scholarly journals Enhancing the quality of interpretation magnetic data at low latitudes

2017 ◽  
Vol 1 (T4) ◽  
pp. 105-114
Author(s):  
Hai Hong Nguyen ◽  
Nhan Thanh Nhan ◽  
Liet Van Dang ◽  
Thu Ngoc Nguyen
Keyword(s):  
Magnetic Anomaly ◽  
Hilbert Transform ◽  
Amplitude Spectrum ◽  
Data Interpretation ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Low Latitudes ◽  
Reduction To The Pole ◽  
Signal Method

Magnetic anomalies are antisymmetrical and often skewed to the location of the sources, because both of the magnetization and ambient field are not directed vertically, so it’s difficult to interpret. For reducing the magnetic anomaly to a symmetrical one – this located on the source of the anomaly – people often use the reduction to the pole (RTP) where the magnetization and ambient field are both directed vertically. However, at low latitudes (an absolute inclination less than 16o30’), the amplitude spectrum of the RTP’s operator was amplified at higher frequencies (short wavelengths) can form a narrow pie-shaped; so it produces artifacts elongated along the direction of the magnetic declination. Therefore, many methods of RTP at low latitudes are given to solve this problem, but most of them are not efficiency. In this paper, we performed enhancing the quality of interpretation of magnetic data at low latitudes by some RTP methods for magnetic data at low latitudes and the analytic signal method using gradient operator and Hilbert transform. This method is applied to a model and to a real magnetic anomaly to find out the best method. Then this method was applied to enhance the quality of magnetic data interpretation in the Southern Vietnam. The result showed that the analytic signal method using Hilbert transform allowed enhancing the quality of interpretatio of magnetic data n at low latitudes is the best.

CEPSTRUM ALIASING AND THE CALCULATION OF THE HILBERT TRANSFORM

Geophysics ◽  
1974 ◽  
Vol 39 (4) ◽  
pp. 543-544 ◽  
Author(s):  
Paul L. Stoffa ◽  
Peter Buhl ◽  
George M. Bryan
Keyword(s):  
Hilbert Transform ◽  
Phase Function ◽  
Amplitude Spectrum ◽  
Magnetic Data ◽  
Minimum Phase ◽  
Original Function ◽  
Cepstrum Analysis ◽  
Complex Cepstrum ◽  
The Hilbert Transform ◽  
Special Case

Schafer (1969) has pointed out that the Hilbert transform approach used in computing the minimum‐phase spectrum of a given amplitude spectrum corresponds to a special case of complex‐cepstrum analysis in which the phase information of the original function is ignored. The resulting complex cepstrum is an even function. Since a minimum‐phase function has no complex‐cepstrum contributions for T<0, its even part must exactly cancel the odd part for T<0. Thus, by setting all complex‐cepstrum contributions for T<0 equal to zero and doubling all contributions for T>0, we obtain the complex cepstrum of the minimum‐phase function corresponding to the original function. However, the DFT-calculated complex cepstrum is an aliased function (Stoffa et al., 1974). Thus some negative periods will appear at positive locations and vice versa. Appending the original function with zeros will reduce the aliasing. Shuey (1972), in computing the Hilbert transform for magnetic data, indicates that the computation breaks down near the end of the profile, or at long cepstrum periods. This is precisely the point in the even cepstrum where aliasing will have its greatest effect.

scholarly journals Exploration of Iron Sand at The Eastern Coast Area of Binangun in Cilacap Regency Using Magnetic Survey

2017 ◽  
Vol 7 (2) ◽  
pp. 71 ◽  
Author(s):  
Sehah Allasimy ◽  
Sukmaji Anom Raharjo ◽  
Iska Andriyanto
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Anomaly ◽  
Data Interpretation ◽  
Research Area ◽  
Eastern Coast ◽  
Magnetic Data ◽  
Magnetic Survey ◽  
Magnetic Field Data ◽  
Geological Information ◽  
Geoelectric Data

<p class="AbstractText">Exploration of the spread of iron sand on the eastern coastal of Binangun District in Cilacap Regency has been conducted using the magnetic surveys. The magnetic data acquisition was conducted in April 2017. The total magnetic field data obtained is processed, so that can be obtained the local magnetic anomaly data. The modeling of the local magnetic anomaly data is performed on the trajectory of AB that extending from the position point of 109,274698° E and 7.686620° S to 109.2296195° E and 7.689099° S so that obtained various model of the subsurface anomalous objects. Interpretation on the subsurface anomalous objects is done to estimate the types of rocks and their formations based on the magnetic susceptibility value of each object which supported by the geological information of the research area. Based on the interpretation results to be obtained two layers of subsurface rocks that can be estimated as the iron sand that coexists with silt dan clay derived from the alluvium formation. The first rock has a length of 1238.2 meters, a depth of 1.709 – 20.513 meters, and a magnetic susceptibility value of 0.0183 cgs unit. The second rock has a length of 643.055 meters, a depth of 16.524 – 34.188 meters, and a magnetic susceptibility value of 0.0174 cgs unit. The results of this research are also supported by the results of geoelectric data interpretation, where the iron sand that coexists with silt and clay is found at a depth of 9.42 – 19.48 meters with a resistivity value of 52.99 Ωm at Geo-1 point; and a depth of 10.56 – 22.20 meters with resistivity value of 49,03 Ωm at Geo-2 point. Based on the results of of this research, the eastern coastal area of Binangun District is estimated to contain potentially iron ore and economically is a prospect for exploitation.</p>

scholarly journals Analytic Signal and Euler Depth Interpretation of Magnetic Anomalies: Applicability to the Beatrice Greenstone Belt

2015 ◽  
Vol 7 (4) ◽  
pp. 108
Author(s):  
Thabisani Ndlovu. ◽  
Mashingaidze R. T. ◽  
Mpofu P.
Keyword(s):  
Regional Scale ◽  
Data Interpretation ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Body Location ◽  
Geological Map ◽  
Ground Magnetic ◽  
Depth Relationship ◽  
Two Parameters ◽  
Good Agreement

We apply the Analytic Signal and Euler depth filtering techniques on magnetic data to identify a magnetic causative body location-depth relationship, two parameters of importance in both geophysical exploration and ore body modelling. We identify a dipping magnetic contact from the interpreted Euler depth anomalies, showing a good agreement with both the Total Field Magnetic (TFM) map and the Analytic Signal (AS) map. The Euler depth anomalies correlate well with the locations and edges of shallow causative bodies. The deeper Euler interpreted sources explain the magnetic high on the regional aeromagnetic map which is coincident with neither geological contacts nor the more recent dolerite intrusions. This suggests that the magnetic highs on the regional aeromagnetic map are due to deep seated sources, otherwise invisible on the regional geological map. The results show the usefulness and relevancy of these two filters not only in interpreting routine TFM data from the study area, but up to a regional scale. While the aeromagnetic data shows that the magnetisation pattern is predominantly divorced from the geological map, the ground magnetic data interpretation points to a more recent magnetisation of the belt, enabling conclusions to be drawn about the geological history and structural geology otherwise not evident on the geological map.

Reduction to the pole at low latitudes by Wiener filtering

Geophysics ◽  
1989 ◽  
Vol 54 (12) ◽  
pp. 1607-1613 ◽  
Author(s):  
R. O. Hansen ◽  
R. S. Pawlowski
Keyword(s):  
Frequency Domain ◽  
Synthetic Data ◽  
Wiener Filtering ◽  
Magnetic Data ◽  
Noise Power ◽  
Low Latitude ◽  
High Quality ◽  
Computational Load ◽  
Low Latitudes ◽  
Reduction To The Pole

Using simple estimates of the signal and noise power from gridded magnetic data, we design regulated frequency‐domain operators for reduction to the pole at low magnetic latitudes. These operators suppress the artifacts along the direction of the magnetic declination associated with the conventional reduction‐to‐the‐pole procedure, with negligible increase in computational load. The new procedure is applied to produce high‐quality reductions to the pole for noisy low‐latitude synthetic data and for magnetic data from the Dixon Seamount.

Using the analytic signal amplitude to determine the location and depth of thin dikes from magnetic data

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. J1-J6 ◽  
Author(s):  
Gordon R. J. Cooper
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomaly ◽  
Magnetization Vector ◽  
Signal Amplitude ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Local Minima ◽  
First Order ◽  
Higher Order Derivative ◽  
The Magnetic Field

A semiautomatic method to determine the location and depth of thin dykes is introduced. The ratio of analytic signal amplitudes of orders 0 and 1 of the magnetic anomaly from a thin dike was used to give the distance [Formula: see text] to the dike. Local minima of [Formula: see text] gave the depth to the dike, and the position of these minima gave its horizontal location. Because in the method we used just the magnetic field and its first-order derivatives, it was less sensitive to noise than were higher order derivative-based methods. Once the position of the dike has been determined, then its dip and susceptibility-thickness product can be calculated from the analytic signal amplitude, providing that the magnetization vector is known.

Identifying remanent magnetization effects in magnetic data

Geophysics ◽  
1993 ◽  
Vol 58 (5) ◽  
pp. 653-659 ◽  
Author(s):  
Walter R. Roest ◽  
Mark Pilkington
Keyword(s):  
Magnetic Anomaly ◽  
Remanent Magnetization ◽  
Close Agreement ◽  
Magnetic Anomalies ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Impact Structure ◽  
Magnetization Direction ◽  
Additional Constraints

Remanent magnetization can have a significant influence on the shape of magnetic anomalies in areas that are generally characterized by induced magnetization. Since modeling of magnetic anomalies is nonunique, additional constraints on the direction of magnetization are useful. A method is proposed here to study the possible contribution of remanent magnetization to a particular anomaly, by comparing two functions that are calculated directly from the observations: (1) the amplitude of the analytic signal, and (2) the horizontal gradient of pseudogravity. From the amplitude and relative position of maxima in these derived quantities, we infer the deviation of the magnetization direction from that of the ambient field. The approach is applied to the magnetic anomaly in the center of the Manicouagan impact structure (Canada). Our results, based only on the magnetic anomaly observations, are in close agreement with constraints on the direction of remanent magnetization from rock samples.

Archaeological Interpretation of Marine Magnetic Data

2012 ◽  
Author(s):  
Robert Gearhart
Keyword(s):  
Remote Sensing ◽  
Magnetic Anomaly ◽  
Remote Sensing Data ◽  
Data Interpretation ◽  
Magnetic Data ◽  
Magnetic Interpretation ◽  
Sensing Data ◽  
The Past ◽  
Archaeological Interpretation ◽  
Historic Significance

Interpreting remote sensing data is one of the most important tasks of archaeologists working in submerged environments. Researchers rely on remote-sensing technologies to aid their search for historic shipwrecks of interest. Magnetometers are essential for detection of buried shipwrecks. The main goal of magnetic interpretation has been to distinguish shipwrecks from debris, usually resulting in an archaeological assessment of each anomaly concerning its potential for historic significance. The past two decades have seen improvement in archaeologists' abilities to detect shipwreck anomalies. This article provides a basic, nonmathematical summary of magnetism relevant to archaeological interpretation and the evolving perceptions of shipwreck anomalies. The basis for assessing magnetic anomaly significance must be firmly rooted in empiricism in order to improve the objectivity of data interpretation.

APPLICATION OF HILBERT TRANSFORMS TO MAGNETIC PROFILES

Geophysics ◽  
1972 ◽  
Vol 37 (6) ◽  
pp. 1043-1045 ◽  
Author(s):  
Ralph T. Shuey
Keyword(s):  
Linear Combination ◽  
Hilbert Transform ◽  
Magnetic Data ◽  
Two Dimensional ◽  
Total Field ◽  
Hilbert Transforms ◽  
Vertical Field ◽  
Reduction To The Pole

Three related operations commonly performed on total‐field magnetic data are 1) conversion to vertical‐field anomaly, 2) reduction to the pole, and 3) computation of pseudogravimetric anomalies. This note shows that for profile or flight line data for which the source can be assumed to be two‐dimensional, all these operations amount to linear combination of the profile with its Hilbert transform.

Model of multicomponent narrow-band periodical non-stationary random signal

2020 ◽  
Vol 2020 (48) ◽  
pp. 17-24
Author(s):  
I.M. Javorskyj ◽  
◽  
R.M. Yuzefovych ◽  
P.R. Kurapov ◽  
◽  
...  
Keyword(s):  
Time Series ◽  
Real Time ◽  
Hilbert Transform ◽  
Spectral Properties ◽  
Narrow Band ◽  
Analytic Signal ◽  
Random Signal ◽  
Hilbert Transformation ◽  
The Hilbert Transform

The correlation and spectral properties of a multicomponent narrowband periodical non-stationary random signal (PNRS) and its Hilbert transformation are considered. It is shown that multicomponent narrowband PNRS differ from the monocomponent signal. This difference is caused by correlation of the quadratures for the different carrier harmonics. Such features of the analytic signal must be taken into account when we use the Hilbert transform for the analysis of real time series.

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