Vertical Magnetic Component Research Articles

MULTILEVEL GRADIENT GENERATOR FOR STUDYING THE EFFECT OF HYPOMAGNETIC FIELDS ON BIOLOGICAL OBJECTS

A multilevel generator has been developed based on a gradient magnetic field source using square Helmholtz coils, which makes it possible to create changes in the level of the magnetic field in the horizontal plane with a constant vertical magnetic component. The error in setting the generated magnetic field can reach 4 %, which is comparable to natural fluctuations of the Earth's magnetic field. The generator provides experiments with biological objects in the working area of square Helmholtz coils with a volume of at least 0.25 m3, reducing the experiment time by more than five times. The developed design options for a multilevel generator make it possible to conduct a variety of magnetobiological experiments: in a uniform and gradient magnetic field, with magnetic field inversion and transition through the zero value, in combined magnetic fields.

A Rapid Forward for Grounded Long Wire Source Transient Electromagnetic Method

Aiming at enhancing the forward and inversion efficiency of grounded long wire source TEM (Transient ElectroMagnetic method), a new rapid layered medium forward method is proposed in the paper. This forward method is based on two points, one is to approximate the vertical magnetic component in frequency domain of a grounded long wire source by the response of several circular loops, and the other is to introduce the technique of "flow through" into the digital filtering calculation of sinusoidal transformation. The result of model tests shows that the calculation efficiency of proposed method is improved greatly (dozens of times) compared with that of the conventional method.

Comparison of short-offset and long-offset grounded-wire transient electromagnetic responses based on the 3D model

In this study, a recently developed time-domain electromagnetic method called the short-offset grounded-wire transient electromagnetic (SOTEM) method, which is a near-source observation method, was adopted to obtain strong signals and great detection depths. The responses of the SOTEM and long-offset transient electromagnetic (LOTEM) methods were compared to further guide and promote the SOTEM method. Currently, the comparison between SOTEM and LOTEM methods is primarily based on one-dimensional (1D) models. However, most geological bodies are three-dimensional (3D) structures. We investigated the responses of a grounded-wire transient electromagnetic method based on 3D models using the 3D finite-difference time-domain method. In addition, the signal strengths, detection sensitivities and detection depths of the SOTEM and LOTEM methods were compared. The results revealed that the field amplitudes of Ex (electrical component parallel to the transmitting source) and ∂By/∂t (magnetic component perpendicular to the transmitting source horizontally) were higher at the short offsets than at the long offsets. For the ∂Bx/∂t (magnetic component parallel to the transmitting source) and the vertical magnetic component ∂Bz/∂t, at initial times, the responses received would be stronger when closer to the transmitting source, whereas at later times, the responses would be stronger when farther from the source. Ex detection sensitivity increased with an increase in the offset at initial times, and increased with a decrease in the offset at later times. The detection sensitivities of the three magnetic field components at short offsets were higher than those at long offsets. The ∂By/∂t effective detection depth was the greatest. Generally, the effective detection depths of the three magnetic field components increased with decreasing offset. The range of the ratio of the horizontal distance, r, between the transmitting source and the target body to the effective detection depth H was 0.5-1.1.

A localization method for subsea pipeline based on active magnetization

Accurate location of subsea pipelines is a prerequisite for real-time tracking and detailed inspections by underwater robots. The magnetic anomalies generated by ferromagnetic pipelines can be used to locate both exposed and buried pipelines. However, due to the low signal ratio and model inconsistencies under weak and variable ambient magnetization, there is currently no intuitive and reliable pipeline detection method for pipeline tracking. This paper proposes a method capable of immediately and accurately locating pipelines via active magnetization and vertical magnetic measurements. Finite element simulations show that a magnet array can significantly enhance the magnetic anomaly, and that the vertical magnetic component alone can accurately indicate the pipeline’s position, avoiding the inconvenience of magnetic three-component alignment in the field. It is experimentally demonstrated that the magnetic detection signal-to-noise ratio can be significantly increased by 5 dB–20 dB for a Φ219 mm steel pipe using the magnet array, and the maximum lateral positioning error is 0.03 m and much smaller than that without the magnet array.

A Hybrid Calibration Method for a Three-Axis Magnetometer in Limited-Range Attitudes

The calibration of a three-axis magnetometer plays a vital role in its wide practical applications. Most previous calibration methods are based on the invariance of the magnitude of the magnetic field vector. However, this kind of method degrades seriously when the training data are collected at limited-range attitudes and are much of relevance. A new calibration model of magnetometer based on the combination of magnitudes of horizontal and vertical magnetic components is proposed. The numerical simulations demonstrate the proposed method can exactly estimate the error parameters both in the case of small and large-range rotation angle. The result of the physical experiment is consistent with simulations, showing the method in this paper has a better calibration performance than previous methods when the range of attitude angle of the magnetometer is limited.

Estimating Locations and Moments of Multiple Dipole-Like Magnetic Sources From Magnetic Gradient Tensor Data Using Differential Evolution

In this article, we present a new method for the detection and localization of multiple dipole-like magnetic sources using magnetic gradient tensor data. We use the tilt angle that is the ratio of the vertical magnetic component to the horizontal field to determine the number of the magnetic sources and use the rotational-invariant normalized source strength (NSS) to estimate approximate horizontal coordinates of the magnetic sources. The differential evolution (DE) algorithm is used to estimate the locations and moments of the magnetic sources. Three synthetic examples, with and without random noise, are designed to validate the proposed method. The locations and magnetic moments of the magnetic sources can be well determined. The proposed method has also been applied to a field test with multiple magnetic sources and the result shows that the location of the magnetic source can be estimated well.

Direct Comparison of the Tsunami‐Generated Magnetic Field With Sea Level Change for the 2009 Samoa and 2010 Chile Tsunamis

AbstractThe motion of conductive seawater by tsunamis can generate magnetic fields in the presence of the background geomagnetic main field. Previous studies found that, using the tsunami‐generated seafloor magnetic field, it is possible to predict the propagation direction and wave height prior to the actual arrivals of tsunamis. This study correlates the tsunami magnetic field and the tsunami sea level change using observed data and three‐dimensional simulations of the 2009 Samoa and 2010 Chile tsunamis. Our direct comparison of the tsunami observed magnetic field and tsunami sea level change illustrate that the vertical tsunami magnetic component, , arrived earlier than the sea level change. The “initial rise” signal in the observed horizontal tsunami magnetic component, , which was arrived even earlier than also is found by combing the observation with the three‐dimensional simulations. We further examine the precision of conversion of the tsunami magnetic field to the sea level change and find that the magnetic field derived tsunami sea levels are as precise as those obtained from differential pressure gauge data. However, our simulation shows that existing tsunami source models are incompatible with our tsunami magnetic data. Therefore, it is necessary to include magnetic field derived tsunami sea level changes to improve those source models.

Average Ionospheric Middle and Low Latitudes Nighttime Zonal Currents Deduced From CHAMP

AbstractBy utilizing magnetic field measurements collected by CHAMP during the years 2001–2009, average characteristics of nighttime ionospheric zonal currents at middle and low latitudes are investigated. We provide for the first time the detailed dependencies of these currents on location, local time, season, and the level of solar activity. The main results obtained are (1) the nighttime zonal ionospheric currents at F‐region altitude, derived from the vertical magnetic component, exhibit on average height‐integrated current densities up to 10 mA/m. The amplitude varies quasi‐linearly with F10.7 flux level. (2) During equinoxes symmetric current systems at F‐region altitude are found in the two hemispheres. After sunset, eastward currents dominate at low latitudes, fading away toward midnight. After midnight regions of eastward currents are observed at midlatitude. During solstice seasons, eastward currents are enhanced in the summer hemisphere; westward currents are stronger in local winter. (3) Longitudinal variations of F‐region currents show clear wave‐1 patterns. This is related to the effect of the stationary planetary wave‐1 and the diurnal nonmigrating tide, D0. This dominant tidal signal, enhancing eastward currents over the Pacific region, appears at middle and low latitudes and during all seasons. (4) At the magnetic equator, signs of the equatorial electrojet (EEJ) are evident after 02:30 MLT. Intensity of westward currents in the narrow band increases toward sunrise. Longitudinal variations of the EEJ show a similar wave‐1 pattern as F‐region currents. Here the westward current density is enhanced over Africa/India. The EEJ wave‐1 modulation is strongest around June solstice.

Numerical simulations to explain the coseismic electromagnetic signals: a case study for a M5.4 aftershock of the 2016 Kumamoto earthquake

Coseismic electromagnetic (EM) signals that appear from the P arrival were observed in a volcanic area during the 2016 Kumamoto earthquake. In this study, we conduct numerical simulations to explain the coseismic EM signals observed for a M5.4 aftershock of the earthquake. Initially, we adopt a water-saturated half-space model, and its simulation result for a receiver with a depth of 0.1 m suggests that the magnetic signals do not show up at the arrivals of P, refracted SV–P and Rayleigh waves because the evanescent EM waves just counterbalance the localized magnetic signals that accompany P, refracted SV–P and Rayleigh waves. Then, we conduct numerical simulations on a seven-layer half-space model in which the second layer corresponds to an aquifer analogy and the six other layers refer to air-saturated porous media. When only the electrokinetic effect is considered, the simulated coseismic magnetic signals still appear from the S arrival. The combination of electrokinetic effect and surface-charge assumption is also tested. We find that signals before the S arrival are missing on the transverse seismic, transverse electric, radial magnetic and vertical magnetic components, although the situation on horizontal magnetic components is improved to an extent. Then, we introduce an artificial scattering effect into our numerical simulations given that the scattering effect should exist in the volcanic area. New numerical result shows good agreement with the observation result on the signal appearance time. Hence, the combination of electrokinetic and scattering effects is a plausible explanation of coseismic EM signals. Further investigations indicate that coseismic electric and/or magnetic signals are more sensitive to the scattering effect and the aquifer thickness than seismic signals.

On the exploration of a marine aquifer offshore Israel by long‐offset transient electromagnetics

ABSTRACTThe existence of aquifers extending from land beneath the sea floor up to a distance of several kilometres has been observed and examined all over the world. The coastal aquifer of Israel is a heavily used groundwater reservoir which has to be constantly monitored to ensure the drinking water supply. Former land‐based electromagnetic measurements show that it is, in several places, blocked to seawater intrusion and is consequently a candidate for submarine extension. Multicomponent long‐offset transient electromagnetic measurements were carried out offshore on the coast of Israel. We deployed a 400‐m‐long grounded dipole as transmitter and several electric and magnetic receivers on the sea floor up to a distance of 4.8 km from the coast. Altogether, we deployed 8 transmitter positions and received data sets at 14 receiver stations onshore and offshore, with offsets of mostly 400 and 800 m. In this paper, we present the survey and 1D Occam and Marquardt inversions of the offshore horizontal electric components in the broadside and inline configuration. In addition, the vertical magnetic component in the broadside position is also considered. Only single inversions, both single offset and single component, were used to detect the aquifer under sea sediments. We prove the submarine existence of the Israeli coastal aquifer up to a distance to the coast of approximately 3.2 to 3.6 km using all measured long‐offset transient electromagnetic components. In addition, we present modelling studies with synthetic data derived from a subsurface model adjusted to our survey area with very shallow water from 10 to 50 m. As part of the planning before the survey, a parameter study of the expected subsurface, the examination of the airwave phenomenon and the justification for our 1D inversion strategy are shown. More detailed eigen parameter analyses are added to explain the measured data.

Regularity criteria for the two-and-half-dimensional magnetic B\xe9nard system with partial dissipation, magnetic diffusion, and thermal diffusivity

This paper concentrates on the global regularity of classical solution to the 2frac{1}{2}D magnetic Bénard system with partial dissipation, magnetic diffusion, and thermal diffusivity (i.e., horizontal dissipation, horizontal magnetic diffusion, and horizontal thermal diffusivity; vertical dissipation, vertical magnetic diffusion, and vertical thermal diffusivity). For the 2frac{1}{2}D magnetic Bénard system with full dissipation, magnetic diffusion, and thermal diffusivity, the global existence and uniqueness can be obtained by the standard energy method. However, can the classical solution for the 2frac{1}{2}D incompressible magnetic Bénard system still keep its global regularity when losing some partial dissipation, magnetic diffusion, and thermal diffusivity terms? We will give a rigorous proof to the global regularity for the 2frac{1}{2}D magnetic Bénard system with horizontal and vertical dissipation, magnetic diffusion, and thermal diffusivity respectively in this paper. Furthermore, we also show that any possible finite time blow-up can be controlled by the L^{infty }-norm of the vertical velocity and magnetic components, not include the temperature component (see Theorems 1.1 and 1.2). The results extend the recent work by Cheng and Du (J. Math. Fluid Mech. 17:769–797, 2015), and generalize the recent works by Regmi (Math. Methods Appl. Sci. 40:1497–1504, 2017), and Ma and Zhang (Bound. Value Probl. 2018:79, 2018).

The device with fluxgate sensor for joint tracking

The possibility to evaluate electron beam deflection from joint by magnetic field strength of the current flowing through the welded part of joint is studied. The differential flux gate is utilized as a sensor of electron beam and joint displacement. The concept of the proposed way of electron beam position control relatively to joint is that welding current is divided into two components. Value of beam deflection is defined due to value and direction of vertical magnetic field strength component. At the same time magnetic field strength over welded part of joint is measured.

An analytical algorithm for 3D magnetic field mapping of a watt balance magnet

A yoke-based permanent magnet, which has been employed in many watt balances at national metrology institutes, is supposed to generate strong and uniform magnetic field in an air gap in the radial direction. However, in reality the fringe effect due to the finite height of the air gap will introduce an undesired vertical magnetic component to the air gap, which should either be measured or modeled towards some optimizations of the watt balance. A recent publication, i.e. Li et al (2015 Metrologia 52 445), presented a full field mapping method, which in theory will supply useful information for profile characterization and misalignment analysis. This article is an additional material of Li et al (2015 Metrologia 52 445), which develops a different analytical algorithm to represent the 3D magnetic field of a watt balance magnet based on only one measurement for the radial magnetic flux density along the vertical direction, Br(z). The new algorithm is based on the electromagnetic nature of the magnet, which has a much better accuracy.

Numerical simulations of turbulent ionized gas flows in the circumsolar protoplanetary disk

An axisymmetric protoplanetary disk model that takes into account the interaction of turbulent gas flows with the magnetic field is considered. A closed system of equations of homogeneous compressible magnetohydrodynamics in the regime of developed turbulence in the gravitational and magnetic fields of a star has been constructed. Apart from the traditional probability-theoretical averaging of the MHD equations, the weighted Favre averaging is used. The approach by A.V. Kolesnichenko and M.Ya. Marov to modeling the turbulent transport coefficients in a weakly ionized disk has been implemented. It allows the inverse effects of the generated magnetic field on a turbulent gas flow and the dissipation of turbulence through kinematic and magnetic viscosities to be taken into account. A parallel code for numerically solving the system of averaged MHD equations has been developed. The averaged gas density and velocity distributions as well as the configuration of the disk’s intrinsic magnetic field at a distance of 1 AU from the star have been obtained through numerical simulations. The assumption that the vertical (parallel to the disk’s rotation axis) magnetic induction component changes much more profoundly in height than in radius and, hence, gives grounds to take into account its gradient in the model of the turbulent kinematic viscosity coefficient has been confirmed.

Anomalously strong vertical magnetic fields from distant ELF/VLF sources

AbstractThere are many sources of very low frequency (VLF—3–30 kHz) and extremely low frequency (ELF—3–3000 Hz) radiation in the Earth‐ionosphere waveguide (e.g., lightning and ELF/VLF communication transmitters). At distances of thousands of kilometers from these sources, the vertical component of the ELF/VLF AC magnetic fields is expected to be very weak and several orders of magnitude lower than the horizontal magnetic components. However, measurements in Israel show a relatively strong vertical magnetic component in both the ELF and VLF bands, at the same order of magnitude as the horizontal components. Our measurements suggest that the real Earth‐ionosphere waveguide might often be very different from the theoretical waveguide used in model calculations. In addition, our results imply that using only the horizontal components for direction finding or the absolute magnetic field strength may result in errors, since often a significant fraction of the magnetic field energy hides in the vertical component.

Magnetic transfer function entropy and the 2009 <i>M</i><sub>w</sub> = 6.3 L'Aquila earthquake (Central Italy)

Abstract. With the aim of obtaining a deeper knowledge of the physical phenomena associated with the 2009 L'Aquila (Central Italy) seismic sequence, culminating with a Mw = 6.3 earthquake on 6 April 2009, and possibly of identifying some kind of earthquake-related magnetic or geoelectric anomaly, we analyse the geomagnetic field components measured at the magnetic observatory of L'Aquila and their variations in time. In particular, trends of magnetic transfer functions in the years 2006–2010 are inspected. They are calculated from the horizontal to vertical magnetic component ratio in the frequency domain, and are very sensitive to deep and lateral geoelectric characteristics of the measurement site. Entropy analysis, carried out from the transfer functions with the so called transfer function entropy, points out clear temporal burst regimes of a few distinct harmonics preceding the main shock of the seismic sequence. A possible explanation is that they could be related to deep fluid migrations and/or to variations in the micro-/meso-fracturing that affected significantly the conductivity (ordered/disordered) distribution in a large lithospheric volume under the seismogenic layer below L'Aquila area. This interpretation is also supported by the analysis of hypocentres depths before the main shock occurrence.

Variations in the schumann resonance polarization ellipse in the horizontal and vertical planes according to observations at the Barentsburg and Lovozero observatories

The diurnal variations in the amplitude and parameters of polarization ellipses of the first Schumann resonance according to three magnetic field components, observed on December 1–10, 2007, at the Barentsburg and Lovozero observatories, have been studied. Ellipses have been constructed in the (H, D) and (H, Z) planes. The value of the minor axis, inclination of the major axis, ellipticity, and the rotation direction have been estimated. The vertical magnetic component of the Schumann resonance is three to four times as small as the horizontal component. The difference in the diurnal variations in the ellipse parameters between both observatories has been found. The effect can be caused by a difference in the Earth’s conductivity in the vicinity of the observatories and by conductivity anisotropy. The major axis inclination and ellipticity have semidiurnal components. The polarization vector mostly rotates from D to H in the horizontal plane and from Z to H in the vertical plane at both stations.

Magnetic Base Station Deceptions, a magnetovariational analysis along the Ligurian Sea coast, Italy

Reliability of high resolution airborne and shipborne magnetic surveys depends on accurate removal of temporal variations from the recorded total magnetic field intensity data. At mid latitudes, one or a few base stations are typ- ically located within or near the survey area and are used to monitor and remove time dependent variations. These are usually assumed to be of external origin and uniform throughout the survey area. Here we investigate the influence on the magnetic base station correction of the time varying magnetic field variations generated by internal telluric currents flowing in anomalous regional 2D/3D conductivity structures. The study is based on the statistical analysis of a data set collected by four magnetovariational stations installed in northwestern Italy. The variometer sta- tions were evenly placed with a spacing of about 60 km along a profile roughly parallel to the coastline. They record- ed the geomagnetic field from the beginning to the end of April 2005, with a sampling rate of 0.33 Hz. Cross-corre- lation and coherence analysis applied to a subset of 125 five hours long magnetic events indicates that, for periods longer than 400 s, there is an high correlation between the horizontal magnetic field components at the different sta- tions. This indicates spatial uniformity of the source field and of the induced currents in the 1D Earth. Additionally, the pattern of the induction arrows, estimated from single site transfer functions, reveals a clear electromagnetic sig- nature of the Sestri-Voltaggio line, interpreted as a major regional tectonic boundary. Induced telluric currents flow- ing through this 2D/3D electrical conductivity discontinuity affect mainly the vertical magnetic component at the closer locations. By comparing this component at near (32 km) and far (70 km) stations, we have found that the mean value of the power spectra ratio, due to the electromagnetic induced field, is about 1.8 in the frequency band rang- ing from 2.5 ×10 −3 to 5.5 ×10 −5 Hz. This energy, folded in the spatial domain of an hypothetical survey in this region produces unwanted noise in the dataset. Considering a fifth of nyquist frequency the optimal tie-line spacing to as- sure complete noise removal would be 1 km and 15 km for a rover speed of 6 knots (marine magnetic survey) and 100 knots (aeromagnetic survey) respectively. Similar power spectra analysis can be applied elsewhere to optimise tie-line spacing for levelling and filtering parameters utlilised for microlevelling.

The seasonal behavior of the B z daily variations according to the monitoring at the Bishkek geodynamic site (1993–1995)

The algorithm for monitoring the magnetotelluric field has been briefly described, and the experimental data, obtained at the Bishkek geodynamic site, have been analyzed. The regularities in the seasonal behavior of the variations in the field vertical magnetic component have been revealed.

An electromagnetic sounding experiment in Germany using the vertical gradient of geomagnetic variations observed in a deep borehole

SUMMARY We have recorded for 13 d, geomagnetic variations simultaneously on the Earth's surface and in a borehole at 832 m depth straight below, with a sampling rate of 1 Hz. In addition, geoelectric variations were observed at the same site near Bad Konigshofen in Frankonia, Germany. The penetrated moderately conductive Triassic sediments lie above highly resistive Permian deposits. A presumably crystalline basement begins at 1500–1900 m depth. The purpose of the experiment is to determine the skin effect of geomagnetic variations and to derive from it the equivalent to the magnetotelluric (MT) surface impedance, using the vertical gradient (VG) method of electromagnetic (EM) sounding. In this way, we were able to reproduce all four elements of the MT impedance tensor, except for an unexplained but consistent downward shift of VG phases against MT phases by roughly 15° for the two off-diagonal elements. Hence, our tensor evaluation goes beyond the common practice, to express the skin effect by a single VG transfer function in response to a layered structure. The otherwise good agreement of VG and MT results implies that at our test site, the MT impedance tensor is largely distortion-free and that, for example, its pronounced anisotropy should be regarded as a genuine characteristic of the EM response for a laterally non-uniform or possibly anisotropic deep structure. The drilling site lies within the range of a widespread induction anomaly. We have observed the resulting variations of the vertical magnetic component at the surface and in the borehole and found them to be identical. The thus established absence of a skin effect for the vertical component allows us to treat the sedimentary layer down to the depth of the borehole instrument as a thin sheet, and the pertinent thin-sheet approximation for EM induction forms the basis of our analysis. We have derived the required estimate of conductance from the skin effect of horizontal components, noting that this estimate has to be real valued and the same for all frequencies. We were unable, however, to verify the resulting value of 76 S with independent geoelectric direct current (DC) measurements in the borehole and at the Earth's surface. A model study shows that the thin-sheet conductance, which is relevant for the skin effect, may be substantially higher than the depth-integrated conductivity from DC data. Robust estimates of transfer functions were derived for 20 frequencies from 5.625 to 0.007 cpm, which corresponds to periods from 10 to 10000 s. Squared skin effect coherencies are above 0.9 for periods longer than 20 s and thereby comparable to MT coherencies.