Magnetometer Data Research Articles

Integrated space\u2013frequency\u2013time domain feature extraction for MEG-based Alzheimer\u2019s disease classification

Magnetoencephalography (MEG) has been combined with machine learning techniques, to recognize the Alzheimer’s disease (AD), one of the most common forms of dementia. However, most of the previous studies are limited to binary classification and do not fully utilize the two available MEG modalities (extracted using magnetometer and gradiometer sensors). AD consists of several stages of progression, this study addresses this limitation by using both magnetometer and gradiometer data to discriminate between participants with AD, AD-related mild cognitive impairment (MCI), and healthy control (HC) participants in the form of a three-class classification problem. A series of wavelet-based biomarkers are developed and evaluated, which concurrently leverage the spatial, frequency and time domain characteristics of the signal. A bimodal recognition system based on an improved score-level fusion approach is proposed to reinforce interpretation of the brain activity captured by magnetometers and gradiometers. In this preliminary study, it was found that the markers derived from gradiometer tend to outperform the magnetometer-based markers. Interestingly, out of the total 10 regions of interest, left-frontal lobe demonstrates about 8% higher mean recognition rate than the second-best performing region (left temporal lobe) for AD/MCI/HC classification. Among the four types of markers proposed in this work, the spatial marker developed using wavelet coefficients provided the best recognition performance for the three-way classification. Overall, the proposed approach provides promising results for the potential of AD/MCI/HC three-way classification utilizing the bimodal MEG data.

Magnetic gradiometry using frequency-domain filtering

Accurate measurements of ambient planetary and interplanetary magnetic fields using spacecraft magnetometers typically require accounting for interfering magnetic fields generated by the flight system (FS). The most common method for removing FS-generated time-variable magnetic fields is narrow-band and low-pass filtering of magnetic field data in the frequency domain. However, if fluctuations in the ambient field contain frequencies overlapping those in the FS field, it can be difficult to construct a filter that will not affect both signals. Here we present an alternate method for removing FS time-variable signatures from magnetic field measurements. For spacecraft that make use of a magnetic gradiometer (i.e. with two or more instruments on a boom at different distances from the center of the spacecraft), the dominant frequencies in the FS field can be identified using spectra of the differenced field components. The amplitudes of the FS field at those frequencies can then be suppressed without removing spectral peaks present in the ambient field. We demonstrate the successful application of this method, referred to as gradiometry peak suppression, both to modeled data sets and to 128 Hz Venus Express magnetometer data.

The Global Conductivity Structure of the Lunar Upper and Midmantle

AbstractMagnetic sounding is a powerful tool to explore the interior of planetary bodies through the electrical conductivity structure. The electrical conductivity structure of the lunar mantle has previously been derived from surface magnetic field measurements as part of the Apollo 12 mission and concurrent magnetometer data acquired from orbit through the Explorer 35 satellite. Here, we derive the first global conductivity structure of the upper and midmantle using only satellite magnetometer data collected by the recent Lunar Prospector and Kaguya Selene satellite missions. We show that the field in the geomagnetic tail exhibits a simple geometrical structure and can be well described by a single spherical harmonic of degree and order one. Employing this information about the inducing field geometry and assuming a potential representation of the field in the geomagnetic tail, we derive a frequency‐dependent transfer function and invert it for a one‐dimensional (1‐D) electrical conductivity profile of the lunar upper and midmantle. Our global transfer function shows striking similarity with the local one obtained from joint analysis of Apollo 12 and Explorer 35 magnetometer data. This indicates the lack of local variations at the Apollo 12 landing site compared to the globally averaged upper to midmantle electrical conductivity structure.

PSII-12 Identifying behaviors and the ‘normal’ daily ethogram using accelerometers on grazing animals

Abstract Animal behavior plays a crucial role as an indicator of animal health and nutritional status and serves as an indicator of animal growth. The objective of this study was to build an ethogram describing behavior in grazing cattle. We collected video and accelerometer data from crossbred steers (n = 10) used as part of a larger grazing study on the HH Leveck Animal Research Center, Mississippi State, MS. Daily Diary accelerometers (Wildbyte® technologies, Swansea) were programmed to collect magnetometer and accelerometer data at 40 Hz and attached to the GPS collars fitted on the animals prior to their release into a 10-hectare pasture of Tall Fescue and Bermudagrass, overseeded with Annual Ryegrass. Automated camera traps (Bushnell Essential®) were synced with UTC time and programmed to record 30-second video clips when triggered. Approximately 387,000 accelerometer signals representing 161 minutes of behavior from 10 animals were recorded, and behavior classified according to 1 of 5 categories: traveling, foraging, resting, ruminating, and grooming (Kilgour et al., 2012). Categorized accelerometer data was used to train a random forest model (Liaw and Weiner, 2002) in Program R (R Core Team, 2020), which resulted in a model sensitivity of 0.97, 0.93, 0.90, 0.87, and 0.80 for Traveling, Foraging, Resting, Ruminating, and Grooming, respectively, and an overall model accuracy of 0.95. Behaviors were aggregated into behavior bouts, and a daily ethogram was calculated for March 2019. This revealed that the steers spent the most amount of time traveling, an average of 1,026 minutes per day. This behavior was followed, in the average length of time, by foraging and resting for 205 ± 52.8 minutes and 31.8 ± 28.2 minutes per day, respectively. These results indicate the ability to accurately build a behavioral ethogram for grazing cattle and warrant further study in future research and livestock management.

Case Studies of Ionospheric Plasma Irregularities Over Queen Maud Land, Antarctica

AbstractWe use the first data set from the ground‐based TEC and scintillation receiver located at the Norwegian Research Station Troll in Queen Maud Land, Antarctica to analyze in detail the ionospheric response during geomagnetic disturbances on February 26–27 and March 18–19, 2018. By combining the Troll data with complementary measurements (scintillation receivers, magnetometers, SuperDARN, DMSP satellites), we demonstrate that plasma irregularities above this part of Queen Maud Land can be associated with the expansion of the auroral oval, related structuring on its edges, as well as with strong flow shears in the evening and at nighttime, which are further modulated by the energetic particle precipitation. Phase scintillation indices correlate well with the magnetometer data.

ULF Waves Observed by Lunar Prospector

AbstractWe have studied the spatial distribution of ultra‐low frequency (ULF) in the vicinity of the Moon using Lunar Prospector (LP) magnetometer data obtained at ∼100 km altitude during the period from February 20, 1998 to November 30, 1998. The lunar ULF waves are mostly identified over a broad frequency range of 10–60 mHz in the spacecraft frame. The occurrence rate of the ULF wave is high on the dayside above strong magnetic anomalies and depends on the interplanetary magnetic field orientation. We examine wave properties including the wave propagation direction and polarization. They are very similar to Kaguya observations, indicating that the ULF waves observed at LP and Kaguya are generated by the same mechanism. Although lunar ULF waves are commonly observed on the dayside above lunar magnetic anomalies, how they are established as a regular oscillation is not completely understood. In the present study, we suggest that the electromagnetic ion beam instability, driven by protons reflected from lunar magnetic anomalies, is the likely source of ULF waves observed at LP.

Prediction of Labor Activity Recognition in Construction with Machine Learning Algorithms

It is essential that the control and management of the work of labors in construction project management is effective. In this study, it is aimed to building artificial intelligence models to recognition on activities in a construction work to effectively utilization project management and control. In accordance with this purpose, 3-axis accelerometer, gyroscope, and magnetometer data were obtained from the labors through the sensor to predict the activities determined for a construction work. These raw data were made compliance for the model by going through a series of preprocessing applications. These data are trained and modeled with basic machine learning algorithms logistic regression, SVC, DT and KNN algorithms. According to the results of the analysis, the best prediction was obtained with the SVC algorithm with an accuracy of 90%. In other algorithms, respectively, 87% accuracy was contrived in the KNN algorithm, and approximately 80% accuracy in the logistic regression and DT algorithms. According to these values, it has been observed that the activities performed in a construction work can be estimated at a high rate. In this way, at the construction sites, it can be automatically determined which work the laborer do at a certain accuracy rate.

Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby

Abstract. Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the YVSO direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (SERENA-PICAM) of the SERENA suite, the Mercury Electron Analyser (MEA), and the BepiColombo Radiation Monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with e.g. strong flapping motions at a period of ∼7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.

New Findings of the Sporadic E (Es) Layer Development Around the Magnetic Equator During a High‐Speed Solar (HSS) Wind Stream Event

AbstractThe equatorial (Esq) and blanketing (Esb) sporadic (Es) layers occur due to the Equatorial Electrojet Current (EEJ) plasma instabilities and tidal wind components, respectively. Both Esq and Esb layers can appear concurrently over some Brazilian equatorial regions due to the peculiar geomagnetic field configuration in this sector. Previous works indicate that the inclination angle limit for the Esq occurrence in ionograms is 7°. However, we found evidence that regions more distant can also experience such equatorial dynamics during disturbed periods. In this context, we deeply investigated this EEJ influence expansion effect by analyzing the Esq layers in regions not so close to the magnetic equator during a high‐speed solar wind stream event that occurred on May 05 and 06, 2018. To explain these atypical Esq layer occurrences, we considered the Es layer parameters obtained from digital ionosondes over the Brazilian regions, São Luís (dip: 9.5°), and Araguatins (dip: 10.5°). We use magnetometer data and a model named MIRE (E Region Ionospheric Model) to validate this mechanism. The results show that the eastward electric field of the Gradient Drift instability in the EEJ is effective during the magnetic storm main phase in the boundary equatorial magnetic sites, creating the Esq layers. Thus, the EEJ plasma irregularity superimposes the wind shear mechanism, changing the Es layer dynamics during disturbed periods over the magnetic equator boundary sites. Therefore, this work establishes new findings of the EEJ influence expansion dynamics in the Es layer formation over the Brazilian regions, which was considered in MIRE for the first time.

Magnetometer Calibration Based on the CHAOS-7 Model

We describe a method for the in-orbit calibration of body-mounted magnetometers based on the CHAOS-7 geomagnetic field model. The code is designed to find the true calibration parameters autonomously by using only the onboard magnetometer data and the corresponding CHAOS outputs. As the model output and satellite data have different coordinate systems, they are first transformed to a Star Tracker Coordinate (STC). Then, non-linear optimization processes are run to minimize the differences between the CHAOS-7 model and satellite data in the STC. The process finally searches out a suite of calibration parameters that can maximize the model-data agreement. These parameters include the instrument gain, offset, axis orthogonality, and Euler rotation matrices between the magnetometer frame and the STC. To validate the performance of the Python code, we first produce pseudo satellite data by convoluting CHAOS-7 model outputs with a prescribed set of the ‘true’ calibration parameters. Then, we let the code autonomously undistort the pseudo satellite data through optimization processes, which ultimately track down the initially prescribed calibration parameters. The reconstructed parameters are in good agreement with the prescribed (true) ones, which demonstrates that the code can be used for actual instrument data calibration. This study is performed using Python 3.8.5, NumPy 1.19.2, SciPy 1.6, AstroPy 4.2, SpacePy 0.2.1, and ChaosmagPy 0.5 including the CHAOS-7.6 geomagnetic field model. This code will be utilized for processing NextSat-1 and Small scale magNetospheric and Ionospheric Plasma Experiment (SNIPE) data in the future.

P-T-D evolution of the southeast Passo Feio Complex and the meaning of the Caçapava Lineament, Dom Feliciano Belt, southernmost Brazil

Metamorphic–deformation paths and interpretations of regional structures are essential for the understanding of how orogens evolve. While in active orogens, structures can be easily mapped for hundreds of kilometres, regional structures in ancient mountain belts may appear only as subsurface geophysical data. In this paper, we constrain the metamorphic–deformation history of the southeastern part of the Passo Feio Complex located in the Neoproterozoic Dom Feliciano Belt in southernmost Brazil. The complex is crosscut by a block-limiting structure defined by magnetometric data, the Caçapava Lineament. Our petrographic interpretations and thermodynamic modelling of pelitic schists of the Passo Feio Complex indicate the beginning of garnet growth at ca. 530–550 °C and 3–4.3 kbar during D1, and metamorphic peak at ca. 560–570 °C and 5–5.5 kbar (M1), during progression to D2. After M1 (~17–19 km depth), the complex was exhumed to at least 14 km (~4 kbar) depth, as the contact metamorphism by the Caçapava Granite (ca. 562 Ma) produced andalusite. The correlation of D3 structures of the Passo Feio Complex (S3 and L3), magmatic structures in the Caçapava Granite, orientation of geophysical anomalies in the region and kinematics of S3 corroborate the interpretation of the Caçapava Lineament as a dextral shear zone. Due to the location of anomalies and previous three-dimensional modelling of the granitic body, we interpret that a curved ENE to NS branch of the NE-striking Caçapava Shear Zone is responsible for the accommodation of the Caçapava Granite. Lastly, we discuss the regional implications of such interpretation, which brings up the question of block-limiting character of the Caçapava Shear Zone and the geotectonic position of the Passo Feio Complex.

Characterization of Transient‐Large‐Amplitude Geomagnetic Perturbation Events

AbstractWe present a characterization of transient‐large‐amplitude (TLA) geomagnetic disturbances that are relevant to geomagnetically induced currents (GIC). TLA events are defined as one or more short‐timescale (<60 s) dB/dt signature with magnitude ≥6 nT/s. The TLA events occurred at six stations of the Magnetometer Array for Cusp and Cleft Studies throughout 2015. A semi‐automated dB/dt search algorithm was developed to identify 38 TLA events in the ground magnetometer data. While TLA dB/dts do not drive GICs directly, we show that second‐timescale dB/dts often occur in relation to or within larger impulsive geomagnetic disturbances. Sudden commencements are not the main driver, rather the events are more likely to occur 30 min after a substorm onset or within a nighttime magnetic perturbation event. The characteristics of TLA events suggest localized ionospheric source currents that may play a key role in generating some extreme geomagnetic impulses that can lead to GICs.

Iridium Communications Satellite Constellation Data for Study of Earth's Magnetic Field

AbstractCharacterization of Earth's magnetic field is key to understanding dynamics of the core. We assess whether Iridium Communications magnetometer data can be used for this purpose since. The 66 Iridium satellites are in 86° inclination, 780 km altitude, circular orbits, with 11 satellites in each of six orbit planes. In one day the constellation returns 300,000 measurements spanning the globe with <2° spacing. We used data from January 2010 through November 2015, and compared against International Geomagnetic Reference Field (IGRF‐11) to inter‐calibrate all data to the same model. Geomagnetically quiet 24‐h intervals were selected using the total Birkeland current, auroral electrojet, and ring current indices. The z‐scores for these quantities were combined and the quietest 16 intervals from each quarter selected for analysis. Residuals between the data and IGRF‐11 yield consistent patterns that evolve gradually from 2010 to 2015. Residuals for each day were binned in 9° latitude by 9° longitude and the distributions about the mean in each bin are Gaussian with 1‐sigma standard errors of ∼3 nT. Spherical harmonic coefficients for each quiet day were computed and time series of the coefficients used to identify artifacts at the orbit precession (8 months) and seasonal (12 months) periods and their harmonics which were then removed by notch filtering. This analysis yields time series at 800 virtual geomagnetic observatories each providing a global field map using a single day of data. The results and CHAOS 7.4 generally agree, but systematic differences larger than the statistical uncertainties are present that warrant further exploration.

On the Geomagnetic Field Line Resonance Eigenfrequency Variations during Seismic Event

In this paper, we report high statistical evidence for a seismo–ionosphere effects occurring in conjunction with an earthquake. This finding supports a lithosphere-magnetosphere coupling mechanism producing a plasma density variation along the magnetic field lines, mechanically produced by atmospheric acoustic gravity waves (AGWs) impinging the ionosphere. We have analysed a large sample of earthquakes (EQ) using ground magnetometers data: in 28 of 42 analysed case events, we detect a temporary stepwise decrease (Δf) of the magnetospheric field line resonance (FLR) eigenfrequency (f*). Δf decreases of ∼5–25 mHz during ∼20–35 min following the time of the EQ. We present an analytical model for f*, able to reproduce the behaviour observed during the EQ. Our work is in agreement with recent results confirming co-seismic direct coupling between lithosphere, ionosphere and magnetosphere opening the way to new remote sensing methods, from space/ground, of the earth seismic activity.

Penentuan Orientasi dan Translasi Gerakan UAV menggunakan Data Fusion berbasis Kalman Filter

In an unmanned aircraft vehicle, a navigation system is needed to calculate its orientation and translation. The navigation system can utilize data from the accelerometer, gyroscope, magnetometer, and GPS. The orientation can be precisely calculated from the accelerometer and magnetometer data when the sensor is in a static state. Meanwhile, under dynamic conditions, the orientation can be more precisely calculated from the gyroscope data. In order to obtain the robust navigation system, a data fusion based on Kalman filter is built to calculate the orientation from the accelerometer, gyroscope, and magnetometer. The Kalman filter trusts more in the data from the accelerometer and magnetometer when the UAV is static and trusts more in to the gyroscope data when the UAV is in dynamic conditions. Meanwhile, the UAV translation is obtained by performing data fusion of the accelerometer data with location data from the GPS sensor. The Kalman filter combines data from the accelerometer and GPS when available, otherwise trusts in data from the accelerometer only. The trust level shifting is done by changing the measurement noise covariance. The data fusion based on Kalman filter provides more accurately the orientation and translation data. The orientation as a result of the calculation from the gyroscope has an average error of 18.12%, while the orientation as a result of the accelerometer and magnetometer has an error of 1.3%. By using Kalman filter-based data fusion, the error of the orientation decreases to 0.87%

Morphology and magnetic properties of NiFe2O4 powders prepared in molten sodium chloride

AbstractNiFe2O4 powders were successfully fabricated at different temperatures by using molten salt method and their structure and magnetic properties were investigated by using x‐ray diffractometer, scanning electron microscope and vibrating sample magnetometer. The x‐ray diffractometer result shows that all powders are single spinel phase, scanning electron microscope image indicates that the grain mainly has an octagonal shape and the average particle size increases with increasing sintering temperature. The vibrating sample magnetometer data reveal that saturation magnetization of NiFe2O4 powders increases, while coercivity decreases with increasing sintering temperature.

Complex magnetic ordering in RE5Pd2In4 (RE = Tb-Tm) compounds investigated by neutron diffraction and magnetometric measurements

The RE5Pd2In4 (RE = Tb-Tm) compounds crystallize with the orthorhombic Lu5Ni2In4-type crystal structure (Pbam space group). In this work we report results of structural and magnetic studies by means of X-ray and neutron diffraction as well as dc and ac magnetometric data. Magnetic susceptibility and neutron diffraction data revealed rare-earth moments order at low temperatures with complex magnetic structures showing a cascade of temperature-induced transitions. The magnetic ordering temperatures are found to be 97, 88, 28.5, 16.5 and 4.3 K for RE = Tb, Dy, Ho, Er and Tm, respectively. Magnetic structures related to the propagation vector k→1=[0,0,0] are found just below the magnetic ordering temperatures in majority of the investigated compounds (RE = Tb-Er). Below the Curie temperature TC they have purely ferromagnetic character in Tb5Pd2In4 and Dy5Pd2In4. A ferrimagnetic order finally sets at lower temperatures in Dy5Pd2In4, while in Ho5Pd2In4 two magnetic phases related to k→1 are observed: the antiferromagnetic one (phase I) and the ferrimagnetic one (phase II, coexisting with phase I at lower temperatures). Er5Pd2In4 is a canted antiferromagnet with additional ferromagnetic component developing at lower temperatures. A purely antiferromagnetic component of magnetic structure with enlarged magnetic unit cell appears with decreasing temperature in Tb5Pd2In4 (k→2=[0,12,0] and k→3=[0,12,12]) while in Ho5Pd2In4 such component (k→4=[14,0,0]) is present within whole temperature range below the magnetic ordering temperature. Magnetic structure of Tm5Pd2In4, exceptionally, has no k→1 component, but is an antiferromagnetic incommensurate one related to two propagation vectors: k→5=[0.073(3),0.451(1),12] and k→6=[0,0.335(2),12]. In majority of the compounds (RE = Tb-Er) the first rare-earth 4g site (noted as 4g1) orders at lower temperature than two remaining sites (2a and 4g2). The direction of the magnetic moments depends on rare-earth element involved and indicates an influence of single-ion anisotropy in the crystalline electric field (CEF).

Philistine urban form at Tell es-Safi/Gath, Israel: a magnetometric perspective

Some scholars view Philistine settlement in the southern Levant as the dominant, colonizing imposition of a new urbanism following a period of small cities and structural realignment during the Late Bronze Age. Others view Philistine urbanism as a gradual process that marks emergent, rather than imposed, cities. Here we explore Philistine urban planning through magnetometer and excavation data from Tell es-Safi/Gath. Results show that the northern lower city has dense, symmetrical buildings bordering main streets, an industrial area, potential extra-mural settlement, and many burned structures. Comparing these results to planning in other Philistine cities, we argue that these cities were moderately planned because they have many shared features, an emphasis on ordered spaces, and possibly discrete locations for industrial activities, but spatial divisions and street widths were not rigidly enforced, and the relative location of specialized activities varies. This finding is consistent with the emergent model of Philistine urbanism.

A Modular Model of Jupiter's Magnetospheric Magnetic Field Based on Juno Data

AbstractAccurate modeling of Jupiter's magnetospheric magnetic field is important for not only scientific research but also mission planning. We develop a new empirical global model of Jupiter's magnetic field in the Juno era, including components from the planetary dynamo, Chapman‐Ferraro currents, and equatorial current sheet. The internal field is based on the JRM09 model. The shielding field is obtained by minimizing the component normal to Jupiter's magnetopause and varies due to the change of solar wind dynamic pressure. Combined with the curved magnetodisk, the high‐resolution TS07 method is used for modeling Jupiter's magnetodisc and tail currents. The best‐fitting results show an asymmetric magnetodisc current system in azimuthal direction with a tilted angle to Jupiter's magnetic equator. The sweep‐back effects of Jupiter's magnetic fields are also reproduced by the radial current system. This new model is validated by comparing with Juno's magnetometer data in the range from 5 Rj to 60 Rj, where Rj = 71,492 km is the radius of Jupiter.

Dayside Cusp Aurorae and Ionospheric Convection Under Radial Interplanetary Magnetic Fields

AbstractDayside cusp aurorae are created from particles precipitating into the cusp, and ionospheric convection is driven by solar wind electric fields. In this study, we coordinated the observations obtained from the all‐sky camera on Svalbard, the Super Dual Auroral Radar Network, SuperMAG magnetometer data, and far ultraviolet imagers on board the Defense Meteorological Satellite Program satellites for the event January 4, 2014 to examine the morphology of aurorae and the patterns of ionospheric convection for radial interplanetary magnetic field (IMF). During the event, a poleward‐moving auroral form and antisunward ionospheric convection were observed when the IMF turned into almost purely radial. Moreover, both types of antisunward and sunward convection were simultaneously observed near the footprint of the cusp at different times during the radial IMF period. The antisunward convection and sunward convection are typically an indicator of the dayside reconnection for the southward IMF and the lobe reconnection for the northward IMF, respectively. All those observations support the concept of low‐latitude dayside and high‐latitude lobe reconnection for the radial IMF. This study further shows that the coexistence of the two types of reconnection for radial IMF, resulting in an interplay of repetitive antisunward and sunward convection.