Airborne Gamma-ray Spectrometry Research Articles

Radioactive mineralization detection using remote sensing and airborne gamma-ray spectrometry at Wadi Al-Miyah area, Central Eastern Desert, Egypt

Band rationing, principal component analysis (PCA) and decorrelation stretch (DS) techniques of Landsat-8 with Sentinel-2 data successfully used in the discrimination of the lithological units and the surface structure features of Wadi Al-Miyah area in the Central Eastern Desert of Egypt. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were processed to identify the hydrothermal mineralized alteration zones related to the radioactive minerals. Airborne gamma-ray spectrometry (AGRS) has been used to determine the naturally occurring radioactive anomalous zones such as potassium (K), equivalent uranium (eU) and equivalent thorium (eTh) and to follow their spatial distribution in Wadi Al-Miyah area. The analysis of AGRS data revealed that, the study area owns a wide range of radioelement concentrations ranging from 15.5 to 98.4 μR/h, 5.9–37.1 ppm, 17.2–95.4 ppm, and 0.53%-10.29% of total count (TC), (eU), (eTh), and (K), respectively. The interpretation of the Radioelements Composite Image (RCI) successfully delineated the enrichment zones with radioelement concentrations within the alkali feldspar granite, biotite-muscovite schist, granodiorite and the hydrothermal alteration areas within the diorite of Gabal Al- Bakriyah. The results concluded that the integrated remote sensing and airborne AGRS data are promising in detecting the potential areas enriched with K, eU and eTh.

Integrated assessment and prospectivity mapping of geothermal resources for EGS in Brazil

Studies in Brazil related to geothermal resources have been carried out mainly by the National Observatory. Based on the results vast areas of Brazil have been delimited with a surface heat flow of over 60 mW/m2 and an excess temperature above 100 °C at depths between 3 and 6 km. The nature of the heat source and the mode of heat dissipation in these areas are largely unknown. Geothermal resources that might be associated with these areas can occur in hot sedimentary aquifers (HSA) and units of hot dry rocks (HDR) that are hosted, respectively, in intracratonic sedimentary basins and high heat producing granites (HHPG). The focus of our study is on finding resources of high enthalpy (above 150 °C) in HHPG, which regardless of their hydrological properties (porosity, permeability) could be considered as potential targets for enhanced geothermal systems (EGS). The structural provinces of Tocantins and Borborema were chosen as pilot regions based on both the indication of HDR and the wealth of open access georeferenced information. A comprehensive database was compiled and processed under GIS that includes geology, faults, soil typology, radiogenic heat, heat flow and geothermal gradient from wells, thermal spring locations, airborne gamma-ray spectrometry and magnetic surveys, terrestrial gravimetric surveys, and earthquake locations. In parallel, various critical factors were defined primarily to identify and characterize the most promising HHPG under insulating sedimentary rocks for EGS. These critical factors were grouped into three main categories labelled as: ‘thermal source’, ‘thermal insulation’ and ‘active pathways’. In the absence of exploratory data on existing EGS in Brazil these critical factors were used in this study along three separate work streams to develop a knowledge-driven model based on fuzzy logic for improving the knowledge on the prospectivity of geothermal resources. The developed model was further tested for its validation. The selected approach is expected to be applicable to mapping areas with EGS potential in other regions with similar geology and open access georeferenced databases.

Investigating the minimum detectable activity concentration and contributing factors in airborne gamma-ray spectrometry

Investigating the minimum detectable activity concentration and contributing factors in airborne gamma-ray spectrometry

Boolean and fuzzy logic operators and multivariate linear regression applied to airborne gamma-ray spectrometry data for regolith mapping in granite-greenstone terrain in Midwest Brazil

Recent studies have proposed several possibilities of combining K, Th and U airborne gamma-ray spectrometry channels to generate predictive algorithms maps. These algorithms can be used for mapping regolith in deeply weathered terrains with residual, erosion, and deposition surfaces helping to developed strategies to better understand the regolith landscape and to improve geomorphology interpretation, and to identify mineral exploration target sites for primary (bedrock or saprolite) or supergene (hosted in lateritic duricrust) ore deposits. With the goal to easily map the regolith, two mathematical procedures were used on airborne gamma-ray spectrometry data in GIS software, validated by fieldwork on granite-greenstone belts in Midwest Brazil: 1. airborne gamma-ray spectrometry and altimetric data integrated in Boolean and fuzzy logic allowed segregating the areas with ferruginous and manganese residual lateritic duricrusts from erosional surface with rocks and saprolite with 90% of accuracy (κBoolean = 0.69 and κFAPO = 0.66) and 2. airborne gamma-ray spectrometry and altimetric data integrated with weathering stages in multivariate linear regression (basic statistic) helped establish the regional weathering intensity index, with acceptable error (r2 adjusted >0.6 and p-value < 5%). These two modeling techniques provide useful, accurate, rapidly and complementary regolith maps and can be applied in large regions for preliminary interpretations.

Magnetic and gamma-ray spectrometric airborne geophysical data for investigating potential mineral resources and generating geoscientific knowledge in Colombia

The Servicio Geológico Colombiano has made available several airborne magnetometry and gamma-ray spectrometry datasets. The information was acquired in 15 blocks that cover approximately 520,000 square kilometers of Colombian territory, representing more than 850,000 linear kilometers of information. The data were collected along flight lines separated by 500 meters or 1000 meters, depending on the area, with sampling rates of 10 Hz (8 meters) and 1 Hz (80 meters) for the magnetometry and gamma-ray spectrometry data, respectively. The information is stored in 30 databases separated for each block and for each of the geophysical methods used. The Servicio Geológico Colombiano has provided a web portal that provides detailed specifications for each database and allows interested parties to see the terms and conditions to access the datasets and to check possible restrictions on access to information. To date, there is no geophysical database in Colombia with the coverage and resolution of these data sets, which will be very useful for geological research and research on potential mineral resources and to support geohazard monitoring, land-use planning and providing a baseline dataset for environmental monitoring.

Data-driven classification of bedrocks by the measured uranium content using self-organizing maps

Uranium is a naturally occurring element that can be found almost everywhere in rocks and soils throughout the earth's crust. One of its decay products, radon, is of gaining concern in recent years because this colourless, odourless, tasteless gas is proven to be responsible for many lung cancer cases each year. Analysing the spatial distribution of the uranium concentration in the ground surface can help predict radon hazard regions. In this study, two types of uranium measurements – airborne gamma-ray spectrometry (AGRS) and ground-based rock sample analysis via inductively coupled plasma mass spectrometry (ICP-MS) – are calibrated for the purpose. The two types of data with different sampling schemes are found to have a reasonable correlation to each other when using the mapped geology as categorical units. This finding confirms the feasibility of using geological maps as a first-order predictor to map uranium, and further radon, in a larger scale. We then apply the self-organizing maps (SOM) technique for a data-driven classification of rock types based on the measured uranium content. The presented study area is located at mid-Norway in the Trøndelag county, the same study will be performed in other regions across Norway where both types of measurements are in abundance.This study contributes to an on-going project to map radon hazard zones throughout Norway. While the radon hazard is defined by the indoor radon level which is affected by two folds of factors – geogenic (uranium-rich subsurface) and anthropogenic (dwelling type, indoor air exchange, etc.), our work aims to single out the geogenic factor. Comparing to the current national Radon Awareness Map of Norway (URL: http://geo.ngu.no/kart/radon/), where bedrocks were categorized by their likelihood of hosting elevated indoor radon, our approach utilizes measured uranium concentration of the ground which has a more direct link to the bedrock types.

Effects of environmental factors on the monitoring of environmental radioactivity by airborne gamma-ray spectrometry

This study describes and discusses the results of a 14 month-long campaign (April 2019 to June 2020) aimed at characterizing and quantifying the influence of environmental factors (cosmic rays, rainfall events, soil moisture and atmospheric radon) on airborne radiometric surveys, which are used for mapping the concentrations of potassium (K), uranium (U) and thorium (Th), or for monitoring the natural radioactivity in the environment. A large NaI(Tl) airborne spectrometer (4 down + 1 up detectors of 4 L) was installed at a height of 50 m on a meteorological tower to simulate an airborne hover at the Pyrenean Platform for Observation of the Atmosphere (P2OA) in Lannemezan. The continuous, high frequency acquisition of gamma-rays was accompanied by measurements of rainfall intensity, soil moisture content, atmospheric radon activity and meteorological parameters. A semi-diurnal cycle of apparent 232Th and 40K was observed and explained by atmospheric thermal tides. Both diurnal and seasonal cycles are also evident in the gamma-ray signal, mostly due to variations of soil moisture at these timescales with a maximum during summer when surface soil moisture (0–5 cm depth) is the lowest. An increase of 25% vol. of the soil moisture content, representing the range of variation between the end of summer (18% vol.) and the beginning of spring (43% vol.) leads to a decrease of gamma-rays in the K and Th window by the same amount. Conversely, these results illustrate the potential of using airborne gamma-ray spectrometry to monitor soil moisture at hectometer scales. The washout of radon-222 progeny during rainfall events influences the count of gamma-rays in the U window by adding an atmospheric component to the soil component. The amplitude of the signal increase in the U window varies with the precipitation rate and reaches 30% for an average event. By clear weather, atmospheric radon-222 volumic activity influences the count rate in the U window by about ±3.8% per Bq m−3, which translates into an influence of 148%/Bq m−3/kg Bq−1 (U). This comprehensive, multi-compartment approach is necessary to optimize and improve the processing and analysis of airborne gamma-ray spectrometry data for high sensitivity environmental studies. These results show the importance of environmental factors on the variability of gamma-ray spectrometry and the importance of taking them into account to accurately map radionuclides activities.

Airborne gamma-ray spectrometric technique for exploring potential hydrocarbon accumulations in Ar-Rassafeh Badyieh Area (Area-2), Syria

ABSTRACT The airborne gamma-ray spectrometry technique is newly practiced in Syria as an indirect approach for petroleum prospecting to detect structural traps favorable for possible hydrocarbon accumulations in Ar-Rassafeh Badyieh Area (Area-2). The thorium (Th) normalization technique is used in this approach to suppress regional geological influences. Three anomalous microseepage zones that are suitable as hydrocarbon occurrences were detected in Area-2 and identified by low residual potassium values and high uranium residual values relative to potassium values. The location of the first zone coincides with a productive hydrocarbon field, confirming the efficacy of the Th normalization approach with the microseepage model for detecting new probable hydrocarbon occurrences in Area-2.

Using air-borne gamma ray spectrometry and remote sensing data for detecting alteration zones around Wadi Saqia area, Central Eastern Desert, Egypt

This study presents the air-borne geophysical Gamma Ray Spectrometry data have been used for detecting the alteration zones related to hydrothermal activity. Areas enriched in potassium may indicate the existence of potassic alteration zone that is often associated with hydrothermal alteration accompanied by economic mineral deposits. The radioelements (K (%), eTh (ppm), and eU (ppm)) concentration distribution and the ratios of (K/eTh and K/eU) over the study area were presented. A Potassium Point anomaly map was obtained from the statistical treatment of the K (%), K/eU, and K/eTh spectrometric data. Anomalously High (X+3σ or more) areas were delineated and considered the most preferred areas for potassic alteration. If the maximum values exceed the (X+3σ) threshold, then (X+2σ) or (X+σ) is applied instead. Sixteen areas were delineated and suggested for the presence of potassic alteration. The F-Parameter of Efimov (K*(eU/eTh)) was also implemented as proved approach for delineating the most preferred areas for hydrothermal alteration. The result of the Potassium point anomaly mapping was compared to that of the F-Parameter technique that was used as reference for validating the results. The sixteen anomalous areas revealed from the Potassium point anomaly technique showed perfect correlation with the areas of highly anomalous F-parameter.Remote sensing study supported by field data and laboratory spectral analyses was also implemented in this study as another useful powerful cost-effective approach for alteration mapping. A field study was conducted; samples from the different observed alterations were collected. The spectral signatures of these samples were measured using the “ASD TerraSpec Halo mineral identifier” hand-held spectroradiometer. Spectral analyses were performed to obtain the spectral characteristics of the alteration zones of the study are. The end-members were identified through comparing the measured spectra against the United States Geological Survey (USGS) spectral library in ENVI v.5.1. software. The identified end-members include; Kaolinite, Sericite, Montmorillonite, Chlorite, Epidote and iron oxides. Subpixel Mixture Tuned Matched Filtering (MTMF) mapping technique was finally used for mapping the distribution of these end-members on ASTER nine Visible Near Infra-Red (VNIR) and Short Wave Infra-Red (SWIR) bands. The remote sensing data were validated as Semna gold mine and the identified alterations during the field study were successfully mapped by the remote sensing technique. Finally; Most of the delineated areas using the proposed Potassium point anomaly technique were also evidenced by the approached remote sensing technique. Moreover remote sensing suggested more alteration areas than did the gamma ray spectrometry data.

Calculation of natural external radiation dose rate for environmental impact assessment, case study: Abu Zenima area, Southwestern Sinai, Egypt

ABSTRACT The present article aims to assess environmental impact coming from terrestrial natural radionuclides, external gamma exposure dose radiation and the average effective annual dose value. The obtained data can be used to provide technical support for the social communication of nuclear energy bodies to understand the natural radiation background of the study area. To achieve the aim, 11271 measurements of 238U, 232Th and 40K were carried out using airborne gamma ray spectrometry for the study area. These measurements were used and converted in to specific activity for calculating the absorbed dose rate (D) and the annual effective dose (E) to infer the average annual effective dose value for the population of Abu Zenima area. The calculated specific activity of U238, Th232 and K40, absorbed dose rate, annual effective dose rate, collective dose and annual effective dose value for the population were mapped through Geographic Information System (GIS) using Arc map software version 10.5. The specific activity concentration of U238 ranged from 1 to 400 Bq/kg, Th232 ranged from 1 to 650 Bq/kg and K40 ranges from 1 to 4000 Bq/kg. The absorbed dose rate values ranged from 3.25nGy/h to 261 nGy/h. Annual effective dose rate values, varying from 21 to 9867 µSv y−1 with an average value of 172µSv y−1which is higher than the worldwide average value of 70µSv y−1 (for outdoor exposures from terrestrial radiation sources).The collective effective average dose (S), varied from 1.16 to 424.31 with an average value of 20.77 man mSv. Finally, average total population effective dose of Abu Zenima area ranged from 0.0013 to 0.0375 with an average value of 0.0129mSv. From all these results, it was concluded that Al Sahu, Al Nasb, Serabit El Khadim and Al Lehianlocalities have high background radiation.

Investigation and Analysis of Airborne Gamma Radiation Absorbed Dose Rate of Danjiangkou Reservoir

Airborne gamma-ray spectrometry is widely used in regional nuclear radiation surveys and environmental nuclear radiation pollution assessments. This paper aims at analyzing the status of nuclear radiation in the Danjiangkou Reservoir area by using airborne gamma spectrometry data. Mapping of the gamma radiation air absorbed dose rate in the study area was completed by using the Beck formula and divided into three different grades according to relevant national standards. Basing on the survey results, the main sources of high radioactive anomalies in the Danjiangkou Reservoir and surrounding areas were identified. Furthermore, a protection proposal was put forward to guarantee the water quality and safety of residents in the South-to-North Water Diversion Source.

Interpretation of aerospectrometric, aeromagnetic and geochemical data, Um-Alhuweitat basin area, Central Eastern Desert, Egypt

This study presents the analysis of airborne gamma-ray spectrometry and aeromagnetic data to delineate the distribution of the radioactive elements and determine their anomalous zones, subsurface structures controlled mineralized zones, and 3D magnetic inversion to give a full view of basement relief. According to statistical treatment of airborne gamma-ray spectrometry measurements, the highest values of potassium and equivalent thorium associated with Nakhiel Formation are 3.2% and 12.8 ppm respectively. Meanwhile, the equivalent uranium associated with phosphate beds attains 19.1 ppm. The spatial distribution of the relatively high concentrations of eU, eU/K and eU/eTh are recorded in adjacent areas in Upper Cretaceous deposits as > 12, 25 ppm and 5 ppm for eU, eU/K and eU/eTh, respectively.According to field measurements, the highest values of eU associated with phosphate beds and black Shale are 117 ppm and 20 ppm respectively. Meanwhile, the highest value of potassium associated with Quaternary sediments is 2.9%. Moreover, the highest value of eTh associated with Taref Formation is 16.2 ppm. The geochemical studies of collected samples from the anomalous zones showed the presence of secondary uranium in addition to rare earth elements. Meanwhile, the black shale trace elements are measured and showed high concentrations of tungsten. The magnetic data analysis is performed using tilt derivative and 3D magnetic modeling methods. Most of the deduced structures are trending in NW–SE, and NE–SW directions. The depths to the basement rocks are ranged from 0.475 km to 1.07 km below the ground surface.

Interpretation of geophysical data for iron ore detailed survey in Laje, Bahia, Brazil.

The transition zone between the Archean blocks, Jequié and Itabuna-Salvador-Curaçá, in the county of Laje, Bahia, Brazil, is potentially important for iron ore deposits of economic interest. This research investigates one of the eighteen anomalies defined by a previous integrated interpretation of geological and airborne gamma ray spectrometry and magnetic data in this transition zone. Its choice resulted from being located in an area with intense transcurrent shear and from the occurrence of pebbles rich in magnetite. Because of paucity of surface geological information, a ground-based geophysical survey added valuable information for the definition of a drilling program in the area. The survey consisted of two parts and followed up the aforementioned previous integrated interpretation of the Valença sheet. The first part consisted of one gravity and magnetic profile, which indicated a favorable site for additional investigation. The second part consisted of a detailed survey in the selected area with gravity, magnetic, and VLF-EM. The interpretation of the data of the geophysical methods allowed to delineate two zones in the area, both located at magnetic anomalies, gravity highs and relatively conductive parts. The two zones have a high potential for iron ore, because they present significant and correlated anomalies.

A log –barrier approach for airborne gamma-ray spectrometry inversion

The standard processing of airborne gamma-ray spectrometry (AGRS) data provides useful preliminary information to interpretation in several contexts, such as environmental studies, geological mapping, and analysis of mineral deposits. For optimal results, the acquisition conditions should be nearly constant, and the flight height should be uniform. However, abrupt changes in flight height (often originated from mountainous terrain) are common and lead to spurious variations and incorrect anomaly interpretation. Moreover, the commonly used corrections applied to radiometric data do not consider the effective sampling area of a survey, especially the overlap between successive fields of view. As a consequence, the concentrations estimates of potassium (K), uranium (eU), and thorium (eTh) are not sharp. A solution to deal with this problem is to compute the concentration from the AGRS data through an inversion algorithm. Inversion of AGRS data has shown to be an effective approach to suppress the significant overlap between successive fields of view. We introduce a logarithmic barrier approach for the radiometric inversion to avoid spurious negative values in the radioelement concentration models. We choose calibration ranges from Brazil and Canada to test the proposed methodology. We produced concentration models for K, eU and eTh and compared the standard approach model with the recovered model from both ranges. The predicted data from inversion of both calibration ranges are mostly consistent with the survey data, not over smoothing the data or fitting noise. The predicted data from inversion showed more consistency with the observed data than the one predicted from the standard procedure.

Retrieving geological units with unsupervised clustering of gamma-ray spectrometry data

Airborne gamma-ray spectrometry (AGRS) provides valuable insights for geological mapping, mineral exploration, geomorphological studies, and lithological differentiation. The interpretation of AGRS data is usually performed by skilled interpreters, requires visual acuity and is time-consuming. In this study, we used unsupervised clustering and object-based classification on the primary variables potassium (K), uranium (eU), and thorium (eTh) to automatically retrieve geological units in Mara Rosa Magmatic Arc – Goiás, Brazil, a well-studied area known by a gold district. We first cluster a color image composition (Red = K; Green = eTh; Blue = eU) using gaussian mixture models. We estimate the ideal number of classes to partition the image with the bayesian information criterion. Then, we performed a class separability analysis to identify and merge classes with low statistical separability. Finally, we used an object-based approach to reduce inconsistencies in the unsupervised classification map. To assess our approach, we compute the structural similarity index between the classification map and a reference geological map of the study area. The results show that our approach retrieved geologically meaningful regions in the AGRS data, reaching 0.94 of overall structural similarity with the geological map. Combining unsupervised clustering and AGRS data allows a better interpretation of the geological units into the same Complex or Groups.

Application of airborne radiometric surveys for large-scale geogenic radon potential classification

Background: Indoor radon represents an important health issue to the general population. Therefore, accurate radon risk maps help public authorities to prioritise areas where mitigation actions should be implemented. As the main source of indoor radon is the soil where the building is constructed, maps derived from geogenic factors ([e.g. geogenic radon potential [GRP]) are viewed as valuable tools for radon mapping.&#x0D; Objectives: A novel indirect method for estimating the GRP at national/regional level is presented and evaluated in this article.&#x0D; Design: We calculate the radon risk solely based on the radon concentration in the soil and on the subsoil permeability. The soil gas radon concentration was estimated using airborne gamma-ray spectrometry (i.e. equivalent uranium [eU]), assuming a secular equilibrium between eU and radium (226Ra). The subsoil permeability was estimated based on groundwater subsoil permeability and superficial geology (i.e. quaternary geology) by assigning a permeability category to each soil type (i.e. low, moderate or high). Soil gas predictions were compared with in situ radon measurements for representative areas, and the resulting GRP map was validated with independent indoor radon data.&#x0D; Results: There was good agreement between soil gas radon predictions and in situ measurements, and the resultant GRP map identifies potential radon risk areas. Our model shows that the probability of having an indoor radon concentration higher than the Irish reference level (200 Bq m-3) increases from c. 6% (5.2% – 7.1%) for an area classified as Low risk, to c. 9.7% (9.1% – 10.5%) for Moderate-Low risk areas, c. 14% (13.4% – 15.3%) for Moderate-High risk areas and c. 26% (24.5% – 28.6%) for High risk areas.&#x0D; Conclusions: The method proposed here is a potential alternative approach for radon mapping when airborne radiometric data (i.e. eU) are available.

Structural and hydrothermal alteration mapping related to orogenic gold mineralization in part of Kushaka schist belt, North-central Nigeria, using airborne magnetic and gamma-ray spectrometry data

This paper presents an interpretation of airborne magnetic and gamma-ray spectrometry data over a part of the Kushaka schist belt of Nigeria with a view to assess the sub-surface structural framework and hydrothermal alteration haloes that are related to orogenic gold mineralization in the study area. The geophysical analyses performed to improve the quality of the aeromagnetic data for better understanding of the subsurface geology were reduction to the equator, upward continuation, total horizontal derivative, analytical signal, source edge detection, tilt-angle derivative of total horizontal derivative. The analyses performed on the airborne gamma-ray spectrometry data were made on K/eTh, F parameter and deviation of ideal K values (Kd). Deep-seated, brittle–ductile shear/fracture zones with characteristic depth of 428.0–607.6 m and area extent of 15.5 km by 6.5 km that were delineated in the area coincide with beehive of artisanal miners exploiting gold deposits. In this study, subsurface geologic structures, specifically dykes/faults, that trend in the ENE–WSW direction constitute a first-order control on orogenic gold mineralization in the study area. The hydrothermally altered zones mapped in the area indicated they are structurally controlled and closely associated with orogenic gold mineralization. Apart from geologic structural evidences that are controlling orogenic gold mineralization, this study has indicated that hydrothermal alteration mapping is equally important for a promising orogenic gold mineralization mapping.

Assessment of radioactivity and geotechnical characteristics of soil foundation for suitability of safe urban extension using geospatial technology new Sahl Hasheesh Marin Port, eastern desert, Egypt

ABSTRACT In this study an appropriate investigation was carried out to assess the geotechnical parameters and possible health risks to verify the suitability of Sahl Hasheesh (SH) area for the urban extension using GIS techniques. For this purpose, eighty-three bore holes were drilled at depths 20 m below the ground surface. Laboratory tests were performed on representative soil and rock samples to determine their physical, mechanical and chemical characteristics such as: grain size distribution, chemical analysis, Atterberg limits and point load strength. Also, airborne gamma-ray spectrometry was used for finding the three-radioactive elements (K, U and Th) concentrations near the ground surface of the study area. These concentrations were analysed for specific activity concentrations of 238U, 232Th and 40K radionuclide’s to calculate the exposure dose rate (DR) and annual effective dose rate (AEDR). The annual effective dose rate ranges from 0.2 mSv/y to 4 mSv/y under permissible level, so the study area is radioactively safe. GIS techniques were used to produce many geospatial layers of radioactive and geotechnical properties and integrated all these layers to build the geospatial urban extension model. The urban extension model illustrated that the ideal and good zones were observed in most of the study area. But, the marginal to poor zones were observed in the northwest and central regions of the study area. This model will be useful in the management and development of the area under study. In addition, it will represent a database in the future to decrease the hazards impacts on the construction.

Application of Bayesian classifier to magnetic and gamma ray spectrometry data for targeting hydrocarbon microseepages

The search for new hydrocarbon resources is becoming increasingly complicated and expensive. Conventional geophysical methods, such as seismic, continue to focus on finding traps in deeper and more complex structures. To save significant amounts of both time and money, hydrocarbon microseepages may dramatically change the way we carry out hydrocarbon exploration by focusing more on searching petroleum deposits and by tracking their near-surface expressions. Hydrocarbon microseepages result in predominantly vertical long-term migration and it can be manifested with a number of near surface alterations such as formation of ferromagnetic minerals and modification of radioactive element concentrations in soil (potassium depletion and increase of the uranium concentration, in relation to the thorium content).In this study, airborne gamma ray spectrometry and magnetic data have been used in Hassi R'mel region (Algeria) to identify subtle variations in radioactive element concentrations and shallow magnetic anomalies induced by hydrocarbon microseepages. A Bayesian classification algorithm has been applied to characterize the residual magnetic and radiometric anomalies that occur above the known hydrocarbon reservoirs within the study area. Weights of evidence method was used to provide a quantitative measure of the spatial association between these anomalies and the mapped hydrocarbon accumulations. Most hydrocarbon areas were confirmed by the concurrent presence of the characteristic attributes of magnetic and radiometric anomalies, and those occurring outside the known hydrocarbon occurrences may point to yet unproven underlying hydrocarbon accumulations. The wells and drill core data, together with the blind wells available in the study area, validate the final results.

Precision spectroscopy of cesium-137 from the ground to 150 m above in Fukushima

After the Fukushima nuclear disaster in 2011, large amounts of radioisotopes (mainly 137Cs and 134Cs) were released into the environment. Various monitoring activities have revealed radiation on the ground both in local and wide areas; however, aerial dose variation in the vertical direction is poorly known. This paper presents the results of airborne gamma-ray spectroscopy of a contamination field in Namie, Fukushima, as measured from 0 m to 150 m above the ground by drone. We found that the gamma-ray dose rate measured at 100 m height is about seven times higher than that expected based on ground measurements, which is caused by two factors: (1) the integrated dose includes contamination of upward scattered 662-keV gamma rays and (2) radiation from 137Cs is vertically collimated because 137Cs is buried in the soil. We also propose a novel method to obtain the distribution of radioactive substances in the soil only through aerial mapping.