risk of leachate contamination, was also identified. The research thus provides the information needed for assessing the future impact of the waste on the water quality in the area as well as for designing risk-mitigation actions.

Leaching of organic and inorganic contamination from landfills are a serious environmental problem as surface waters and aquifers are being contaminated. In order to assess these risks and investigate the migration of leachate from the landfill, several time-domain DCIP profiles have been collected at a heavily polluted landfill in Grindsted, Denmark. The DCIP data were inverted using a new 2D DCIP inversion code inverting for a full cole-cole model while modelling the full system transfer response including waveforms, gates and low-pass filters. The inverted profiles describe both the variations along the groundwater flow as well as the plume extension across the flow directions. Chemical analysis of borehole data agrees well with the observations indicating a leachate plume which gradually sinks and increases in size while migrating from the landfill in the groundwater flow direction. High chargeabilities are seen on the landfill itself but there are only small IP effects in the leachate migrating from the landfill. The information obtained from the DCIP results will be combined with chemical analysis in order to compute contaminant mass discharge. Hence, the DCIP data provides invaluable spatial information on the leachate characteristics, which cannot be obtained from boreholes alone.

Recent improvements of the transient electromagnetic (TEM) method provide unprecedented capabilities of imaging geological features in the uppermost few hundred metres of the subsurface. This is documented with an example from the island of Mors, Northern Jutland, Denmark, where 2655 TEM soundings have been acquired as a part of Viborg County’s hydrogeological investigation programme. Horizontal aspects of the interpreted TEM soundings are presented in thematic maps revealing variations of resistivities in specified depth intervals and depths to the resistivity basement, i.e. the deepest recorded low-resistive layer. Vertical aspects are displayed in cross-sections.The dense coverage of TEM soundings, combined with borehole logs, allows the precise delineation of major geological features. These comprise the Mors salt diapir, intricate systems of buried Quaternary valleys and several glaciotectonic complexes, all contributing to a complicated geological framework for the island. The layers above the salt diapir, which have been subject to severe erosion, are distinctly imaged in the thematic maps, even though they are frequently dissected by buried valleys. At least four generations of buried valleys can be identified on the basis of their preferred orientations; these were mainly formed during early glaciations. Large parts of the island were glaciotectonically deformed during the Late Weichselian subsequent to valley formation, and it is suggested that the presence of deep valleys may have affected the process of glaciotectonic deformation.

Contamination of potable groundwater by leaking CO2 is a potential risk of carbon sequestration. With the help of a field experiment, we investigate if surface electrical resistivity tomography (ERT) can detect dissolved CO2 in a shallow aquifer. For this purpose, we injected CO2 at a depth of 5 and 10 m and monitored its migration using 320 surface electrodes on a 126 m × 20 m grid. A fully automated acquisition system continuously collected data and uploaded it into an online database. The large amount of data allows for time-series analysis for data quality and noise estimation. A baseline inversion reveals the geology at the site consisting of aeolian sands near the surface and glacial sands below 5 m depth. Time-lapse inversions clearly image the dissolved CO2 plume with decreased electrical resistivity values. We can follow the CO2 plume as it spreads and moves with the groundwater, and the spatial distribution of the plume agrees well with direct measurements of the groundwater resistivity. Future work will include improved time-series analyses and quantitative comparison with the groundwater resistivity measurements.

Geofysisk udstyr, der benytter elektromagnetisk induktion (EMI), har været anvendt til kortlægning af geologiske strukturer i mange år. I de seneste få år er udstyr til 3D-kortlægning af de øverste 3-8 meter af jorden dog væsentlig forbedret, og egentlige kvantitative tolkninger af data med præcis identifikation af fx laggrænser og lagfølger er muligt. Metodikkerne, der anvendes, er i høj grad afledt af mange års arbejde med data fra bl.a. grundvandskortlægningen. Geofysikudstyret trækkes af en ATV og koblet med GPS-data kan store arealer kortlægges omkostningseffektivt. I indlægget her vises to eksempler: 1) fra EMI kortlægning af sø- og oddeudviklinger ved jernalderofferfundet i Alken enge(Mossø), hvor paleolandskabet har stor betydning for nutidige bevaringsforhold for af det arkæologisk materiale, og 2) landskabsformer samt voldopbygninger ved vikingetidsborgen Borgring ved Køge. Yderligere introduceres potentialet for arkæologisk kortlægning med et nyt state-of-the-art fluxgate gradient-magneometer udstyr, som Aarhus Universitet netop har opbygget.

Key to the effective management of natural ecosystems that characterise the floodplains of the Murray Basin in south eastern Australia, and maintenance of river health (a critical water resource) in a setting where severe salinisation is an ever-present threat, requires a sound understanding of surface water-groundwater processes. This paper presents results from an examination of hydrogeophysics, specifically airborne electromagnetics (AEM) data acquired by the SkyTEM time domain helicopter EM system, as a means for improving our knowledge of spatial patterns associated with inter-aquifer mixing where groundwater flow is complex. In the south-eastern part of the Murray Basin, AEM data shows considerable promise as a means for understanding of groundwater quality and its lateral variability. In the Bookpurnong and Loxton irrigation areas the high moment capability of SkyTEM permits us to investigate variations in the quality of groundwater at depth (>100m), which in turn allows us to visualise how groundwater may be moving across aquitards and within particular aquifer systems.

Development of more time-efficient and airborne geophysical data acquisition systems during the past decades have made large-scale mapping attractive and affordable in the planning and administration of e.g., groundwater resources or raw material deposits. The handling and optimized use of large geophysical data sets covering large geographic areas requires a system that allows data to be easily stored, extracted, interpreted, combined and used one time after another with different purposes. Such an integrated system for management and utilization of hydrogeophysical data on a national scale has been developed during the past decade in Denmark. This data handling system includes a comprehensive national geophysical data base (the GERDA data base), a national data base for borehole information (the Jupiter data base), a program package for processing, interpretation and visualization of electrical and electromagnetic data as well as preparation of these data for upload to the geophysical data base (the Aarhus Workbench) and finally a 3D visualization and modelling tool used for geological modelling and data quality control. The Aarhus Workbench program package allows visualization and analysis of subsets of data from the geophysical data base, which may include data from many individual mapping campaigns. The 3D visualization and modelling tool uses data from the geophysical and the borehole data bases directly; moreover, it handles maps and grids produced in the Aarhus Workbench. The integrated system for management of hydrogeophysical data allows management of large amounts of data collected over several years in different mapping campaigns, of different consultant companies and with different geophysical methods and instrumentation. It is now used by all partners involved in the groundwater mapping in Denmark. The system promotes reuse of geophysical data and models in future mapping projects, as well as easing and promoting the use of geophysical data in the geological modelling. The integrated system secures transfer of documentation all the way from data acquisition over processing and inversion of the geophysical data to geological modelling through storage of data acquisition parameters, data processing parameters, inversion parameters and uncertainties on data and models in the geophysical data base. The benefits of the large amount of geophysical data gathered in the national geophysical data base and utilized by the two program packages are invaluable for all future groundwater planning and administration.