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Near Surface 2006 - 12th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 04 Sep 2006 - 06 Sep 2006
- Location: Helsinki, Finland
- ISBN: 978-90-73781-62-7
- Published: 04 September 2006
1 - 20 of 142 results
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Why Not X in Airborne TEM?
Authors E. Auken, A. V. Christiansen and K. SørensenWe describe the challenges for the realization of a transient EM (TEM) system capable of measuring both the z- and x-components. This involves significant changes to instrumentation as well as to the processing and inversion algorithms.
Geophysical mapping of groundwater resources using TEM involves both delineation of the aquifer structure and the aquifer protection. The demands for the instrumentation and the processing algorithms are quite different for the two tasks. Structural mapping requires large depth penetration and thereby a large transmitter moment while aquifer protection mapping requires early time measurements and extremely accurate determination of the system transfer function. Furthermore, the inversion software must be capable of modelling this system transfer function.
For an airborne TEM system systematic analysis of the resolution capabilities of relatively thin low resistive layers in the upper 30 - 50 m of the subsurface has shown that the resolution is enhanced if not only the transient z-component but also the transient x-component of the induced fields in the Earth is measured and included in the inversion.
The abstract will describe and discuss three major challenges related to the inclusion of the x-component in an airborne TEM system.
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The New 4-Frequency Airborne EM System of JAC
Authors M. Kurimo, I. Suppala, H. Leväniemi and M. LahtiGeological Survey of Finland (GTK) and British Geological Survey (BGS) have jointly (JAC) constructed a new, 4-frequency EM unit installed in a fixed-wing aircraft. The system follows the technique of the previous dual frequency unit of GTK. The frequence range is now from 0,9 to 25 kHz. The four separate coils are installed inside the pods situated at the wing-tips, the separation between transmitter and receiver coils being 21.4 m. The system sensitivity is wide, covering well geological and environmental targets, and the lowest frequency enhances the depth penetration.
This paper describes the technical characteristics of the new system: specifications and noise level, and analyses the half space model responses. A test area survey was performed to find out the possibilities to utilise the data in interpretation. A 3D model based on systematic 1D inversion was compiled successfully.
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Laterally Constrained Inversion of Fixed-Wing Frequency-Domain AEM Data
Authors E. Tartaras and D. BeamishNew high-resolution airborne geophysical surveys of the UK, undertaken with the system developed under the Joint Airborne-geoscience Capability programme, established between the Geological Survey of Finland and the British Geological Survey, will provide large 4-frequency airborne electromagnetic data sets. These data sets will be used to characterise the conductivity distribution of the subsurface for environmental and exploration purposes. To invert these large data sets in a fast and robust manner we have developed “LC1DINV”, a laterally constrained one-dimensional inversion algorithm. This algorithm inverts simultaneously for all observation points along a profile and regularises the inverse problem by requiring that differences between model parameters at adjacent points be small. We use the conjugate gradient method for minimising the data misfit subject to the lateral constraints and a priori model terms. We have inverted 4-frequency data obtained over Suurpelto, a test area in southern Finland, characterised by conductive clays overlying a highly resistive granitic shield. The results show that LC1DINV can successfully locate the depth extent and variations of the clays. Comparison of these results with those obtained with two other types of inversion shows that LC1DINV produces well-defined layer boundaries and laterally smooth cross-sections.
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Laterally Constrained 1D Inversion of Airborne Electromagnetic Data
Authors M. T. Pirttijärvi and J. LerssiThe transformation of airborne electromagnetic (AEM) data into apparent resisitivity and depth is traditionally made separately for each measurement point and does not take into account the neighbouring data or model values or multiple frequencies. Laterally constrained inversion, where the model roughness is minimized together with the data error using a 1-D layered earth model, provides an easy and fast method to transform multi-frequency AEM data into a physically more meaningful form. The method is based on linearised inversion, singular value decomposition and adaptive damping together with Occam type constraining for model roughness. The new inversion method is implemented in the AEMINV program program, the graphical user interface of which is based on the DISLIN graphics library. Thus, it can be compiled and run on a variety of computer platforms without major modifications. The inversion method was found stable and computationally efficient. Because the model is one-dimensional, the results show apparent resistivity and depth although the inversion yields 2-D resistivity pseudo-sections. The AEM inversion using a two-layer model, however, gives a possibility to map separately the overburden conductance and basement resisitivity.
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Post-Tsunami Helicopter-Borne Electromagnetics Along the Coasts of Aceh, Indonesia
Authors B. Siemon, A. Steuer, U. Meyer and H. J. RehliAfter the earthquake and the tsunami-event on December 26, 2004, the Indonesian and German governments decided to set up a project that was dedicated to re-install the public life of the people in the coastal region of Aceh Province, Indonesia. As the tsunami waves caused large scale coastal salt-water intrusions and destroyed thousands of shallow drinking water wells, the focal point was the water assessment in coastal areas of Aceh about nine months after the tsunami.
The target areas are: Banda Aceh / Aceh Besar, the west coast between the towns of Calang (Aceh Jaya) and Meulaboh (Aceh Barat), and Sigli on the north-east coast. A helicopter-borne survey including five-frequency electromagnetics (HEM), magnetics and gamma-ray spectrometry was conducted by the BGR airborne group from August to October 2005. The northernmost survey area, Banda Aceh / Aceh Besar, comprises a 20 km by 50 km wide area that was surveyed within four weeks.
The HEM survey revealed coastal saltwater occurrences caused by the tsunami, deep saltwater occurrences up to several kilometres inland, and several potential fresh-water occurrences. Several requests for information on the geological/hydrogeological situation at sites for planned water wells were successfully evaluated.
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The Tellus Airborne Geophysical Survey of Northern Ireland
Authors D. Beamish and H. LeväniemiThis paper describes an airborne geophysical survey of Northern Ireland that is being conducted over a two year period. Measurements from a fixed-wing aircraft operating at 56 m include magnetic (gradiometer), radiometric and frequency-domain electromagnetic. The survey will complete over 80,000 line-km of coverage in the summer of 2006. The Phase 1 data, described here, comprise ~47,000 line-km obtained across the western and central areas of the province. The nature of acquiring geophysical data, at high resolution (200 m line spacing) in populated areas is distinct from that of other exploration contexts. The survey is being coordinated and conducted alongside a high public profile. The initial Phase 1 Tellus survey results have exceeded expectations. They have excited the interest of the planning, mineral and environmental communities.
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Semi-Automatic Approach to Deculture High Resolution Airborne Data
Authors M. Lahti, R. J. Cuss and A. DonaldThe problem of cultural noise places a severe limitation on the effectiveness of high-resolution airborne magnetic surveys. This paper presents a semi-automatic deculturing approach to enhance data from Northern Ireland surveyed in 2005. The high-resolution data (200m line spacing, 56 m flight elevation) acquired over this highly developed country is affected by cultural noise connected to various man-made sources potentially masking subtle geological information. The semi-automatic approach consists of two steps: 1) Automatic use of Pointer data to locate potential sources of cultural noise e.g. houses. 2) Manual refining of Pointer filtered data to clean remaining cultural noise and minimising geological distortion. The two-step approach allows a quick delivery of Pointer-filtered data where the level of cultural influence is significantly reduced. The final manual cleaning of remaining cultural noise is a slower process that results in high quality data with enhanced geological signature.
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Kimberlite Exploration at Low Magnetic Latitudes. Case Study at Serra da Canastra, Brazil
Authors P. T. L. Menezes and M. D. M. GarciaAirborne magnetic data from Serra da Canastra diamondiferous province is used to identify possible kimberlite signatures. Serra da Canastra is located in the central portion of the Brazilian territory within a low magnetic latitude area.
The interpretation strategy was based on the joint analysis of analytic signal and Euler deconvolution. A selected kimberlite target should have a roughly circular analytical signal anomaly coincident with a depth (0 – 200 m) and structural (N=2)
constrained Euler solution. The proposed approach led to ecognition of previously known pipes and new targets were evidenced.
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Geophysical Investigation of the Nasca Lines
Authors A. Weller, K. Hartsch, S. Rosas and G. ReppchenGeomagnetic mapping and electrical imaging are applied to investigate the soil structures in the vicinity of the geoglyphs in the Nasca desert (Peru) in comparison with areas of undisturbed soil in order to derive conclusions for a conservation of the lines. Both magnetic and geoelectrical method show significant anomalies caused by the lines but also structures of up to now unknown origin in the subsurface.
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New Results on Comparison of Different GPR Systems and Antenna Configurations at the Roman Site Carnuntum
Authors S. Seren, A. Eder-Hinterleitner, P. Melichar and W. NeubauerAbstract
Extensive test measurements were carried out over the last 3 years to evaluate different GPR systems, configurations and post-processing methods for archaeological prospection (Seren et. al. 2005). A new antenna by manufacture GSSI, the increasing of the submitted power of two antennas and improvements in filtering and visualization give new comparably results.
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2D and 3D Resistivity Tomography for the Detection of an Ancient Tunnel in Lavrion Area (Greece)
Authors C. Orfanos, G. Apostolopoulos and K. LeontarakisAt the archaeological site of Bertseko, in Laurion, the entrance of an ancient tunnel was found during archaeological excavations. After approximately 15 m the tunnel remains inaccessible – blocked with filled materials. 2d and 3d resistivity measurements were carried out in order to delineate the direction of the tunnel and to evaluate the effectiveness of resistivity imaging technique to detect such targets. Firstly, eight 2d resistivity profiles were carried out with the pole-pole array in a non-rectangular grid, in order to image a wider area, a greater depth, and to avoid several surface obstacles. Then the most promising area from the previous procedure was outlined and selected for analysis with 3d resistivity tomography (pole-dipole array) for better resolution. The field strategy adopted improves the delineation and the definition of the target and avoids the loss of valuable information with respect to the object under investigation. The integrated results from both 2d pole-pole and 3d pole-dipole profiles provide answers to archaeologist’s questions, delineate with great accuracy the direction of the tunnel and give rise to new aspects for the improvement of subsurface imaging and acquisition strategy.
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Target Detection Using Multi-Sensor Geophysical Surveys - Examples from Archaeological Surveys
Authors I. A. Hill, P. R. Fuller and C. LeechMulti-sensor survey systems can perform archaeomagnetic surveys more cost effectively than existing techniques, while simultaneously providing a denser, precise dataset with the potential for extending interpretation beyond simple imaging. The full benefits of application of existing potential field interpretation techniques to such data is yet to be realised.
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Combined Two-Dimensional Inversion of Four- and Three-Electrode Arrays Resistivity Data
More LessIn this paper, I suggest to use combined inversion of three- and four-electrode arrays data. Two-dimensional (2D) inversion results of Wenner (W), Schlumberger (S), Dipol-Dipol (DD), left- and right side pole-dipole (PD-L and PD-R) synthetic data and their combined inversion results are compared according to resolution and accuracy of the inverted models. Comparison results show that combined inversion of any two arrays data (eg. W+S, W+DD, PD-L+DD) sets give better resolution than the individual inversion of each corresponding arrays data set. However, inversion of PD-L, PD-R and and DD data sets jointly give better accuracy than the single use of any of these electrode arrays and combined inversion of any two electrode arrays.
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EM Induction Frequency Sounding - Estimation of Penetration Depth
Authors E. V. Balkov, M. I. Epov, A. K. Mastein and Y. A. MansteinOne of the most important characteristics of any geophysical instrumentation is the penetration depth. Present paper is devoted to description of the approach for estimation of the penetration depth for frequency sounding method. The approach takes into account the accuracy of the instrumentation and geoelectrical model as well. It is more accurate than traditional one that based on skin depth estimation. The investigations are carried out for two types of target objects for EMI frequency sounding device EMS developed by authors.
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Seismic – Acoustic Research on Identification of Some Archeological Buildings in the Submersible Zones
By A. SorinIn Romania, geophysical methods are normally used to estimate the distribution of cultural relics, before digging. Objects of archeological interest are usually located within a few meters of the surface.
Seismic –acoustic research was made with an specific equipment (“X-Star Full Spectrum Sub-bottom Profiler”)which works with frequency modulation in the range of 2-16 Hz. The vertical resolution of this system is better than 1 decimeter
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Marine Resistivity Measurements for the Foundation of Lavrion Old (1888) French Bridge
Authors G. Apostolopoulos, G. Amolochitis and S. StamatakiMarine resistivity measurements can give valuable information for the sedimentation under the sea bottom if the latter is not too deep. The Schlumberger configuration is preferred with its more efficient signal-to-noise ratio. Pole-Pole can give information which is less accurate in horizontal layering but offers deeper detection and possible positioning of lateral inhomogeneities in the event of great resistivity contrasts.
The old (1888) iron “French Bridge” in Lavrion Port suffers from corrosion by seawater and displacements and needs protection with the plan all to be mounted in a new substructure with the less visible changes. The marine resistivity survey gives valuable information to the engineer like where the old foundation lays, where to position the geotechnical drillings for additional information and outlines the environment of the structure to be built for the protection of the bridge.
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Gravity Survey in the Study of Vulnerability of Old Town
More LessGravity prospecting in urban areas can make possible to define vulnerability maps of territory, which are very useful in prevision and prevention of buildings crash risk especially in old town.
In this paper we show the results of two studies carried out to determine the shallow subsoil properties of two historical sites in Sardinia (Italy) by means the implementation of densities micro zoning map.
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Magnetic Properties of Archaeological Building Materials from Egypt
Authors A. Weller and A. El-BassionyThe magnetic properties of the building material are compared with the parameters of the embedding soil. The X-ray diffraction measurements performed on the selected samples had shown a higher magnetite content in the mud-brick samples compared to the low content in the soil samples. The measurements of the magnetic volume susceptibility for the selected samples had shown a measurable contrast between the mud-brick samples and the soil samples in Saqqara and Qantir.
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First Multi Beam and High Resolution Reflection Seismics Survey on the Tiber River Lower Course
Authors L. Orlando, M. Bernabini, A. Bosman, F. Chiocci and L. MacelloniAn integrated geophysical survey was carried out with the aim to investigate hydrodynamics, sedimentology, stratigraphy, pollution, archaeology and navigability of Tiber River (central Italy) lower course. Multibeam, side scan sonar and seismic reflection (Sparker and Pinger sources) data were acquired for a length of 80 km. The accurate location of the survey and the special processing used for the multibeam data gave us a digital elevation model of the river bed with a maximum resolution (in places) of 0.2 m.
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Focused Inversion of Gradient Magnetic Data from Saqqara North Cemetery, Egypt
Authors A. Weller and A. El-BassionyInversion of magnetic gradient data for archaeological purposes is performed using a focusing functional. The focused inversion of real magnetic gradient data from Saqqara proves to be successful by using the Minimum Gradient Support as a focusing tool. Information about the susceptibility contrast between the archaeological structures and the surrounding soil is found to be critical for the reliability of the inversion.
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