Fluxgate Magnetometer Research Articles

PERTURBAÇÕES NO CAMPO GEOMAGNÉTICO CAUSADAS PELO TERREMOTO E PELO TSUNAMI DE MAULE, CHILE (2010)

Este estudo foca na análise das perturbações do campo geomagnético que estão relacionadas com o terremoto, e consequente tsunami, que ocorreram em 27 de fevereiro de 2010 em Maule, no Chile. O objetivo deste artigo é contribuir para uma melhor compreensão dos processos físicos envolvidos nos acoplamentos Tsunami-Atmosfera-Ionosfera (TAI) e Litosfera-Atmosfera-Ionosfera (LAI). Para isto, foram utilizados registros de magnetômetros fluxgate medidos em superfície fornecidos pelo projeto LISN (do inglês Low Latitude Ionospheric Sensor Network). A metodologia de filtragem do sinal por remoção da tendência relacionada à influência solar (linha de base Sq, do inglês Solar quiet) considerando os cinco dias geomagneticamente mais calmos foi aplicada. Os resultados mostraram distúrbios geomagnéticos, em ambas componentes H e Z, nos dados filtrados que ocorreram quase instantaneamente ou com atraso de até 100 minutos após a chegada do tsunami. Estes distúrbios são atribuídos aos mecanismos oceânico e ionosférico. Estudos como esse são importantes para uma futura condição de previsão e alerta de desastres dessa natureza.

Partition Beetles Antennae Search Algorithm for Magnetic Sensor Calibration Optimization

As vector sensors, such as the fluxgate magnetometer, are more and more widely used in magnetic anomaly signal detection and location, researchers find that the error of sensors has become an essential obstacle in the application. To solve this problem, we established a calibration model with three kinds of error. A new optimization algorithm called Partition Beetles Antennae Search is provided to solve the model parameters. Simulation results show that the new algorithm can consider both accuracy and computational complexity. Besides, we set up a single three-axis fluxgate sensor experimental platform for sensor calibration and conducted related experiments. The results further prove the effectiveness and practicability of the method. The work of this article suggests an effective way to calibrate three-axis magnetometers.

Thermoelastic Response of the Juno Spacecraft's Solar Array/Magnetometer Boom and Its Applicability to Improved Magnetic Field Investigation.

Juno was inserted into a polar orbit about Jupiter on 4 July 2016. Juno's magnetic field investigation acquires vector measurements of the Jovian magnetic field using a pair of a triaxial Fluxgate Magnetometers (FGMs) colocated with four attitude‐sensing star cameras on an optical bench. The optical bench is placed on a boom at the outer extremity of one of Juno's three solar arrays. The Magnetic Field investigation (MAG) uses measurements of the optical bench inertial attitude provided by the micro‐Advanced Stellar Compass (μASC) to render accurate vector measurements of the planetary magnetic field. During periJoves, orientation of the MAG Optical Benches (MOB) is determined using the spacecraft (SC) attitude combined with transformations between SC and MOB coordinate frames. Substantial prelaunch effort was expended to maximize the thermomechanical stability of the Juno solar arrays and MAG boom. Nevertheless, the Juno flight experience demonstrates that the transformation between SC and MAG reference frames varies significantly in response to spacecraft thermal excursions associated with large attitude maneuvers and proximate encounters with Jupiter. This response is monitored by comparing attitudes provided by the MAG investigation's four Camera Head Units (CHUs) with those provided by the Stellar Reference Unit (SRU). These systematic variations in relative orientation are thought to be caused by the thermoelastic flexure of the Juno solar array in response to temperature excursions associated with maneuvers and heating during close passages of Jupiter. In this paper, we investigate these thermal effects and propose a model for compensation of the MAG boom flexure.

The Chinese Mars ROVER Fluxgate Magnetometers

The Mars Rover Magnetometers (RoMAG) will implement the first mobile magnetic field measurements on the surface of Mars. Two identical tri-axial fluxgate magnetometer sensors are mounted at the top and bottom of the mast of rover, respectively. The technology of Helmholtz compensation coil probe and digital closed-loop feedback circuit is utilized to realize high precision measurement. Each magnetometer measures the vector magnetic field with a resolution of 0.01 nT in the range of $\pm65000~\text{nT}$ . The sample rate is up to 32 Hz and the noise is $0.01~\text{nT}/\surd\text{Hz}$ @1 Hz. A rover magnetic compensation procedure was conducted to remove the most important magnetic disturbances. Mobile magnetic field measurements on the Martian surface would obtain fine-scale crust field and provide information about its remnant magnetization and any possible intrinsic magnetic field. It would help us to further understand Martian internal structure, coupling processes of solar wind-magnetosphere-ionosphere.

DESMEX: A novel system development for semi-airborne electromagnetic exploration

There is a clear demand to increase detection depths in the context of raw material exploration programs. Semi-airborne electromagnetic (semi-AEM) methods can address these demands by combining the advantages of powerful transmitters deployed on the ground with efficient helicopter-borne mapping of the magnetic field response in the air. The penetration depth can exceed those of classic airborne EM systems because low frequencies and large transmitter-receiver offsets can be realized in practice. A novel system has been developed that combines high-moment horizontal electric bipole transmitters on the ground with low-noise three-axis induction coil magnetometers, a three-axis fluxgate magnetometer, and a laser gyro inertial measurement unit integrated within a helicopter-towed airborne platform. The attitude data are used to correct the time series for motional noise and subsequently to rotate into an earth-fixed reference frame. In a second processing step, and as opposed to existing semi-AEM systems, we transform the data into the frequency domain and estimate the complex-valued transfer functions between the received magnetic field components and the synchronously recorded injection current by regression analysis. This approach is similar to the procedure used in controlled-source EM. For typical source bipole moments of 20–40 kAm and for rectangular current waveforms with a fundamental frequency of approximately 10 Hz, we can estimate reliable three-component (3C) transfer functions in the frequency range from 10 to 5000 Hz over a measurement area of [Formula: see text] for a single source installation. The system has the potential to be used for focused exploration of deep targets.

The science mission of SpaceIL’s Beresheet lander

SpaceIL’s lunar lander mission Beresheet was launched on February 22, 2019 and impacted its targeted landing site in Mare Serenitatis on the Moon on April 11, 2019. The spacecraft carried a package of scientific instruments including a fluxgate magnetometer and a retroreflector array for laser ranging, as well as a suite of cameras. Orbital measurements of the magnetic field from Kaguya and Lunar Prospector guided the selection of the landing site to a location west of Posidonius crater in the Serenitatis plains, where the magnitude of the modeled magnetic field reaches 8–10 ​nT ​at the surface. Data was collected by the SILMAG magnetometer from Earth orbit, lunar orbit, and during the descent maneuver, although its interpretation is hindered by the presence of a spacecraft field.

Ultra-low frequency (ULF) magnetic field emissions associated with some major earthquakes occurred in Indian Subcontinent

We have analyzed ULF magnetic field emissions data obtained from identical 3- component search coil magnetometers installed at Indian stations of Agra (Geograph. lat. 27.2°N, long. 78°E), Shillong (25.92oN, 91.88oE), and Kachchh (23.78oN, 71oE) for the months of April 2012 and September 2013 in which three major earthquakes occurred, one of magnitude M = 8.5 in Indonesian region and two of magnitudes M = 7.4 and 6.8 in Pakistan. The results of the analysis show the occurrence of ULF bursts 09-16 days prior to the occurrence of these earthquakes at Agra and Shillong stations. Such bursts are not observed at Kachchh station. Analysis of ULF data obtained from a flux gate magnetometer at a remote station Kakioka in Japan (Geograph. lat. 36.2oN, long. 140.2oE) does not show such burst also. The bursts contain electromagnetic pulses of periods 10–15s (f = 0.06–0.1 Hz). The origins of these bursts in lithospheric sources (earthquakes) are confirmed by polarization parameter analysis of data. These ULF data are not influenced by lightning and magnetic storms. A long period analysis of the ULF data for the same months between the years 2010 and 2017 shows that occurrence of such bursts are characterized by either large magnitude shallow depth earthquakes (M > 6) or multiple shallow depth earthquakes of low magnitudes (M < 6). The precursory periods of the recorded ULF bursts match very well with those reported by Singh et al. (2018) who analyzed very low frequency (VLF) and ionospheric total electron content (TEC) data recorded at Agra station.

Optimization of the Temperature Stability of Fluxgate Sensors for Space Applications

Fluxgate magnetometers are widely used in many places for the measurement of weak magnetic field, but are sensitive to variations of sensor temperature. Therefore, their stabilization against temperature variation is required especially for outdoor applications. In this work, temperature dependencies of fluxgate sensors having the cores of one homemade, one commercially obtained finemet alloy, and a commercially obtained supermalloy alloy in ribbon form were examined. It was observed that the heat treatments of the studied cores affect the sensitivity of the sensors in different ways. For instance, while the scale factor of the sensor with the core from in-house prepared finemet ribbon increased from 1.19 MV/T to 3.12 MV/T, the scale factor of the sensor with the supermalloy core increases by 20 times in magnitude (41.6 kV/T to 0.92 MV/T) after heat treatment. Our analysis performed in the temperature interval from −50 °C to +85 °C reveals that temperature dependencies of the sensors also show differences depending on the core material. In addition to differences seen on the temperature dependence of the studied cores, the most stable one was the sensor with the heat treated in-house prepared finemet core. The variation of the scale factor in the 135 °C temperature range was 9.8 %. However, by analyzing the temperature dependences of the scale factors we could decrease the error coming from temperature variations to less than 1.0 % in magnitude of the output signal due to the observed linear dependence between the scale factor and the temperature of this sensor.

The Origin of Observed Magnetic Variability for a Sol on Mars From InSight

AbstractDay‐night variations in the magnetic field at Mars have been previously observed at satellite altitudes. The InSight Fluxgate Magnetometer (IFG) has provided the first evidence for diurnal magnetic field variations at the martian surface. IFG data show diurnal variations with typical peak amplitudes of 20–40nT in the early morning to midmorning; the amplitude of the magnetic field varies over the first 389 sols of the mission and peaks between sols 50 and 100. Temperature variations, solar array currents, and lander activities all generate magnetic fields. Particularly, the first two of these also produce signals with clear diurnal variations. We first assess the IFG data calibration and conclude that temperature and solar array currents have only minimal effects on the variability we observe in the final calibrated magnetic field data. We use satellite magnetic field data and a Mars global circulation model to make predictions for the temporal evolution of wind‐driven fields in the ionosphere. Such fields vary due to seasonal changes in the ionization profile and the winds, and in the altitude range of the dynamo region, that is, the region in which electric currents can be produced. We find that the amplitude and seasonal variability of the surface magnetic fields are generally consistent with those predicted from wind‐driven currents. Moreover, a regional dust storm in the vicinity of the InSight landing site, which started around sol 45, might be responsible for the higher magnetic field amplitudes observed in the IFG data in the early part of the mission.

Flight Calibration of the Van Allen Probe Magnetometers

Abstract The twin Van Allen Probes each carry a triaxial fluxgate magnetometer. Their orbits transverse a large of range of magnetic intensity. A procedure is described that calibrates the magnetometer in the spinning-spacecraft frame and in the presence of a persistent gradient of the magnetic field. This is done by extending a model based on a constant background magnetic field to a model with a changing magnetic field during intervals used for calibration. Model parameters derived from short intervals are obtained by direct calculation, and uncertainties are propagated throughout the analysis. A daily ensemble analysis of interval-derived parameters and uncertainties is then made to correct for sensor bias and misalignment. The whole analysis is iterated to convergence in a few steps based on the estimated uncertainties associated with the model parameters.

Commissioning of the multiparametric geophysical observatory at Shoal Bay, South Andaman and the preliminary results

The Indian Institute of Geomagnetism (IIG) is operating Multiparametric Geophysical Observatory (MPGO) at Port Blair in South Andaman. We report here on the commissioning of MPGO and the quality of data collected by this observatory. The base line values are regularly computed with the aid of the declination inclination magnetometer, in house developed proton precession magnetometer and the flux gate magnetometer. The total field computed by the vector magnetometer is all time compared with direct measurements from the scalar magnetometer. An attempt to co-relate the precursor seismo-electromagnetic emissions of the earthquake event by the induction coil magnetometer is made. The seismic station of the observatory is capable of recording seismic events within the vicinity of ≈200 km. Further MPGO is upgrading and some more experiments are planned for the future.

Dipole Fit Localization of the Deep Brain Stimulation Electrode Using 3D Magnetic Field Measurements

The aim of this study is to localize the electrode of the deep brain stimulation with three dimensional magnetic field measurements by applying the dipole fitting approach. The deep brain stimulation electrode was positioned successively at five increasing depths with well-known positions in a cylindrical head phantom and the magnetic field distribution was measured with a fluxgate magnetometer around the phantom. At each measuring point, the total magnetic field was measured by rotating the sensor in all three orthogonal directions. Finite element method was used to model the volume conduction of the phantom with its exact dimensions and electromagnetic simulations were performed to calculate the magnetic field distribution at the same measuring points around the phantom. The dipole fitting approach was then used to localize the position of the electrode by means of minimizing the normalized root mean square error between measured and calculated data. The results show an average localization accuracy of less than 1 mm over all performed measurements for both near surface and deep positions. Small deviations in the results can be explained by the measuring accuracy of the used fluxgate sensor. It can be concluded that the deep brain stimulation electrode can be precisely localized by three dimensional magnetic field measurements by using an accurate head volume conduction model and by applying the dipole fitting approach. The presented results are intended as preparatory work for real magnetic field measurements with patients implanted with deep brain stimulation electrodes.

Construction of a Fluxgate Magnetic Gradiometer for Integration with an Unmanned Aircraft System

The use of unmanned aircraft systems (UASs) for geophysical exploration and environmental monitoring allows for flexible, quick, and effective surveys with high-resolution results. Developing and integrating a magnetic gradiometer with a UAS allows for geophysical exploration of magnetic subsurface features such as geologic structures, metal detection, or locating unexploded ordinances (UXOs). This paper presents the development of a magnetic gradiometer for integration with a UAS. The magnetic gradiometer is composed of two fluxgate magnetometers, two GPS receivers, and a microcontroller-based controlling and data-logging system. The components of the magnetic gradiometer system are lightweight and inexpensive, ideal for use with a UAS. Initial field tests for the magnetic gradiometer are discussed. The initial results demonstrate the magnetic gradiometer’s data coherency along with future improvements that will improve the design of the instrument.

Evaluation of possible corrosion enhancement due to telluric currents: case study of the Bolivia–Brazil pipeline

Abstract. The electric field induced in the Bolivia–Brazil gas pipeline (GASBOL) was calculated by using the distributed source line transmission (DSLT) theory during several space weather events. We used geomagnetic data collected by a fluxgate magnetometer located at São José dos Campos (23.2∘ S, 45.9∘ W). The total corrosion rate was calculated by using the Gummow (2002) methodology and was based on the assumption of a 1 cm hole in the coating of the pipeline. The calculations were performed at the ends of pipeline where the largest “out-of-phase” pipe-to-soil potential (PSP) variations were obtained. The variations in PSP during the 17 March 2015 geomagnetic storm have led to the greatest corrosion rate of the analyzed events. All the space weather events evaluated with high terminating impedance may have contributed to increases in the corrosion process. The applied technique can be used to evaluate the corrosion rate due to the high telluric activity associated with the geomagnetic storms at specific locations.

The Experimental Albertan Satellite #1 (Ex-Alta 1) Cube-Satellite Mission

The Experimental Albertan satellite #1 (Ex-Alta 1) was a three-unit cube satellite (CubeSat) developed at the University of Alberta (UAlberta). As the first ‘made in Alberta’ spacecraft, the Ex-Alta 1 CubeSat was the Canadian contribution to the international QB50 CubeSat constellation mission ( www.qb50.eu ). Ex-Alta 1’s mission incorporated four science objectives, two technical objectives, and one educational outreach objective. These are reviewed in the context of the Ex-Alta 1 mission design, as well as future CubeSat constellation missions that may follow demonstration missions such as Ex-Alta 1 and the experiences of the QB50 project. In support of its objectives, Ex-Alta 1 flew the multi-needle Langmuir probe (m-NLP) QB50 standardized payload, a UAlberta developed miniaturized digital fluxgate magnetometer (DFGM) mounted on a two-element articulated deployable boom, a radiation dosimeter from Teledyne, and an open source onboard computer (OBC) developed at UAlberta. Ex-Alta 1 was released by a NanoRacks deployer from the International Space Station on May 26, 2017, and commanded and controlled from a ground-station developed and operated at UAlberta. Ex-Alta 1 operated continuously throughout its mission until it burned up in the atmosphere on November 14, 2018. The last two-way contact occurred on that day at 07:49:29 UTC, when the spacecraft reported an onboard temperature of 47 °C in eclipse at an altitude of 152 km and which marked the effective end of the mission. This paper provides an overview of the Ex-Alta 1 mission, its development, the spacecraft and mission design, and reports preliminary results from the payload focusing on the DFGM instrument. We also report briefly on related education and outreach activities, including the development and delivery of curriculum-targeted and CubeSat focused classroom sessions inspired by the Ex-Alta 1 mission to school pupils in Alberta.

The First Pi2 Pulsation Observed by China Seismo-Electromagnetic Satellite

On 2 February 2018, the China Seismo-Electromagnetic Satellite (CSES) ZhangHeng 01 (ZH-01) was successfully launched, carrying on board, in addition to a suite of plasma and particle physics instruments, a high precision magnetometer package (HPM), able to observe the ultra-low frequency (ULF) waves. In this paper, a night time Pi2 pulsation observed by CSES is reported for the first time. This Pi2 event occurred on 3 September 2018, and began at 14:30 UT (02:37 magnetic local time), when the satellite was in the southern hemisphere between −49 and −13 magnetic latitude (MLAT). Kakioka (KAK) ground station in Japan detected the same Pi2 between 14:30–14:42 UT (23:30–23:42 local time). The Pi2 oscillations in the compressional, toroidal, and poloidal components at the CSES satellite and the H-component at the KAK station are investigated by estimating coherence, amplitude, and cross-phase. We noticed a high degree of similarity between the Pi2 event in the horizontal component at KAK and the ionospheric fluctuations in the compressional component at CSES. This high correlation indicated the magnetospheric source of the Pi2 event. In addition, Pi2 is exhibited clearly in the δBy component at CSES, which is highly correlated with the ground H component, so the Pi2 event could be explained by the Substorm Current Wedge (SCW). This interpretation is further confirmed by checking the compressional component of Van Allen Probe (VAP) B satellite inside the plasmasphere, which, for the first time, gives observational support for an earlier model. This ULF wave observation shows the consistency and reliability of the high precision magnetometer (HPM) equipped by two fluxgate magnetometers (FGM1 and FGM2) onboard CSES.

Magnetometer in-flight offset accuracy for the BepiColombo spacecraft

Abstract. Recently the two-spacecraft mission BepiColombo launched to explore the plasma and magnetic field environment of Mercury. Both spacecraft, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO, also referred to as Mio), are equipped with fluxgate magnetometers, which have proven to be well-suited to measure the magnetic field in space with high precision. Nevertheless, accurate magnetic field measurements require proper in-flight calibration. In particular the magnetometer offset, which relates relative fluxgate readings into an absolute value, needs to be determined with high accuracy. Usually, the offsets are evaluated from observations of Alfvénic fluctuations in the pristine solar wind, if those are available. An alternative offset determination method, which is based on the observation of highly compressional fluctuations instead of incompressible Alfvénic fluctuations, is the so-called mirror mode technique. To evaluate the method performance in the Hermean environment, we analyze four years of MESSENGER (MErcury Surface, Space ENvironment, GEophysics and Ranging) magnetometer data, which are calibrated by the Alfvénic fluctuation method, and compare it with the accuracy and error of the offsets determined by the mirror mode method in different plasma environments around Mercury. We show that the mirror mode method yields the same offset estimates and thereby confirms its applicability. Furthermore, we evaluate the spacecraft observation time within different regions necessary to obtain reliable offset estimates. Although the lowest percentage of strong compressional fluctuations are observed in the solar wind, this region is most suitable for an accurate offset determination with the mirror mode method. 132 h of solar wind data are sufficient to determine the offset to within 0.5 nT, while thousands of hours are necessary to reach this accuracy in the magnetosheath or within the magnetosphere. We conclude that in the solar wind the mirror mode method might be a good complementary approach to the Alfvénic fluctuation method to determine the (spin-axis) offset of the Mio magnetometer.

Analysis of Eddy Current Generation on the Juno Spacecraft in Jupiter's Magnetosphere

AbstractThe Juno mission to Jupiter, in polar orbit around the gas giant since 4 July 2016, samples the planet's environment with dedicated particle and fields instruments. Juno's magnetometer investigation employs a pair of boom‐mounted vector fluxgate magnetometers colocated with a set of star cameras to map Jupiter's magnetic field with high accuracy. Juno is a spinning spacecraft, rotating at approximately two rotations per minute. In strong magnetic field environments experienced near periapsis, Eddy currents are generated within electrically conductive material near the magnetic sensors. These currents adversely affect measurements of the environment, most evident in the appearance of a spin modulation in the field magnitude. We demonstrate, by finite element modeling and laboratory measurements, that the spin modulation is caused by a physical signal due to Eddy currents generated by the rotation of the conductive spacecraft structure in the presence of a strong magnetic field. We present a finite element model of the induced field and develop a matrix method for removing the Eddy current contribution to the measured field. Juno magnetic field measurements in strong fields are corrected for Eddy current contributions using this model of the interaction.

Aerial magnetic mapping with an unmanned aerial vehicle and a fluxgate magnetometer: a new method for rapid mapping and upscaling from the field to regional scale

ABSTRACTMagnetic measurements with an unmanned aerial vehicle are ideal for filling the gap between ground and airborne magnetic surveying. However, to obtain accurate aeromagnetic data, the compensation of magnetic effects of the unmanned aerial vehicle is a challenge. Typically, scalar magnetometers are towed several metres under the unmanned aerial vehicle to minimize its magnetic field. In this study, a fluxgate three‐component magnetometer is attached 42 cm in front of the unmanned aerial vehicle at the tip of a composite pipe. Using a scalar calibration, the sensor can be calibrated, and the permanent and induced magnetic fields of the unmanned aerial vehicle can be compensated. The contributions of the magnetic measurements at different altitudes to the unmanned aerial vehicle results were tested over an area of 1 km² in the Northern Vosges Mountains. The area is located in a hamlet surrounded by a forest where few geological outcrops are observed. Three magnetic surveys of the same area are obtained at different altitudes: 100, 30 and 1 m above the ground. The unmanned aerial vehicle magnetic data are compared with a helicopter aeromagnetic survey at 300 m above the ground and a ground magnetic survey using upward continuations of the maps to compare the results. The magnetic maps (300, 100, 30 and 1 m above the ground) show very different magnetic anomaly patterns (e.g. amplitude, shape, wavelength and orientation). The magnetic data at different altitudes improve the understanding of the geology from the local to more general scales.

The Acceleration of Lunar Ions by Magnetic Forces in the Terrestrial Magnetotail Lobes

AbstractIn order to study the acceleration of ions originating from the tenuous exosphere and surface of the Moon, we analyzed data from the ElectroStatic Analyzer (ESA) and Flux Gate Magnetometer (FGM) carried by the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. Previous investigations have modeled the acceleration of lunar ions by the motional electric field of the surrounding plasma. However, in the terrestrial magnetotail, where the lunar ion density can equal or even exceed the ambient plasma density, other forces may play an important role in the tenuous plasma environment. Determining what forces govern lunar ion motion is important in understanding their interaction with the ambient plasma in the unique environment of the magnetotail. Based on a detailed analysis of two individual ARTEMIS observations, we find that magnetic pressure and magnetic tension forces may play an important role in accelerating the lunar ions.