Integrative Geophysical Studies at the Novaya Kurya-1 Cemetery in the Kulunda Steppe

We outline the results of prospection studies at the Novaya Kurya-1 cemetery in the south of Western Siberia, using remote sensing methods such as aerial photography, ground-based magnetometry, high-precision aeromagnetic survey, electromagnetic profi ling, and electrotomography. Original techniques were used to construct relative relief maps, and an inversion of data from ground-based magnetic survey at various altitudes was carried out. The fi rst technique reduces the effect of natural relief, and highlights anthropogenic altitudinal anomalies, making the analysis of digital elevation models more effi cient. The second technique is helpful for assessing the thickness and depth of anomalous magnetic bodies or horizons, not only providing planigraphic information but enabling us to evaluate two- and threedimensional geometric properties of the detected objects. As a result of the analyses, at least 14 kurgans were identifi ed at the cemetery, six of which lack salient outward features. Structural details suggest that most of them date to the Early Scythian time (800–400 BC). On the basis of the interpretation of the results of highly effi cient prospection analyses using the UAV platform, offering the possibility of surveying a large area (about 25 ha), the boundaries of the site were determined. Several features were detected. To identify these, further studies are needed.

Airborne/UAV Multisensor Surveys Enhance the Geological Mapping and 3D Model of a Pseudo-Skarn Deposit in Ploumanac’h, French Brittany

Taking advantage of a multi-sensor (multispectral and magnetic) drone survey, we address the detailed geological mapping and modeling of a mineralization in its geological environment. We stress that these high-resolution data allow us to bridge the gap between field observations and a regional aeromagnetic survey. On the one hand, the combination of multispectral imagery with field geological observations enhances detailed geological mapping. On the other hand, the combination of field magnetic susceptibility measurement and their use in detailed to regional magnetic modeling, constrained respectively by UAV-borne and airborne magnetic surveys, allows deriving a model of the mineralization consistent across the scales. This is demonstrated in a case study in a complex polyphased magmatic-metamorphic environment on the coast of French Brittany. The target area hosts a pseudo-skarn mineralization, exhibiting an outstanding magnetic anomaly. The combination of remotely sensed and field data allows deriving a realistic conceptual and geometrical model of the magnetic mineralization in its geological environment, tightly constrained by field observations and measurements.

Aeromagnetic survey in Kusatsu-Shirane volcano, central Japan, by using an unmanned helicopter

Kusatsu-Shirane volcano is one of the active volcanoes in Japan. Phreatic explosions occurred in Mt. Shirane in 1983 and most recently, in 2018, in Mt. Motoshirane. Information on the subsurface structure is crucial for understanding the activity of volcanoes with well-developed hydrothermal systems where phreatic eruptions occur. Here, we report aeromagnetic surveys conducted at low altitudes using an unmanned helicopter. The survey aimed to obtain magnetic data at a high spatial resolution to map the magnetic anomaly and infer the magnetization intensity distribution in the region immediately after the 2018 Mt. Motoshirane eruption. The helicopter used in the survey was YAMAHA FAZER R G2, an autonomously driven model which can fly along a precisely programmed course. The flight height above the ground and a measurement line spacing were set to ~ 150 m and ~ 100 m, respectively, and the total flight distance was 191 km. The measured geomagnetic total intensity was found to vary by ~ 1000 nT peak-to-peak. The estimated magnetization intensity derived from measured data showed a 100 m thick magnetized surface layer with normal polarity, composed of volcanic deposits of recent activities. Underneath, a reverse-polarity magnetization was found, probably corresponding to the Takai lava flow in the Early Quaternary period (~ 1 Ma) mapped in the region. Our results demonstrate the cost-effectiveness and accuracy of using drone magnetometers for mapping the rugged terrain of volcanoes.

Investigation of Iron Ore Mineral Distribution Using Aero-Magnetic Exploration Techniques: Case Study at Pocheon, Korea

We present our aeromagnetic survey results from an investigation of the iron ore mineral distribution in Pocheon, Korea, in the west-central area of the Korean Peninsula. A manned aeromagnetic system using a helicopter for regional exploration and an unmanned aeromagnetic system using a multicopter for high-resolution exploration were used for the survey. The inversion results of the magnetic data confirmed the possibility of the existence of a new iron ore body. Drilling was carried out based on inversion results and drilling revealed amphibolite including iron ore, as indicated by a strong magnetic response. The position and depth of the iron ore were consistent with the interpretation results of the magnetic data.

Spline approximation of unequal aeromagnetic survey data with the use of UAV on spatially inhomogeneous networks when solving problems of archaeological exploration

The article discusses an approach to get a regular cube of data in context of aeromagnetic survey. It is based on spline approximation with nodes on an irregular grid in three-dimensional space. To construct approximation spline, information on measurement errors is additionally used, which makes it possible to reduce the number of parameters as opposed to spline interpolation. This approach was tested on experimental aeromagnetic data from archaeological site Ivanovka-I.

POWER SPECTRAL ANALYSIS OF RESIDUAL AEROMAGNETIC MAP OF SOKOTO BASIN, NORTH WESTERN NIGERIA

Aeromagnetic data obtained from a recent aeromagnetic survey of Sokoto Basin, northwestern Nigeria has been studied using Power Spectral (PS) analysis. The Sokoto Basin is an arm of the Iullemmeden Basin is situated between latitudes 10°30’’ N to 14° 00" N and longitudes 3° 30” E to 7° 00" E in the Nigeria national grid. The PS analysis was carried out to determine the depth to magnetic sources in the Basin. By splitting the study area into 16 spectral model blocks, the spectral probe of 27.5 by 27.5 km2 for each block was carried out respectively. The results of the PS analysis revealed two prominent magnetic source depth layers. Depths determination of the magnetic sources showed that the first layer has average depth of 0.28 km which is interpreted as shallow magnetic zones attributed to the intrusions of magnetic rocks into the sedimentary formation. The second layer has average depth of 1.86 km and was interpreted as the deep magnetic source representing the depth to magnetic basement. Hence the results show that the maximum thickness of the sedimentary layers to be 1.86 km is the limit of the depressions on the basement surface of the basin. Hence it suggests that exploration of hydrocarbon which would require a minimum sedimentary thickness of about 2.3 km as obtainable in the coasts of West Africa region is also not feasible.

OPTIMIZATION OF IDENTIFICATION MODELING IN THE STOCHASTIC METHOD OF TAKING INTO ACCOUNT THE TERRAIN IN THE INTERPRETATION OF AEROMAGNETIZATION

The results of studies aimed at optimizing the stochastic method of taking into account the terrain when interpreting aeromagnetic survey data are presented. The method is based on the consistent application of the method of empirical mode decomposition and the method of group accounting of arguments The results of a medium-scale aeromagnetic survey conducted in Eastern Siberia were used as actual data. It is shown that the preliminary classification of the studied territory by the nature of the relief and the magnetic field strength allows us to determine the components of the magnetic field that correlate with the relief within the selected classes. To assess the quality of correlation dependencies, the ratio of the standard deviation of the models to the variance of the magnetic field amplitudes of the analyzed frequency component were used. This allows us to compare models with different statistical characteristics of the anomalous magnetic field and divide the components into correlated and uncorrelated with the terrain. The results obtained confirm the possibility of the existence of strong correlational relationships between the magnetic field and the relief in a certain range of spatial frequencies and offer specific methodological methods for applying this stochastic approach to reducing the magnetic field in the areas of the development of platobasalts.