The magnetic gradient tensor system (MGTS) is disturbed by the measurement noise and electromagnetic field, which affects its accuracy of calibration and target tracking seriously. Hence, we proposed ...an improved variational modal decomposition (IVMD) noise-reduction method for the measurement and calibration of MGTS. First, continuously sampling around the center of MGTS to obtain a sufficient amount of three-axis magnetic component signals, and the total magnetic intensity (TMI) and cosine signals are vector-synthesized to avoid distortion. Then, the endpoint extension of the signal is performed using the spectral cyclic correlation coefficient, and variational modal decomposition (VMD) on the synthesized signal and kernel independent component analysis (KICA) are performed on its principal components to eliminate interference noise and modal aliasing. Finally, the system is calibrated with the integrated compensation and rotation alignment (ICRA) method to eliminate sensor systemic error, array misalignment error, and hard or soft magnetic interference. Experiments show that, compared with ICRA direct calibration, the proposed method reduces the root-mean-square error (RMSE) of the MGT component from 102.2 to 5.6 nT/m in the indoor electromagnetic field environment. In this scene, the tracking accuracy RMSE of the magnet target is reduced from 0.16 to 0.07 m.
The features of the geomagnetic noise distribution over frequencies in different bandwidths and in the signal accumulation mode are investigated. It is shown that the amplitude of geomagnetic noise, ...measured by a magnetomodulation magnetometer in the passband of 0.1 to 230 Hz at the latitude of the Middle Urals in a quiet geomagnetic field can vary from 0.2 to ~2 nT from peak-to-peak, depending on the time and place of the measurement. The conditions for measuring a weak magnetic field against a background of geomagnetic noise and the limitations associated with the random nature of the changes in the amplitude of geomagnetic noise and the lack of correlation of its amplitude at various measurement points are considered. The obtained data can be used to estimate the amplitude of a weak external magnetic field, which can be recorded in an undisturbed geomagnetic field in unshielded space, which is of interest in magnetobiology and biomedicine.
In this paper we introduce an end-to-end deep learning (DL) framework for magnetic anomaly detection (MAD) and denoising. This framework consists of two neural networks: a binary classification ...network for magnetic anomaly detection and a regression network for geomagnetic noise suppression. The two networks work in a cascade mode: the magnetic field measurement is first sent to the detection network to check the existence of the anomaly signal, and then to the denoising network for extracting the signal from the geomagnetic noise if the detection result is positive. The core idea of our proposed method is that the characteristics of both the magnetic anomaly signal and the geomagnetic noise can be learned from massive training data. The experimental results show that: (1) under the same false alarm rate constraint, the probability of detection of our proposed method is above 80% when the signal-to-noise ratio (SNR) equals −6 dB, while the orthogonal basis function (OBF) method fails when the SNR is below 0 dB; (2) for geomagnetic noise suppression, an improvement of 10 to 15 dB is achieved for data with input SNRs between −5 and 15 dB. Our results paved the way for data-driven magnetic anomaly detection and denoising.
The beginning of the 25th Solar Cycle and 2019 Winter Solstice was an entirely appropriate timeframe for conducting a study of the lunar impact on geomagnetic noise. At the end of 2019, we were able ...to perform a time series of geomagnetically calm days at the PIA observatory (Piran) during the three-day period from the Third Quarter to the New Moon, which almost coincided with the Winter Solstice. The results of the geomagnetic noise caused by the influence of the Moon can be used as a starting point for the investigation of other natural and anthropogenic influences on geomagnetic measurements at the geomagnetic observatory PIA (Piran). KEY WORDS geomagnetic noise, gravity of the Moon, 25th Solar cycle, Winter Solstice (ProQuest: ... denotes formulae omitted.) 1UVOD Zaradi vse večjega zavedanja, da popolná zanesljivost določitve položaja s tehnologijo GNSS zaradi naravnih ali namernih motenj signala ni mogoča, je v podporo za neprekinjeno določitev položaja treba poznati tudi druge rešitve.
In this work, the authors improve the magnetic anomaly detector by using Karhunen–Loeve expansion, for expanding the detection distance of visually obscured ferromagnetic object when the target ...signal is contaminated by coloured noise. In the detector, the orthonormal basis functions are modified by the autocorrelation function of geomagnetic noise, and the anomaly is detected by matched filtering. Compared with the traditional detector, simulation results show that the modified detector has better performance with coloured Gaussian noise; especially, the improvement is more evident when the noise exponent is bigger. The real geomagnetic noise is proved to be coloured and obey approximate Gaussian distribution by the measurements in experiment. Tests with this noise indicate that the proposed detector achieves an incremental detection probability of 0.1 – 0.2 in the case of low signal-to-noise ratio, which makes it more attractive in practice.
The article describes the issues involved in comparing the results of measurements of a weak magnetic field in an unshielded space with the use of sensors of various types, which is relevant for ...geophysics, magnetobiology, and medicine. The issues of measuring a weak variable magnetic field by various magnetic induction sensors in an unshielded space in the absence of obvious geomagnetic variations are considered. The amplitude of natural geomagnetic noise in a quiet geomagnetic field in the absence of geomagnetic variations is shown to have a random nature; therefore, gradient methods for measuring a weak variable magnetic field are limited from below by the level of natural geomagnetic noise. The influence of the size of the sensor of a weak variable magnetic field on the results of measurements of broadband random geomagnetic noise is identified.
We analyze the possibility of measuring of weak low-frequency alternating magnetic fields against the background of geomagnetic variations and estimate the lower limits of detection of weak periodic ...and aperiodic signals of magnetic induction in the geomagnetic field by magnetomodulation sensors. It is shown that the components of magnetic induction of continuous geomagnetic noise measured in a narrow frequency band by two magnetomodulation sensors located at a distance greater than one meter are random and independent.
The article presents the results of measurements of geomagnetic field variations obtained using magnetometers with different frequency range (0.01–200 Hz and 0.01–30 Hz) developed at the Institute of ...Geophysics of Uro RAS. The measurements showed that the sensitivity and resolution of the equipment used in the work is sufficient to study the variations of the geomagnetic field at low frequencies. It is shown that magnetometers used by magnetic modulation converter with auto-parametric amplification of the signal are capable of recording variations of the geomagnetic field that do not exceed the level of geomagnetic noise of 0.2 pT at a frequency of 2 Hz and 1 pT at lower frequencies. The average amplitude of the variations in the geomagnetic field of the magnetic induction components recorded by the device with a frequency range of 0.01–200 Hz in the entire bandwidth is twofold higher than the average amplitude of the magnetic induction components recorded by the device with a frequency range of 0.01–30 Hz, but the spectral composition shows close values.
The variation of geomagnetic field greatly increases the difficulty of magnetic anomaly detection. This paper propose an improved adaptive coherent noise suppression(ACNS) method, which provides an ...effective denoising method for magnetic anomaly detection. Firstly, the signal of three-axis fluxgate sensor and their total magnetic field signal are denoised by the ACNS method, secondly, the four groups of signal above are summed by the adaptive weighted summation method, and then we use OBF algorithm to get the energy of the signal, achieve the goal of magnetic anomaly detection. Finally, the experimental results show that the improved method in this paper has better denoising effect than the original method, and the magnetic anomaly can be detected better by OBF algorithm after using the improved ACNS algorithm.
Internal waves in the ocean environment produce weak magnetic fields through induction as seawater is conductive. The induced field can be detected in measurements of the magnetic field using a ...sensitive magnetometer. Isolating the magnetic signature of these ubiquitous phenomena from geomagnetic and noise sources requires careful analysis. The experiment uses two fixed bottom mounted magnetometers, one on shore and the other underwater, and an underwater bottom mounted acoustic Doppler current profiler (ADCP). Raw signals are adjusted for any data corruption and anthropomorphic interference, such as large spike removal through Anderson functions. Wavelet decomposition is used to automatically detect spikes in the magnetic data and allows for their replacement through interpolation schemes. Then filtering techniques, including frequency-domain cancellation (FDC), are used to show the signature of the internal wave. These results are correlated with ADCP data to search for internal wave activity.
PDF
