Correlation between aeromagnetic data rejection and geomagnetic indices

Predicting the rejection of aeromagnetic data would be a useful tool for aeromagnetic survey planning. To relate aeromagnetic survey requirements to geomagnetic activity monitoring and prediction, we analyzed the relationship between the rejection of aeromagnetic data as it is measured during surveys and the variations in existing geomagnetic indices. The magnetic data were collected at Canadian magnetic observatories during 2001 and covered the polar cap, auroral, and subauroral zones. The geomagnetic indices were global and local indices. The global indices included the Kp, ap, and Dst indices. The local indices were the three-component hourly ranges, the three-component maximum rate of change, and the Pc3 pulsation index. The goodness of fit was used to compare the results between the different indices at different locations. In general, there was some correlation between global geomagnetic indices and the rate of rejection of aeromagnetic data. Good correlation with a global index was obtained with the daily mean of the Ap index for a station located in the subauroral zone. The best correlation was obtained with local indices and particularly with the Pc3 index amplitude. From these results we conclude that forecasting Pc3 index amplitude would be a useful tool for planning aeromagnetic surveys.

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THE INTERPRETATION OF AEROMAGNETIC SURVEYS FOR HYDROCARBON EXPLORATION

The APPEA Journal ◽

10.1071/aj98030 ◽

1999 ◽

Vol 39 (1) ◽

pp. 494

Author(s):

I. Kivior ◽

D. Boyd

Keyword(s):

Spectral Analysis ◽

Sedimentary Basins ◽

Hydrocarbon Exploration ◽

Petroleum Exploration ◽

Magnetic Data ◽

Curve Matching ◽

Aeromagnetic Data ◽

Profile Data ◽

Aeromagnetic Survey ◽

New Approach

Aeromagnetic surveys have been generally regarded in petroleum exploration as a reconnaissance tool for major structures. They were used commonly in the early stages of exploration to delineate the shape and depth of the sedimentary basin by detecting the strong magnetic contrast between the sediments and the underlying metamorphic basement. Recent developments in the application of computer technology to the study of the earth's magnetic field have significantly extended the scope of aeromagnetic surveys as a tool in the exploration for hydrocarbons. In this paper the two principal methods used in the analysis and interpretation of aeromagnetic data over sedimentary basins are: 1) energy spectral analysis applied to gridded data; and, 2) automatic curve matching applied to profile data. It is important to establish the magnetic character of sedimentary and basement rocks, and to determine the regional magnetic character of the area by applying energy spectral analysis. Application of automatic curve matching to profile data can provide results from the sedimentary section and deeper parts of a basin. High quality magnetic data from an experimental aeromagnetic survey flown over part of the Eromanga/Cooper Basin has recently been interpreted using this new approach. From this survey it is possible to detect major structures such as highs and troughs in the weakly magnetic basement, as well as pick out faults, and magnetic layers in the sedimentary section. The results are consistent with interpretation from seismic and demonstrate that aeromagnetic data can be used to assist seismic interpretation, for example to interpolate between widely spaced seismic lines and sometimes to locate structures which can not be detected from seismic surveys. This new approach to the interpretation of aeromagnetic data can provide a complementary tool for hydrocarbon exploration, which is ideal for logistically difficult terrain and environmentally sensitive areas.

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

Earth Planets and Space ◽

10.1186/s40623-021-01466-5 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Takao Koyama ◽

Wataru Kanda ◽

Mitsuru Utsugi ◽

Takayuki Kaneko ◽

Takao Ohminato ◽

...

Keyword(s):

Hydrothermal Systems ◽

Magnetic Data ◽

Unmanned Helicopter ◽

Quaternary Period ◽

Aeromagnetic Survey ◽

Magnetization Intensity ◽

Line Spacing ◽

Normal Polarity ◽

The Cost ◽

Measurement Line

AbstractKusatsu-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.

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AN AUTOMATIC METHOD OF COMPILATION AND MAPPING OF HIGH‐RESOLUTION AEROMAGNETIC DATA

Geophysics ◽

10.1190/1.1440206 ◽

1971 ◽

Vol 36 (4) ◽

pp. 695-716 ◽

Cited By ~ 9

Author(s):

B. K. Bhattacharyya

Keyword(s):

High Resolution ◽

Magnetic Measurements ◽

High Sensitivity ◽

Positional Error ◽

Automatic Method ◽

Aeromagnetic Data ◽

Aeromagnetic Survey ◽

Machine Method ◽

Flux Gate ◽

Definition Of

An automatic method has been developed for compilation of digital aeromagnetic data. This method has been applied to the data obtained during a high‐sensitivity aeromagnetic survey over an area in the Precambrian shield of northeastern Ontario in Canada. With this method, all points of intersection between traverse and base lines are determined automatically and adjusted within the limits of positional error for minimizing differences in magnetic values at the intersections. Then the data are corrected for diurnal variation and leveled to tie the magnetic measurements together. Next, the resulting total field values are contoured with a machine method at a scale of 1:25,000. For such a scale, the minimum contour interval that can be used in the present area is two gammas. However, because of the accuracy of the method of compilation, with a larger scale, it is possible to trace one‐gamma contours. The maps thus compiled have been compared with published aeromagnetic maps of data obtained with conventional flux‐gate and proton‐precession magnetometers. The new maps are vastly superior to the old ones for delineating trends, patterns, and fine features of available detailed geological maps. This superiority is mainly due to the excellent definition of small amplitude anomalies, some of only a few gammas in magnitude, on the high‐resolution magnetic maps.

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Interpretation of airborne magnetic survey of Gabel Um Tineidba area, south eastern desert, Egypt

World Journal of Engineering ◽

10.1260/1708-5284.12.6.563 ◽

2015 ◽

Vol 12 (6) ◽

pp. 563-576

Author(s):

Tharwat H. Abdel Hafeez

Keyword(s):

Analytical Signal ◽

Eastern Desert ◽

Structural Features ◽

Geological Mapping ◽

Magnetic Data ◽

Magnetic Survey ◽

Aeromagnetic Survey ◽

Reasonable Proportion ◽

The Cost ◽

Airborne Magnetic

The study area is regionally covered by rock exposures ranging in age from the Precambrian to Quaternary. The aeromagnetic survey is a useful tool that help in geological mapping, providing information at a reasonable proportion of the cost of ground mapping. The reduced to the northern magnetic pole (RTP) map was separated into regional and residual magnetic component maps by the computed power spectrum of the magnetic data. The estimated mean depths of both regional and residual magnetic sources were found to be 2510 m and 383 m respectively. Also, two advanced techniques were used to analyze the depth magnetic data. These methods are analytical signal (AS) and source parameter imaging (SPI). The results of average depth estimates both methods (–950 m). These depth values were helped -to great extent- for define the direction of throw for the interpreted faults in the basement tectonic map. The statistical analysis shows that, most of the welldeveloped structural features are oriented mostly in the N-S, NNE-SSW, NW-SE and NNWSSE trending faults are considered the main trends affecting the distribution of the radioactive minerals.

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Structural features derived from a Multiscale Analysis and 2.75D Modelling of Aeromagnetic Data over the Pitoa-Figuil Area (Northern Cameroon)

10.5194/se-2020-135 ◽

2020 ◽

Author(s):

Voltaire Souga Kassia ◽

Theophile Ndougsa-Mbarga ◽

Arsène Meying ◽

Jean Daniel Ngoh ◽

Steve Ngoa Embeng

Keyword(s):

Multiscale Analysis ◽

Structural Features ◽

Magnetic Data ◽

Horizontal Gradient ◽

Aeromagnetic Data ◽

Near Surface ◽

Subsurface Structures ◽

Northern Cameroon ◽

Processing Techniques ◽

Geological Formations

Abstract. In the Pitoa-Figuil area (Northern Cameroon), an interpretation of aeromagnetic data was conducted. The aim of this investigation was first to emphasize lineaments hidden under geological formations and secondly to propose two 2.75D models of the subsurface structures. Different magnetic data processing techniques were used, notably horizontal gradient magnitude, analytic signal, and Euler deconvolution. These techniques in combination with the 2.75D modelling to the aeromagnetic anomaly reduced to the equator permit to understand the stratification of the deep and near surface structures, which are sources of the observed anomalies. We managed to put in evidence and characterize 18 faults and some intrusive bodies. According to Euler's solutions, anomaly sources go up to a depth of 5.3 km.

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Interpretation of aeromagnetic data over Abeokuta and its environs, Southwest Nigeria, using spectral analysis (Fourier transform technique)

Materials and Geoenvironment ◽

10.1515/rmzmag-2016-0018 ◽

2016 ◽

Vol 63 (4) ◽

pp. 199-212 ◽

Cited By ~ 2

Author(s):

Oluwaseun T. Olurin ◽

Saheed A. Ganiyu ◽

Olaide S. Hammed ◽

Taiwo J. Aluko

Keyword(s):

Spectral Analysis ◽

Fourier Transform ◽

Ground Level ◽

Magnetic Data ◽

Depth Range ◽

Aeromagnetic Data ◽

Southwestern Nigeria ◽

Southwest Nigeria ◽

Below Ground ◽

Magnetic Basement

AbstractThis study presents the results of spectral analysis of magnetic data over Abeokuta area, Southwestern Nigeria, using fast Fourier transform (FFT) in Microsoft Excel. The study deals with the quantitative interpretation of airborne magnetic data (Sheet No. 260), which was conducted by the Nigerian Geological Survey Agency in 2009. In order to minimise aliasing error, the aeromagnetic data was gridded at spacing of 1 km. Spectral analysis technique was used to estimate the magnetic basement depth distributed at two levels. The result of the interpretation shows that the magnetic sources are mainly distributed at two levels. The shallow sources (minimum depth) range in depth from 0.103 to 0.278 km below ground level and are inferred to be due to intrusions within the region. The deeper sources (maximum depth) range in depth from 2.739 to 3.325 km below ground and are attributed to the underlying basement.

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Reconnaissance geochemical and geophysical exploration for gold at Iri gold field, north central Nigeria

Scientia Bruneiana ◽

10.46537/scibru.v18i2.93 ◽

2020 ◽

Vol 18 (2) ◽

pp. 19-31

Author(s):

Ahmed Sidi Aliyu ◽

Nuhu Musa Waziri ◽

Hadiza Liman Mohammad ◽

Mohammed Abubakar Mohammed ◽

Apeh Aromeh Gideon

Keyword(s):

Gold Mineralization ◽

Structural Features ◽

Parent Material ◽

Geological Mapping ◽

Magnetic Data ◽

Geochemical Data ◽

Aeromagnetic Data ◽

Geophysical Exploration ◽

Rock Types ◽

Soils And Sediments

Reconnaissance geochemical and geophysical exploration for gold was carried out at IRI Gold field. Geological mapping was conducted and rocks, soils and sediments samples were collected. The outcome revealed rocks of the basement complex of Nigeria made up of mainly, Migmatite Gneiss, Older Granite and the Schist. The major lithology in the area is silicified sheared rocks and large quartz vein. Isolated occurrence of undifferentiated schist was found as parent material on which quartzite intruded possibly during a major geological activity. Shattering of the rocks left boulders and rubbles of quartzite all around two major ridges within the study area. The rocks have shown weak geochemical anomaly except in two locations were positive anomalies were observed and identified as target for further exploration. Gold veins are prominent in the area suggesting potential gold mineralization. Interpretation of the aeromagnetic data give the orientations of the structural features, the major structural trend in the area is NE-SW. The lineaments extracted from the magnetic data range in length from 46.43m to about 1251.66m. Most of the lineaments extracted from the area are subsurface within the quartz-mica and migmatites while some of them have surface expressions even though not clearly defined. These magnetic lineaments could be the contacts between two rock types of contrasting magnetic susceptibility or edges of structures that could be faults or intrusive bodies. Interpreted satellite data show several subsurface structures which could be hosts to gold mineralization in the area. Results of the geochemical analysis of rocks, soils and sediments were super imposed on the interpreted aeromagnetic data and similar geochemical and geophysical signatures were established. Index Terms: Gold mineralization, aeromagnetic data, geochemical data, schist belt, Nigeria

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Assessing Model Fit in Latent Class Analysis When Asymptotics Do Not Hold

Methodology ◽

10.1027/1614-2241/a000093 ◽

2015 ◽

Vol 11 (2) ◽

pp. 65-79 ◽

Cited By ~ 8

Author(s):

Geert H. van Kollenburg ◽

Joris Mulder ◽

Jeroen K. Vermunt

Keyword(s):

Sample Size ◽

Goodness Of Fit ◽

Latent Class ◽

Parametric Bootstrap ◽

Error Rates ◽

Asymptotic Distributions ◽

Type I ◽

Test Statistics ◽

P Values ◽

Global And Local

The application of latent class (LC) analysis involves evaluating the LC model using goodness-of-fit statistics. To assess the misfit of a specified model, say with the Pearson chi-squared statistic, a p-value can be obtained using an asymptotic reference distribution. However, asymptotic p-values are not valid when the sample size is not large and/or the analyzed contingency table is sparse. Another problem is that for various other conceivable global and local fit measures, asymptotic distributions are not readily available. An alternative way to obtain the p-value for the statistic of interest is by constructing its empirical reference distribution using resampling techniques such as the parametric bootstrap or the posterior predictive check (PPC). In the current paper, we show how to apply the parametric bootstrap and two versions of the PPC to obtain empirical p-values for a number of commonly used global and local fit statistics within the context of LC analysis. The main difference between the PPC using test statistics and the parametric bootstrap is that the former takes into account parameter uncertainty. The PPC using discrepancies has the advantage that it is computationally much less intensive than the other two resampling methods. In a Monte Carlo study we evaluated Type I error rates and power of these resampling methods when used for global and local goodness-of-fit testing in LC analysis. Results show that both the bootstrap and the PPC using test statistics are generally good alternatives to asymptotic p-values and can also be used when (asymptotic) distributions are not known. Nominal Type I error rates were not met when sample size was small and the contingency table has many cells. Overall the PPC using test statistics was somewhat more conservative than the parametric bootstrap. We have also replicated previous research suggesting that the Pearson χ2 statistic should in many cases be preferred over the likelihood-ratio G2 statistic. Power to reject a model for which the number of LCs was one less than in the population was very high, unless sample size was small. When the contingency tables are very sparse, the total bivariate residual (TBVR) statistic, which is based on bivariate relationships, still had very high power, signifying its usefulness in assessing model fit.

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Interpolation artifacts as a result of spatial aliasing: A case study of the airborne magnetic data set of southeastern Minas Gerais, Brazil

Geophysics ◽

10.1190/geo2019-0782.1 ◽

2020 ◽

Vol 85 (6) ◽

pp. B193-B205

Author(s):

Tobias Maia Rabelo Fonte-Boa ◽

Aline Tavares Melo ◽

Tiago Amâncio Novo

Keyword(s):

High Frequency ◽

Interpolation Method ◽

Acute Angle ◽

Magnetic Data ◽

Aeromagnetic Survey ◽

Data Set ◽

Linear Pattern ◽

Spatial Aliasing ◽

Geologic Interpretation ◽

Airborne Magnetic

Linear features at an acute angle with the flight direction are imaged as a series of aligned circular anomalies in the images of Area 15 aeromagnetic survey, which covered part of the Brazilian southeastern region. These features are interpolation artifacts, a recurring problem found in airborne magnetic images that cause problems for qualitative and quantitative geophysical-geologic interpretation. This imaging problem is attributed to spatial aliasing. By running simulations of magnetic data on a synthetic model, we have physically demonstrated that the interpolation artifacts from Area 15 are due to inappropriate survey design. Besides the most common expression of artifacts, we described a geologically noncoherent linear pattern as a new type of artifact. Supported by spectral analyses, we found that the Area 15 aliased spectrum is similar to geologic high-frequency magnetic features, which constitutes a motive for unearthing the correct geophysical signal. Thus, we made use of four techniques for removing the artifacts. The trend enforcement method partially improved the images, whereas the inverse interpolation method was ineffective, apparently because Area 15 data are severely aliased. The constrained coherence diffusion and multitrend gridding methods were able to significantly reduce the presence of artifacts. Despite the high-frequency attenuation, these tools adequately enhanced the magnetic trends and minimized the artifacts. Therefore, the improved images are better suited for reliable geologic interpretation.

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Spatial Clustering of Pedestrian Activity and the Built Environment Characteristics

Nano LIFE ◽

10.1142/s1793984418400056 ◽

2018 ◽

Vol 08 (02) ◽

pp. 1840005

Author(s):

Hao Zhang ◽

Li Yin

Keyword(s):

New York ◽

Built Environment ◽

Spatial Patterns ◽

Goodness Of Fit ◽

Spatial Clustering ◽

Poisson Model ◽

Urban Revitalization ◽

Policy Makers ◽

Global And Local ◽

The Impact

Promoting pedestrian activity has attracted increasing attention as an important strategy for the improvement of public health and urban revitalization. The impact on physical activity underpinned by built environment has been studied substantially; however, few studies had focused on the geographically varying relationships between pedestrian activity and the built environment characteristics. Built upon previous work, this study looks at the spatial patterns of pedestrian counts and the built environment contributors along two major streets in Buffalo, New York using global and local spatial autocorrelation tests and geographically weighted regression. Pedestrian generators, job density and land use mix are included as independent variables in order to study the impact on them due to the characteristics of built environment. Our findings suggest that (1) there are statistically significant clusters of street intersections with high pedestrian counts along the streets selected in our study; (2) there are some optimal sizes of clusters of pedestrian generators, which attract more pedestrians; (3) geographically weighted Poisson model helps to analyze the geographically varying relationships between the built environment and pedestrian activity with a more pronounced goodness of fit. This research contributes to the understanding of the spatial patterns of pedestrian activity and the geographically varying relationship between the built environment and pedestrian counts. Hopefully this research will help to guide and focus the minds of policy makers and urban planners alike to introduce street vitality through the modifications of the built environment, so as to improve the quality of life in their neighborhoods.

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