Locating magnetic contacts: A comparison of the horizontal gradient, analytic signal, and local wavenumber methods

2000 ◽  
Author(s):  
Jeffrey D. Phillips
Keyword(s):  
Analytic Signal ◽  
Horizontal Gradient ◽  
Local Wavenumber

scholarly journals Estimation of Magnetic Contact Location and Depth of Magnetic Sources in a Sedimentary Formation

2019 ◽  
Vol 66 (1) ◽  
pp. 27-37
Author(s):  
A.A Alabi ◽  
V Makinde ◽  
A.O Adewale ◽  
J.O Coker ◽  
T.J Aluko
Keyword(s):  
Source Parameters ◽  
Signal Amplitude ◽  
Analytic Signal ◽  
Horizontal Gradient ◽  
Southwestern Nigeria ◽  
Region Data ◽  
Basement Depth ◽  
Anomaly Map ◽  
Local Wavenumber ◽  
Deep Sources

AbstractThe aeromagnetic data of Idogo, Southwestern Nigeria, have been used to study the lithology and to determine the magnetic source parameters within Idogo and its environs. Idogo lies between latitudes 6°30′N and 7°00′N and between longitudes 2°30′E and 3°00′E. The magnetic anomaly map, the regional geology, the analytic signal and the local wavenumber were used to identify the nature and depth of the magnetic sources in the region. Data enhancement was carried out to delineate the residual features relative to the strong regional gradients and intense anomalies due to the basin features. The estimated basement depth using the horizontal gradient method revealed depths ranging between 0.55 km and 2.49 km, while the analytic signal amplitude and local wavenumber methods estimated depth to the magnetic sources to range from 0.57 km to 4.22 km and 0.96 km to 2.43 km, respectively. Depth computations suggested the presence of both shallow and deep sources. The total magnetic intensity values ranged from 3.1 nT to 108.3 nT. The area shows magnetic closures of various sizes in different parts of the area trending West, with prominence at the centre and distributed East–West.

Magnetic gradient techniques on digitized aeromagnetic data of Ibadan area, south-western Nigeria

2013 ◽  
Vol 5 (3) ◽  
Author(s):  
Biodun Badmus ◽  
Musa Awoyemi ◽  
Olukayode Akinyemi ◽  
Ganiyu Saheed ◽  
Oluwaseun Olurin
Keyword(s):  
Magnetic Field ◽  
Signal Amplitude ◽  
Analytic Signal ◽  
Maximum Depth ◽  
Horizontal Gradient ◽  
Aeromagnetic Data ◽  
Magnetic Gradient ◽  
Gradient Magnitude ◽  
Local Wavenumber ◽  
Intensity Magnetic Field

AbstractLocations and depths to magnetic contacts were estimated from the total intensity magnetic field using the Horizontal Gradient Magnitude (HGM), Analytic Signal Amplitude (ASA) and Local Wavenumber (LWN) methods. Aeromagnetic data from the Ibadan area, in south-western Nigeria, were analyzed to estimate depths to magnetic sources as well as source locations. The minimum/maximum depth limits of the HGM and LWN are relatively close and comparable, while shallow source depths limits are greater than expected in the ASA method when compared with the HGM and LWN functions.

scholarly journals Estimating Effectiveness of Some Methods for Detecting Edge of Potential Field Sources

2020 ◽  
Vol 36 (4) ◽  
Author(s):  
Pham Thanh Luan ◽  
Le Thi Sang ◽  
Vu Duc Minh ◽  
Ngo Thi To Nhu ◽  
Do Duc Thanh ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Tilt Angle ◽  
Northeast China ◽  
Signal Amplitude ◽  
Analytic Signal ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
North Vietnam ◽  
Gradient Amplitude

This paper presents a comparative study of effectiveness of edge detection methods such as total horizontal gradient, analytic signal amplitude, tilt angle, gradient amplitude of tilt angle, theta map, horizontal tilt angle, tilt angle of total horizontal gradient, tilt angle of analytic signal, improved theta map, and total horizontal gradient of improved tilt angle. The effectiveness of each method was estimated on synthetic magnetic data and synthetic gravity anomaly data with and without noise. The obtained results show that the tilt angle of gradient amplitude can detect all the edges more clearly and precisely. The applicability of each method is demonstrated on the aeromagnetic anomaly data from the Zhurihe region of Northeast China, and Bouguer gravity anomaly data from a region of North Vietnam. The results computed by the tilt angle of horizontal gradient were also in accord with the geologic structures of the areas.

scholarly journals Basement Classification through Enhanced Magnetic Data Reductions in parts of Ekiti State, Southwestern Nigeria

2017 ◽  
Vol 6 (1) ◽  
pp. 1
Author(s):  
Adedibu Akingboye ◽  
Abimbola Ogunyele
Keyword(s):  
Automatic Gain Control ◽  
Gain Control ◽  
High Amplitude ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Southwestern Nigeria ◽  
Basement Rocks ◽  
Low Amplitude ◽  
Data Reductions

Enhanced magnetic data reductions via the use of various forms of filters were employed for basement classification in parts of Ekiti State. The data reductions and enhancement involve: reduction to equator (RTE), regional and residual, automatic gain control (AGC), downward continuation, upward continuations (1, 2, and 3 km), analytic signal (AS) and horizontal gradient (HG) to map and delineate basement rocks and structures, while surface relief and spectral plot were used to determine depth to top of magnetic sources. The images revealed that the study area is characterized by different lithologies. The rocks evinced lineaments and faults trending NE-SW (G–G’, H–H’, J–J’, K–K’), NNE-SSW, E-W (minor) and approximately N-S, while the dykes are in NW-SE, NNW-SSW directions. The analytic signal (AS) and horizontal gradient (HG) revealed high amplitude reversed Z-like shape as migmatite rocks, differentiating them from the two flanks with low amplitude signals as schist and quartzite schist of Ijero and Aramoko and the granitic intrusive within these migmatised rocks around Ijan, Gbonyin and Ise/Otun. The shaded relief and the spectral plot showed that the total depth to top of magnetic sources ranged from 20m to 1.8km for shallower and deeper sources respectively.

scholarly journals LOCATION OF MAGNETIC CONTACTS AND DEPTH ESTIMATES FOR THE MAGNETIC SOURCES FROM THE AEROMAGNETIC DATA OF MACEDONIA AND THRACE

2004 ◽  
Vol 36 (3) ◽  
pp. 1252
Author(s):  
Α. Σταμπολίδης ◽  
Γ. Τσόκας
Keyword(s):  
Magnetic Field ◽  
Analytical Signal ◽  
Crystalline Basement ◽  
Horizontal Gradient ◽  
Aeromagnetic Data ◽  
Local Wavenumber

In this work we present the processing that applied to digitised aeromagnetic data from Macedonia and Thrace. This processing was aiming the calculation of magnetic contacts and depths of burial of magnetic sources in the region of study. Three methods were applied for these calculations: the method of horizontal gradient, the method of analytical signal and the method of local wavenumber. All methods were successful in locating the deeper magnetic sources in basins and surface sources in regions with surface outcrops of the crystalline basement. Depending on the transformation of magnetic field we use as input for the methods of the horizontal gradient and analytical signal, we could calculate the minimum and maximum depths of burial for the magnetic contacts. The locations of magnetic contacts that were calculated for every method of analysis were combined in a map in order to help in the interpretation of proposed magnetic contacts

scholarly journals High resolution airborne radiometric and magnetic studies of ilesha and its environs, southwestern Nigeria

2019 ◽  
Vol 66 (1) ◽  
pp. 51-73
Author(s):  
I. C. Okeyode ◽  
O. T. Olurin ◽  
S. A. Ganiyu ◽  
J. A. Olowofela
Keyword(s):  
Dose Rate ◽  
Extreme Values ◽  
Signal Amplitude ◽  
Geological Structure ◽  
Horizontal Gradient ◽  
Magnetic Studies ◽  
Southwestern Nigeria ◽  
Porphyritic Granite ◽  
Local Wavenumber ◽  
Apparent Susceptibility

AbstractThe study of the nature of distribution of natural radioelements in Ilesha and its environs with its geological structure has been studied using aeroradiometric data. Aeromagnetic data have also been subjected to three automated gradient techniques to delineate the sub-surface structure of the study area. From the study, it can be found that maximum values of “eU” (ppm) and “eTh” (ppm) fall within the branded gneiss, whereas the maximum value of K (%) falls within porphyritic granite regions. eTh had the highest radioactive content. The environmental dose rate of Ilesha was between 0.1817 and 3.9296 msv/yr. Although there were extreme values, but the mean dose rate was 0.522 ± 0.310 msv/yr (within acceptable safe limit of 1.0 msv/yr). eU/K, eU/eTh and eTh/K ratios were analysed for enrichment or depletion of radioisotopes. eU/eTh >1 showed uranium depletion, while eTh >2 showed eTh enrichment. The magnetic intensity values ranged from -79.41 to 140.93 nT. The horizontal gradient method (HGM) and analytic signal amplitude (ASA) revealed that depth to magnetic sources ranged from 0.478 to 4.112 km and 0.348 to 2.551 km, respectively, whereas local wavenumber (LWN) depth ranged from 0.478 to 5.48 km, which overestimated those compared using HGM and ASA functions. The apparent susceptibility ranged from -0.00325 to 0.00323 SI, showing that ferromagnetic and diamagnetic mineral ranges control apparent susceptibility in Ilesha.

Sign in / Sign up

Export Citation Format

Share Document