Aeromagnetic data are routinely acquired by mineral exploration programmes. The objective is to obtain a raster image of the spatial variations of magnetic field intensity; these variations are associated with mineralogical variations in the subsurface. When the survey is conducted in a populated area, much of the signal, however, may be associated with anthropogenic sources such as buildings and roads. Identification and minimization of the anthropogenic-related signal then are essential to derive a useful product for geological mapping. In this work, we examine a scalar magnetic dataset from Geyer, Saxony, and we apply five approaches for locating regions of anomalous anthropogenic signal: signal amplitude, absolute fourth difference, signal standard deviation, enhanced horizontal gradient and curvedness. All are shown to produce similar responses, and the summation of the five results compares favourably with the standard Keating kimberlite (circular anomaly) approach for detecting anthropogenic signals. Complications arise when geological features produce signals of similar amplitude to anthropogenic sources. Differentiating the probable origin of any specific pattern can be assessed by using a 2D shape index and increased flight height. Verification of an anthropogenic anomaly is achieved by comparison of anomalous solution grids with Geographic Information System-based reference data.

There is a clear demand to increase detection depths in the context of raw material exploration programs. Semi-airborne electromagnetic (semi-AEM) methods can address these demands by combining the advantages of powerful transmitters deployed on the ground with efficient helicopter-borne mapping of the magnetic field response in the air. The penetration depth can exceed those of classic airborne EM systems because low frequencies and large transmitter-receiver offsets can be realized in practice. A novel system has been developed that combines high-moment horizontal electric bipole transmitters on the ground with low-noise three-axis induction coil magnetometers, a three-axis fluxgate magnetometer, and a laser gyro inertial measurement unit integrated within a helicopter-towed airborne platform. The attitude data are used to correct the time series for motional noise and subsequently to rotate into an earth-fixed reference frame. In a second processing step, and as opposed to existing semi-AEM systems, we transform the data into the frequency domain and estimate the complex-valued transfer functions between the received magnetic field components and the synchronously recorded injection current by regression analysis. This approach is similar to the procedure used in controlled-source EM. For typical source bipole moments of 20–40 kAm and for rectangular current waveforms with a fundamental frequency of approximately 10 Hz, we can estimate reliable three-component (3C) transfer functions in the frequency range from 10 to 5000 Hz over a measurement area of [Formula: see text] for a single source installation. The system has the potential to be used for focused exploration of deep targets.

The Federal Institute for Geosciences and Natural Resources has recently launched a project to characterise soils and soil patterns using smart sets of newly developed and existing technologies on regional scales. The focus lies on the combination of airborne geophysical tools like gamma ray spectrometry and remote sensing techniques such as VIS-NIR-SWIR-LWIR hyperspectral and thermal infrared imagery. In order to calibrate the measurements all given methods will be implemented on ground and on soil samples in the laboratory. Additionally, geochemical, mineralogical and physical investigations well established in soil sciences will be incorporated. The aim is to map and evaluate the physical properties acquired from drones, helicopter and satellites. Using statistical methods and means of artificial intelligence areas of homogeneous physical soil properties will be determined. The resulting areas will be compared to soil classification maps and the distribution of soil substrates. Self organising map systems will be used for correlation of homogeneous areas and later interpretation. Major care will be taken to reduce effects from varying soil moisture and surface vegetation. The presentation will focus on ground based, airborne and space platforms and their instrumentation and current developments. Apart from off-road vehicles at least three different sets of drones will be used for detailed surveying, implementing newly developed gamma ray sensing systems, hyperspectral and thermal infrared cameras. The BGR helicopter will be equipped with a high-end gamma spectrometer and imaging hyperspectral sensors. We envisage using future hyperspectral EnMAP data to evaluate it against the helicopter results and further up- and downscaling strategies.

Seawater intrusion has often resulted in scarce fresh groundwater resources in coastal lowlands. Careful management is essential to avoid the overexploitation of these vulnerable fresh groundwater resources, requiring detailed information on their spatial occurrence. Airborne electromagnetics (EM) has proved a valuable tool for efficient mapping of ground conductivity, as a proxy for fresh groundwater resources. Stakeholders are, however, interested in groundwater salinity, necessitating a translation of ground conductivity to groundwater salinity. This paper presents a methodology to construct a high-resolution (50 x 50 x 0.5 m(3)) 3D voxel model of groundwater chloride concentration probability, based on a large-scale (1800 km(2), 9640 flight line kilometres) airborne EM survey in the province of Zeeland, the Netherlands. Groundwater chloride concentration was obtained by combining pedotransfer functions with detailed lithological information. The methodology includes a Monte Carlo based forward uncertainty propagation approach to quantify the inherent uncertainty in the different steps. Validation showed good correspondence both with available groundwater chloride analyses, and with ground-based hydrogeophysical measurements. Our results show the limited occurrence of fresh groundwater in Zeeland, as 75% of the area lacks fresh groundwater within 15 m below ground surface. Fresh groundwater is mainly limited to the dune area and sandy creek ridges. In addition, significant fresh groundwater resources were shown to exist below saline groundwater, where infiltration of seawater during marine transgressions was hindered by the presence of clayey aquitards. The considerable uncertainty in our results highlights the importance of applying uncertainty analysis in airborne EM surveys. Uncertainty in our results mainly originated from the inversion and the 3D interpolation, and was largest at transition zones between fresh and saline groundwater. Reporting groundwater salinity instead of ground conductivity facilitated the rapid uptake of our results by relevant stakeholders, thereby supporting the necessary management of fresh groundwater resources in the region.

Summary The DESMEX Project aims to develop semi-airborne systems for mineral exploration down to depths of about 1 km. The main system components have been tested and improved over last two years. After several preliminary test surveys, the main experiment was conducted in October 2017. Different layouts for the ground based survey set up were tested and evaluated. Large parts of the acquired data have been processed and first results are ready for display. Parallel to these works, petrographic studies have been performed in order to be able to complement the geophysical and geological data needed for a combined 3D-model of the main DESMEX survey region.

s Session 1 SESSIONS DESCRIPTION Session 1. Instrumentation, sources and data processing This session solicits contributions on EM data processing, source field analysis, instrumentation, and field practice. We welcome contributions on all aspects of data processing, including theory and practical applications. Development and application of time lapse observations (monitoring) of transfer functions and other parameters as well as new approaches to estimation of transfer functions and their uncertainty can be presented here. We also solicit studies on source fields, whether controlled or uncontrolled. This includes characterization of external source spatial structure and temporal variability, novel (distributed) transmitter configurations, and effects of finite spatial-scale sources (natural and anthropogenic) on transfer functions. Contributions on new instrumentation and field practice and related methodological developments are also appropriate for this session. Studies of sensor fidelity either by noise level analysis or by field comparison with other sensors are appropriate. Sensors can include ohmic or capacitively coupled electrodes, magnetometers, and any other instruments whose inter-comparison with EM data demonstrates new insights. Conveners: Pierre Wawrzyniak, Karl Kappler, Maxim Smirnov Abstract, 24th EM Induction Workshop, Helsingør, Denmark, August 12-19, 2018 24th EM Induction Workshop, Helsingør, Denmark, August 12-19, 2018 1 / 1 A Compact Ocean Bottom ElectroMagnetic Field Receiver& Seismometer Kai Chen1, Li Zhou2, Ming Deng3, Zhongliang Wu4and Xianhu Luo5 1 China University of Geosciences (Beijing), ck@cugb.edu.cn 2 China University of Geosciences (Beijing), zhouli100083@163.com 3 China University of Geosciences (Beijing), dengming@cugb.edu.cn 4 Guangzhou Marine Geological Survey, 52936891@qq.com 5 Guangzhou Marine Geological Survey, Luoxh@163.com

The German Federal Institute for Geosciences and Natural Resources (BGR) initiated a research project which combines remote sensing and geophysical data to improve the detection and 3D-characterisation of mineral resource deposits. To evaluate this new approach, hyperspectral remote sensing, airborne full tensor gradient magnetometry and gamma-ray spectrometry data will be acquired. Test areas are mining regions with Cu-Pb-Zn mineralisation of volcano-sedimentary-hosted massive sulphide deposits in Aznalcóllar — Los Frailes and Tharsis in the Iberian Pyrite Belt/Spain. This paper presents the concept of this project, preliminary results of field and laboratory reflectance spectroscopy of rock samples in the visible, near- and shortwave infrared as well as results of the airborne gamma-ray spectrometry and gradient magnetometry campaign.

(1) Federal Institute for Geosciences and Natural Resources (BGR), B2: Ground Water and Soil, Hannover, Germany, (2) Federal Institute for Geosciences and Natural Resources (BGR), B4: Geoscientific Information, International Cooperation, (3) Leibniz Institute for Photonic Technologies, Jena, Germany, (4) Supracon AG, Jena, Germany, (5) Federal Institute for Geosciences and Natural Resources (BGR), B1: Energy Resources, Mineral Resources, Hannover, Germany

Summary A novel semi-airborne frequency domain system is developed within the DESMEX project. The system is designed to achieve a penetration depth of about 1km with an areal coverage of about 6×6km2 per source installation on the ground. Here, we report on first results achieved with the new system. Horizontal electric dipole transmitters were used to inject time-varying electrical currents into the ground, and both a three-axis induction coil set up (Metronix MFS-11e) and a fluxgate (Bartington MAG-03) were installed on a helicopter-towed platform. We measure the induced magnetic field in the air in a frequency range from 1Hz to 10kHz. Additionally recorded attitude data can be used for correction of motion noise and for in-flight calibration to determine orthogonality and scaling errors in the fluxgate data as well as orientation errors of all sensors within the bird. In a first flight test the corrected fluxgate data shows a good signal-to-noise-ratio in the range 10ߝ400Hz with a noise level generally below 50pT/√Hz. The coils yield superior noise levels of less than 1pT/√Hz at frequencies higher than 400Hz. Frequency-domain response functions between the magnetic field and the source current are found to be consistent with subsurface conductivity structures.

Summary In the project FRESHEM Zeeland the entire Province of Zeeland in the south-western part of the Netherlands was surveyed using frequency-domain helicopter-borne electromagnetics (FDHEM). The airborne survey of more than 9000 line-km was conducted in 2014–15 by the German Federal Institute for Geosciences and Natural Resources (BGR). Together with the Dutch partners Deltares and TNO, an approach has been developed to translate the FDHEM data into a full 3D mapping of the chloride concentration of an area of about 1800 km2. Verification with an independent dataset showed that groundwater salinity can be accurately calculated based on FDHEM measurements and a stochastic lithological model. Using indicator kriging as interpolation method turns out to be suitable to construct a 3D voxel model, revealing high resolution spatial patterns of groundwater salinity.

One of the major tasks of the Federal Institute for Geosciences and Natural Resources (BGR – Bundesanstalt für Geowissenschaften und Rohstoffe) is to contribute to a sustainable future supply for Germany with minerals for industrial use. Part of the BGR’s strategy is to develop innovative ways of mineral exploration. The presented study focusses on airborne technologies, being applied and developed in ongoing projects. The methods used can be classified in established methods and newly evolving systems. The repertoire of established methods includes airborne electromagnetics, magnetics, radiometry and hyperspectral imaging. Systems based on latest technologies are full tensor magnetic gradient (FTMG) systems and audio-frequency magnetics (AFMAG) systems. Since a single airborne system usually cannot reveal the whole complexity of mineral bearing structures, new combinations of survey systems are being tested and new techniques are under development. The projects used to demonstrate and develop new systems, combinations and designs are E3 (Ore exploration in the Ore Mountains of Saxony, Germany), HYPGEO (New procedures for exploration of mineral raw materials using hyperspectral and geophysical sensing systems) and DESMEX (Deep Electromagnetic Sounding for Mineral Exploration). HYPGEO is being introduced as a new conceptual project combining different sensing systems and resources of BGR and partners.

Soil is one of the most precious resources on Earth. Preserving, using and enriching soils are most complex processes that fundamentally need a sound regional data base. Many countries lack this sort of extensive data or the existing data must be urgently updated when land use recently changed in major patterns. The project "RECHARBO" (Regional Characterization of Soil Properties) aims at the combination of methods from remote sensing, geophysics and geopedology in order to develop a new system to map soils on a regional scale in a quick and efficient manner. First tests will be performed on existing soil monitoring districts, using newly available sensing systems as well as established techniques.

Summary Airborne geophysical methods have a great potential in delineating subsurface information down to some hundred metres depth. This information is essential for planning purposes for manifold geoscientific, economic or environmental questions, like, e.g., utilization and protection of freshwater resources, land utilization or industrial planning. These data integrated into a three-dimensional geographic information system provide a powerful tool for spatial planning. Beside the geological or geophysical basic information also changes of surface and subsurface data in time and space may be documented by repeated surveys. In this contribution, typical applications of helicopter-borne electromagnetics in Germany are shown. The surveys were conducted by BGR using a six-frequency RESOLVE system. Emphasis is placed on the mapping of coastal aquifers, what comprises the mapping of freshwater-saltwater interfaces, the outline of saltwater intrusions and submarine freshwater occurrences, and the mapping of clay distributions.

Airborne geophysical methods have a great potential to explore the surface and subsurface of the earth down to some hundred meters depth. This information is essential for planning purposes for manifold geoscientific, economic or environmental questions, like, e.g., utilization and protection of freshwater resources, land utilization or industrial planning. These data integrated into a three-dimensional geographic information system provide a perfect tool for spatial planning. Beside the geologic or geophysical basic information also changes of surface and subsurface data in time and space may be documented by repeated surveys. The Federal Institute for Geosciences and Natural Resources (BGR) operates a helicopter which can be equipped with the following BGR-own and external geophysical systems (Figure 1): frequency-domain electromagnetics, magnetics, gamma-ray spectroscopy, gravimetry, stepped-frequency and pulse radar. In addition, the helicopter can be used for airborne remote sensing (Laser scanning (LIDAR), aerial photography and infrared thermal imaging). Overall, the BGR helicopter with its performance and features is at least in Western Europe a unique measurement and research platform that can be used to investigate a variety of geo-scientific issues.

Coastal areas such as the German Bight are at risk from storms and rising sea level that may affect the hydrogeologic setting. Because knowledge of the distribution of clayey sediments is important for understanding the current status of this dynamic setting, the German Federal Institute for Geosciences and Natural Resources (BGR) has focused on geophysical research projects on the North Sea coast applying airborne and ground geophysics. The airborne system operated by BGR was used to survey a 20- by 31-km large coastal area in Eastern Friesland, Germany, including the islands of Langeoog and Spiekeroog. Helicopter-borne electromagnetic (HEM) data were collected at six frequencies. In addition, the Leibniz Institute for Applied Geophysics commissioned a SkyTEM survey covering a 2-km-wide north–south strip. On the island of Langeoog, ground geophysical methods, such as transient electromagnetics (TEM) and magnetic resonance soundings (MRS) were used to investigate the hydrogeologic setting in greater detail. Onshore, the airborne electromagnetic results clearly outlined a complex electrically conductive pattern occurring at a shallow depth. Comparison with borehole results provided by the State Authority for Mining, Energy and Geology confirmed that these conductors were caused by clayey material, particularly down to an approximate 20-m depth. This pattern continues offshore, and it is likely that the saltwater is linked to stripes of clayey sediments and the fresh groundwater flows out to the Wadden Sea in between. On the islands, the HEM results revealed the freshwater lenses and showed some indications for clay layers within these freshwater lenses. The application of TEM and MRS helped to distinguish lithology from salinity and confirmed the existence of these clay layers. We demonstrated the usefulness of combining the spatial airborne data with geophysical and borehole data available at sparsely distributed sites on the ground to investigate hydrogeologic settings.

The aim of this work is to deploy a new SQUID (Superconducting Quantum interference device) based instrument for the measurement of the full magnetic gradient tensor of the Earth’s magnetic field in survey scenarios in a sedimentary basin in Thuringia, a local province in Germany. This task requires developing according processing, inversion, and interpretation techniques for this new instrument. The recent state of the instrument and data processing techniques is presented. The new instrument has several advantages compared to commercially available high-resolution aeromagnetic survey instruments. Besides the fact that weaker magnetic anomalies could be detected, it delivers vector data and thus more detailed information even on remanence of the geologic structures. It is required for more enhanced magnetic anomaly delineation and possibly for the determination of the age of intrusive or alteration structures. As a proof of principle a small-scaled magnetic anomaly on the border of the Thuringian basin was selected. The area was mapped in 2013. The results are presented and preliminary results of the inversion discussed which indicate remanent magnetization of the rocks which cause the magnetic anomaly.

In this chapter we report on the deep structure of the Dead Sea Transform (DST) as derived from geophysical observations and numerical modelling, calibrated by geological and geodynamic evidence. We use seismics, seismology and gravity to study the crust and lithosphere of the Dead Sea Transform (DST) system. These observations are integrated with 3D thermo-mechanical modelling of the evolution of the DST through time to understand the deeper structure of the DST. The three seismic profiles crossing the DST from the Mediterranean in the West to the Jordan highlands in the East show an increase in Moho depth from about 25 km to about 35 km; with only minor topography. This depth increase of about 10 km of the Moho from West to East is also found in tomographic images using regional and teleseismic events, which shows additionally a N - S trending thickening of the crust under the Arava/Araba Fault (AF). In the Dead Sea Basin (DSB) proper the imaging of the Moho is complicated by the presence of the Lisan Salt dome. From these results and other evidence we conclude that the Dead Sea basin is a mostly upper crustal feature with a decoupling zone at about 20 km depth. Using SKS waves we find below the Moho under the DST a narrow, ca. 20 km wide, vertical decoupling zone reaching into the mantle, representing the boundary layer between the African and Arabian plates. This observation agrees with the results from the study of surface waves that also show a region of reduced S-velocities under the DST, reaching down into the lithosphere. Whereas the lithosphere thins gradually east of the DST from N to S from ca. 80 to ca. 67 km, below about 120 km depth little structure can be observed in tomographic images. The abovementioned observational constraints can all be fitted with the classical pull-apart model, if the lithosphere was thermally eroded to 80 km thickness about 20 Ma ago, combined with weak rheologies for crust and upper mantle. The most likely explanation of the features described is thus a thinning of the lithosphere around the DST in the Late Cenozoic, likely following by rifting and spreading of the Red Sea.