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NSG2022 3rd Conference on Airborne, Drone and Robotic Geophysics
- Conference date: September 18-22, 2022
- Location: Belgrade, Serbia & Online
- Published: 18 September 2022
1 - 20 of 22 results
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Mapping an Igneous Dike in Carbonate Rocks by Drone-Borne Magnetometry
Authors F. Accomando, A. Bonfante, M. Buonanno, G. Florio, J. Natale and S. VitaleSummaryMagnetic method plays an important role in different fields of application. In the past decade, the introduction of drones and the development of miniaturized, lightweight magnetic sensors opened new data acquisition possibilities. In fact, the drone-borne magnetometry allows collecting magnetic datasets characterized by a uniform areal coverage and good resolution, representing an intermediate solution between the classical ground and high-altitude airborne prospections. Moreover, drones allow to reduce costs, time, and risks, with respect to other acquisition techniques, and allow performing high resolution surveys over places of difficult access. In this study, we conducted a drone-borne magnetic survey, on the southwestern slope of the Mt. Cesima ridge, northeast of Roccamonfina volcano. Here, within the active quarry of Taverna San Felice (Presenzano), we performed a magnetic mapping of an igneous dike intruded in Mesozoic carbonates. The results, integrated with field and drone-based structural data, as well as the geological mapping, helped to constrain the geometry of this magmatic dike and the distribution of its pyroclastic deposits, shedding light on an impressive example of interaction between volcanism and tectonics in the southern Apennines.
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Assessing Quantitatively Interpretable Zones From 1D Forward Modelling Aem Inversion Models
Authors W. Deleersnyder, D. Dudal and T. HermansSummaryThe inversion of time-domain AEM data with full 3D inversion requires specialists’ expertise and a huge amount of computational resources, not readily available to everyone. Consequently, quasi-2D/3D inversion methods are prevailing, using a much faster but approximate (1D) forward model. The question remains whether the obtained inversion results are reliable and can be interpreted quantitatively. We propose an appraisal tool for quasi-2D/3D methods that indicate zones in the inversion model that are not in agreement with the multidimensional (2D/3D) forward model and therefore, should not be interpreted in a quantitative fashion.
The image appraisal step only requires one full 2.5D or 3D forward and one multidimensional Jacobian computation on a coarse mesh to compute a so-called normalized gradient. Large values in that gradient indicate model parameters that do not fit the true multidimensionality of the observed data well and should not be interpreted quantitatively. We demonstrate our method on a real AEM survey in a salinization context, revealing problematic zones in the fresh-saltwater interface. Interestingly, the problematic zones are not necessarily at larger depths, but where the interface is changing. The advantage of our approach is that all computations are feasible on a single laptop.
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Investigating the Integration of Neural Networks in Least-Squares Method for Airborne Electromagnetic Data Inversion
Authors M.R. Asif, P.K. Maurya, J.J. Larsen and A.V. ChristiansenSummaryAirborne time-domain electromagnetic surveys produce large datasets that may contain thousands of line kilometers of data. The inversion of such large datasets becomes a computationally expensive process due to the repeated calculations of the forward model data and the partial derivatives for solving the least-squares inverse problem. To improve the computational efficiency of the inversion process, we use neural networks to compute the forward model data and the partial derivatives for a broad range of resistivity structures and flight altitudes for an airborne setup. Experiments show that the integration of neural network based forward data modelling and partial derivative calculations within the inversion framework opens the possibility of faster inversions with little to no loss in inversion precision.
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Progress Towards a Drone-Based Transient Electromagnetic System, Some First Results
Authors M. Panzner, N.S. Nyboe, G.H. Skurdal, K.S. Mohr and A.A. PfaffhuberSummaryIn this paper, we present some first development towards a drone-based transient electromagnetic (TEM) system that can fill the gap between large scale airborne electromagnetic surveys and ground-based resistivity measurements. Such a system can aid geotechnical ground investigations prior to small and medium size infrastructure projects like tunnels, bridges, or large buildings. We present a downsized TEM system that can potentially be carried by a large drone. Data acquired with this system over a known site in Central Norway are compared to conventional airborne TEM data acquired with the much larger SkyTEM304 system at the same geographical location. We also compare and analyze inverted subsurface resistivity models from the two datasets and demonstrate that it is possible to recover similar subsurface resistivity information with a significantly smaller system, that uses state state of the art transmitter and receiver electronics combined with digital data recording.
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Deep Convolutional Auto-Encoder for Automated Processing of Airborne Time-Domain Electromagnetic Data
Authors M.R. Asif, J.J. Larsen, E. Auken and A.V. ChristiansenSummaryModern airborne electromagnetic surveys produce large datasets that may contain thousands of line kilometers of data. In urbanized areas, parts of these data are often disturbed due to couplings to infrastructure and must be culled before inversion for reliable geological interpretation. As of today, the process of identifying couplings is generally a manual task, which require specialists to examine and process the data subjectively. These subjective workflows are difficult to reproduce and relatively time-consuming. To eliminate the complex data processing workflows, we propose an algorithm based on a deep convolutional auto-encoder to identify coupling in the data in an automated manner. The autoencoder is configured to encode the TEM data in a latent space. The encoded data is trained to decode the encodings to reconstruct the input data. If clean data are observed by the auto-encoder, the reconstructed output will have low error to the input. However, when dealing with couplings, the reconstruction error is elevated, indicating a non-geologic anomaly. We show that the proposed approach displays high quality data processing within a fraction of a second, and is a significant step towards a complete automated processing and inversion workflow, greatly reducing costs and increase reliability of airborne datasets.
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Fracture Network Analysis of the Balmuccia Peridotite by Drone-Based Photogrammetry
Authors N. Menegoni, A. Greenwood and G. HetényiSummaryA drone-based Digital Outcrop Model (DOM) of the Balmuccia Peridotite (Ivrea-Verbano Zone, Italy) was developed to quantitatively characterize the rock discontinuity network and to aid interpretation of high-resolution seismic datasets that cross the drilling target of the Drilling the Ivrea-Verbano zonE (DIVE) Phase 2 project. Thanks to the photograph resolution (3 cm/pixel), the drone on-board Real Time Kinematic-Global Navigation Satellite System, and the Ground Control Points, it was possible to develop a high resolution and accurate DOM. Eight sets of discontinuities (e.g., fault, fracture, layering) are identified, their length distributions are defined, and the areal intensity (P21) and spatial variations estimated. The orientations of the discontinuity sets agree with previous field-based studies indicating a good validity of DOM-analysis. It shows that the N-S vertical set (pyroxenite layers marking the foliation) is the most frequent, the E-dipping set has the highest size, and the two vertical sets trending ca. WNW-ESE and WSW-ENE (trace of fault system) have the lowest frequency and size. Moreover, the dataset shows that the highest P21 is located closer to the inactive quarry and to the Peridotite-Mafic complex contact. These findings will have major implications for the interpretation of the high-resolution seismic data of the Balmuccia target.
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Best of Both Worlds: Innovative Environmental Monitoring Methods Using Multispectral Uav and Satellite Data
Authors B. Haske, T. Rudolph, B. Bernsdorf and M. PawlikSummaryThe protection of natural and near-natural ecosystems is becoming increasingly important in today’s society. Due to centuries of mining, industrial, agricultural and infrastructural use of soils and waters in large parts of the world, their condition has deteriorated almost continuously because of human activity. The increase in extreme weather events caused by climate change has further intensified this development in recent years. In order to preserve or, if possible, to improve the near-natural areas, a large-scale but also precise environmental monitoring is necessary, which cannot be achieved by measurements and observations on site (in-situ) alone. In addition, the change in the availability of raw materials and therefore the different requirements on mining projects make it necessary to implement integrated monitoring systems.
The use of currently available methods of remote sensing and photogrammetry shows promising approaches to close the existing data gaps both in spatial and temporal extent. For this purpose, a three-stage monitoring system, consisting of satellite, UAV and in-situ data, has been developed and used in various projects at the Research Center of Post-Mining.
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The Results of Experimental and Methodological Work With the New Uav-Tem Technology on Lake Baikal
Authors Y. Davydenko, S. Tereshkin, A. Bashkeev, S. Iakovlev, M. Shkirya, A. Parshin and M. PersovaSummaryNowadays magnetic and gamma surveys using UAV technologies are widely used in the practice of geological exploration. However, until now electromagnetic sounding in the UAV version is practically not used, but is very promising. In this paper, we consider the results of testing the UAV-TDEM technology. This technology is a time-domain transient electromagnetic sounding on a lightweight UAV. A measuring system with an inductive sensor (receiving loop) is towed by a UAV, and a galvanically grounded power transmitter is on the ground and connected to a pulse generator. The testing place was not chosen by chance: Baikal Lake is a unique geological formation with a rather simple one-dimensional geoelectric model at first glance: a fresh water layer with a resistivity of about 200 Ohm m, under which there are low-resistivity bottom sediments.
3D modeling, performed taking into account bathymetry, has shown that under a water layer with a thickness of 200–300 m a high-resistance objects are found in conductive sediments to a depth of at least 200 m. Some of them are extensions of coastal geological structures. As a result, the depth of the UAV-TDEM technology in these geoelectric conditions is estimated of about 500 m.
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A New Data Acquisition System for Uav-Borne Vlf-Lf Measurements. Two Case Studies in Sweden
Authors M. Bastani and H. JoahanssonSummaryIn the frame of an EU-funded project a data acquisition system has been developed to measure the electromagnetic (EM) signal from the distant radio transmitters in the frequency range 10–350 kHz onboard an Unmanned Aerial Vehicle (UAV). The system is composed of a data logger and a 3-component induction coil sensor, mounted in a costume-built bird, and records the magnetic field components of the EM signal in three perpendicular directions. The system is hung 10 m below the UAV. We present two case studies in Sweden where the system has been tested and utilized to map the electrical resistivity variations. The first area was located close to an iron ore mine and the resistivity maps from the recoded data revealed a very good correlation with the underlying structures such as landfills, glacial sands, and pits. The second area was near an abandoned gold mine where the conductive sulfide mineralization residing in greywacke rocks are mapped as low-resistivity zones. A semi-airborne test was also conducted using a grounded electric dipole transmitter at frequencies down to 1 kHz. The collected semi-airborne data are of high quality and show signal to noise ratio.
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Mapping of Quick Clay Using Frequency-Domain Helicopter Em (Hem) in Orkdal Valley, Norway
Authors V.C. Baranwal, B. Larsen, I. Solberg, S. Gradmann, Y. Liu and J.S. RønningSummaryQuick-clay landslides are reported from different parts of the world, specially from Nordic countries, Canada, and Russia. Quick clay is mainly observed in marine clay areas. Various geophysical methods can help mapping of potential quick-clay deposits. NGU uses frequency-domain helicopter EM (HEM) and electrical resistivity tomography (ERT) to map potential quick-clay areas in Norway.
Orkdal valley in Norway is characterized by thick deposits from the ice age and deglaciation period. In 2021 NGU, in collaboration with NVE, collected HEM, ERT and ground penetrating radar (GPR) data from Orkdal valley for quick-clay mapping. We present subsurface resistivity models obtained from full 3D inversion of HEM data and its comparison with ERT along one profile. There is a general good correlation between ERT and HEM data, and also with a geotechnical drilling profile from an earlier mapped quick-clay hazard zone.
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Deep Targeting With Airborne Electromagnetic Surveys
Authors P. Gisselø, P. Daoultzis and E. SmartSummaryA powerful airborne electromagnetic system is the optimal choice for deep targeting of conductive bodies. Variations in the receiver induction coil specifications can be used to optimise the system for various purposes. Providing the possibilities for maintaining focus on optimal depth penetration by using the high area and low frequency coil or choosing the lower area and high frequency coil to obtain more surface near details and a more cost-effective survey.
The survey around Skouries, Greece, was conducted with a setup that allowed for more surface near resolution and higher acquisition speed. The survey results have clearly mapped the well know Skouries deposit as a conductive body and has at the same time indicated two possible satellite conductive bodies. The Okiep Copper Project, South Africa, was flown with a setup optimized for maximum depth penetration. A series of late-time electromagnetic targets have been identified. The first target has been drilled and the drillhole has successfully intersected a pyrrhotite-chalcopyrite mineralisation.
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Using Multiple Points Statistics in Indian Wells Valley, California to Estimate the Aquifer Storage Capacity
Authors T.B. Rasmussen and M.L. GulbrandsenSummaryThe recently finalized Stanford Groundwater Architecture Project (GAP) was designed to define the optimal workflow using advanced geophysical and computational methods for the development of hydrogeological conceptual models (HCMs) in California. The basin in Indian Wells Valley (IWV) was one of the pilot areas in the project and is categorized by the California Department of Water Resources as subject to critical conditions of overdraft and is categorized as a High Priority Basin under the California Sustainable Groundwater Management Act. Being able to map the potential aquifers in the IWV is therefore of great importance. To do this, Multiple Points Statistics (MPS) were used. The target of the MPS simulations was to locate potential local aquifers within a hydrogeologic zone mainly consisting of clay, and in turn to estimate their groundwater storage capacity. This was done by combining Airborne Electromagnetic data, borehole information, and geological background knowledge, and to compute 75 extensive 3D models of the area. Based on the simulated models, we could point out areas with increased probability of being local aquifers and compute their potential storage capacity.
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Securing Waterpower Production Using Airborne Gpr
Authors J. Friborg, J. Emilsson, E. Nordström and J. GustafssonSummaryHydropower is an essential source of renewable energy. To secure power production in cold climates, it is of vital importance to continuously collect information regarding ice build-up around the power plant. The amount of ice, and the quality of the same, can cause significant loss in power production. Ice loads on dam structures are complicated to model and predict without plenty of data points. Traditionally this is performed by foot and using drilling, which is not only a safety issue but usually delivers too few data points to obtain an accurate model of the ice load. With recent developments of airborne GPR equipment, hazardous areas can be investigated safely and efficiently. Furthermore, in comparison to traditional methods airborne GPR collects vast amounts of data points, thus helping create better and more stable models for ice-loads. This paper covers a study from around a hydropower plant in northern Sweden. The study discusses the pros and cons of using air borne GPR equipment for securing hydropower production in cold climate areas.
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Interrogating the Subsurface of the Srebrenica Magmatic Complex: Airborne Em Survey as Mineral Exploration Targeting Tool
Authors P. Gisselø, A. Mišković, M. Kelly and S. VauganSummaryThe Srebrenica Magmatic Complex is the western member of the Podrinje Metallogenic District that straddles the Bosnian-Serbian border and includes the Serbian Cer and Boranja mining districts, collectively the northwesternmost extensions of the Serbo-Macedonian Metallogenic Province (SMMP). The SMMP mainly hosts ore deposits of Paleogene to Neogene age, although some Mesozoic and Late Palaeozoic deposits are also present. Available radiometric ages indicate the onset of magmatism around 30 Ma in the southern part of the province along the NNE-SSW trending Cer-Zvornik-Srebrenica line.
The variable geological structures present here highlighted the need for the deployment of an airborne system that would be able to map the structural details and also deliver a good depth of penetration. These requirements are fulfilled by the SkyTEM306HP system operated at 12.5 Hz repetition frequency. The airborne survey results have been evaluated together with geochemical soil sampling and structural analyses to perform the target generation at the three prospective zones defined as Olovine, Brezani and Chumavichi for both the surface near and deeper seated targets.
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Uav-Tem Data Inversion With S-Plane Method to Highlight Coastal Geological Structure of Lake Baikal
Authors Y.A. Davydenko, V. Hallbauer-Zadorozhnaya, A.S. Bashkeev and A.V. ParshinSummaryThe abstract presents the results of the experimental work of the TEM with the use of drones, carried out at the Bolshoe Goloustnoye site on Lake Baikal. Baikal is a unique geoelectric polygon, where low-resistivity lacustrine sediments are located under a relatively isotropic water body. The upper part of the sedimentary sequence is represented by diatomaceous silt with high conductivity, the lower part is represented by denser clayey sediments. High-resistivity inclusions are found in both layers: gas hydrate plates and methane deposits.
The fused instrumentation complex consist of: EGI-500 - generator of bipolar current pulses, Mars 4.0 which is a multi-channel electrical prospecting potential difference recorder, PDI-50 – a reciever loop, SibGIS UAS - unmanned 6-rotor aircraft with a payload up to 10 kg.
The16 profiles were carried out. Six profiles were located parallel to the electrical line AB, nine are perpendicular to AB.
The interpretation of the TEM data was interpreted using version, which will allow one to trace the change in the apparent longitudinal conductivity with depth. On the sections, a high-resistivity layer is clearly distinguished, corresponding to the water of Lake Baikal and sedimentary deposits, composed by several blocks of low resistivity.
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A Semi-Airborne Em Study of the Hope Ore Deposit (Namibia) Using a Drone-Based Concept
Authors P. Kotowski, M. Becken, A. Thiede, G. Symons, J. Schmalzl and S. UedingSummaryUnmanned aerial vehicles (UAVs) are ideally suited as carriers for passive receiver instruments. To demonstrate the capability of UAVs for semi-airborne electromagnetic (EM) application, we have conducted a drone-based semi-airborne EM survey at the Hope ore body (Namibia), a well-explored volcanogenic massive sulfide deposit. The conductive deposit is embedded in a resistive sediment and is a perfect case study target for methods that are sensitive to electrical conductivity. The semi-airborne method differs from conventional airborne EM methods by the installation of powerful ground-based transmitters facilitating greater penetration depths. By determining magnetic transfer functions and estimating 2D subsurface conductivity models on that basis, we aim to image the characteristics of the deposit.
We have determined consistent transfer functions up to 2km distance to the employed transmitters at frequencies ranging from 32Hz to 4kHz. However, there remain challenges such as UAV-related EM noise limiting the data quality. It was possible to estimate conclusive inversion models, map the extent of the conductive target successfully, and track down the ore body to a depth of more than 300m. It is yet unclear to which depth the Hope deposit can be resolved — this would require an extension of the survey.
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Combining Boreholes and Airborne Em Models for Automatic Generation of Hydrostratigraphic Model Realizations
Authors A.V. Christiansen, N. Foged and Z. RawlinsonSummaryDetailed structural information of the subsurface is fundamental for the development of hydrological models. The hydrostratigraphic modelling concept (HSM) for unconsolidated sediments is a concept which compiles realizations of 3D hydrostratigraphic models. The overall purpose is to generate an ensemble of models that honour the input data in an objective, fast, and well-documented manner. This makes it possible to quantify the structural uncertainty and thereby the uncertainty of model predictions based on this ensemble. The structural information in HSM is derived from geophysical models (here SkyTEM) combined with lithological borehole information. However, some parts of the model area do not have SkyTEM coverage (noise/towns), which results in resistivity information gaps. Geostatistical methods are used to fill these data gaps and to incorporate relevant uncertainty measures in the construction of the ensemble of hydrostratigraphic models. We show the results of using the HSM on a large SkyTEM survey in New Zealand. It showcases a method to quickly and objective translate geophysical data into hydrostratigraphy (including uncertainty) by incorporating lithological borehole information as a guide for the translation. The uncertainty is obtained through the ensemble of equally probable models.
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Using The “Triad” of Uav-Tem, Uav-Magnetic Prospecting and Uav-Gamma-Spectrometry: Case of Prospecting for Blind Ore Deposits
Authors A. Parshin, M. Gatilov, Y. Davidenko, A. Bashkeev, N. Snegirev and A. MilgunovSummaryIn order to successfully prospect for new deposits, in most cases it is necessary to use a set of geophysical methods that allow both studying the surface, and creating models of the deep structure of the near surface part of the earth’s crust. The classic universal combination is the «triad» of methods “magnetic prospecting+gamma-spectrometry+electromagnetic prospecting”, this option is used in most geophysical systems based on manned helicopters. In recent years, magnetic prospecting and gamma survey methods have already been widely used in the UAV version, so UAV-based electromagnetic soundings are of maximum interest at this stage of geophysics. In this paper, we consider a case of combining all three UAV-based methods in the case of prospecting for blind deposits of sandstone-type uranium, with special attention being paid to the use of the current version of SibGIS UAV-TEM system for time-domain electromagnetic sounding, which is significantly improved compared to the first prototypes. According to the authors, this case proves that unmanned systems, which allow performing geophysical surveys with a set of methods at low altitudes and with precise terrain drape, make it possible to almost completely abandon ground-based surveys, at present - and in the case of transient electrical prospecting too.
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Unexpected Effects of Ip Distorsion in Aem Survey for Hydrogeology
Authors A. Menghini, A. Viezzoli and I. FernandezSummaryThis case study shows how the IP distortions can occur also in areas, which are usually less likely to present IP effects. Besides the chargeability distribution (that may not be directly relevant, e.g., for aquifer mapping), the correct handling of IP distortion usually translates into a more accurate resistivity modelling, hence in a better geological/hydrogeological modelling. The results obtained modelling IP both fit better the known geological setting and are numerically more robust. Potential IP distortions should not be ruled out a-priori from virtually any AEM survey.
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Pushing Exploration in the Pyrite Belt Around Aem
Authors A. Menghini, I. Fernandez and A. ViezzoliSummaryWe present three case studies focused around the Xcite AEM system, and its applicability to different targets in the Pyrite belt. Gravity always played a crucial role, later accompanied by EM methods. Modelling IP effects and extending depth of exploration below conductive cover are some of the challenges that need to be met for more successful applications of AEM. Exploring in the region also requires acknowledging the often large variability of physical properties associated to the mineralizations.
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