Source Localization Accuracy Research Articles

FEM based 3D modelling of partial discharge detection and localization in an oil-filled power transformer using piezoelectric acoustic sensor

Abstract The main cause of insulation degradation is due to partial discharges (PDs) occurring inside the transformer, and its detection and localization are the most effective, non-destructive methods to assess the insulation condition of the transformer. Among the PD detection methods, the acoustic PD detection technique is popular because of its various advantages. The acoustic PD detection method for accurate PD source localization becomes quite challenging when PD occurs inside the transformer core and windings. As the acoustic sound wave can be distorted and vibration with its distribution, so the type of PD sensors with their setting in the transformer should be thoroughly investigated and chosen. In this work, via simulation, the acoustic sound distribution inside the power transformer due to PD occurs is studied. Based on the knowledge of acoustic pressure wave distribution, a Lead Zirconate Titanate (PZT-5H) sensor is designed using Finite element method based COMSOL Multiphysics software and placed it on the outer walls of the transformer for PD detection and localization. The PD induction position has been recognized from the sensor signal using an artificial neural network. The results of PD detection and localization by the proposed piezoelectric sensor and COMSOL probe point are in good agreement.

Pareto‐optimal design of UHF antenna using modified non‐dominated sorting genetic algorithm II

In this study, the ultra-high-frequency (UHF) antenna for partial discharge (PD) detection is optimised to simultaneously satisfy the requirements of low return loss and high fidelity factor (FF) in the frequency band of interest by using the modified non-dominated sorting genetic algorithm II (MNSGA-II). Based on the labour division strategy, the MNSGA-II adopts an adaptive crossover and mutation possibilities instead of the fixed ones, resulting in the significant improvement of convergence rate and exploration ability. One of the Pareto-optimal solutions is presented as the authors’ proposed UHF antenna, whose performance is compared with those of both the antenna optimised by genetic algorithm and the existing wideband antennas. The experimental results show that the proposed antenna with a compact size of 0.201 λ L × 0.198 λ L realises the reflection coefficient less than −10 dB from 490 MHz to 1.52 GHz, and its FFs in the face-to-face and side-by-side scenarios are 0.897 and 0.845, respectively. Furthermore, the simulation results reveal that the high FF of antenna greatly increases the accuracy of PD source localisation. It indicates that the MNSGA-II provides an excellent solution to the multiobjective optimisation problems in antenna design.

Effects of Independent Component Analysis on Magnetoencephalography Source Localization in Pre-surgical Frontal Lobe Epilepsy Patients.

Objective: Magnetoencephalography source imaging (MSI) of interictal epileptiform discharges (IED) is a useful presurgical tool in the evaluation of drug-resistant frontal lobe epilepsy (FLE) patients. Yet, failures in MSI can arise related to artifacts and to interference of background activity. Independent component analysis (ICA) is a popular denoising procedure but its clinical application remains challenging, as the selection of multiple independent components (IC) is controversial, operator dependent, and time consuming. We evaluated whether selecting only one IC of interest based on its similarity with the average IED field improves MSI in FLE.Methods: MSI was performed with the equivalent current dipole (ECD) technique and two distributed magnetic source imaging (dMSI) approaches: minimum norm estimate (MNE) and coherent Maximum Entropy on the Mean (cMEM). MSI accuracy was evaluated under three conditions: (1) ICA of continuous data (Cont_ICA), (2) ICA at the time of IED (IED_ICA), and (3) without ICA (No_ICA). Localization performance was quantitatively measured as actual distance of the source maximum in relation to the focus (Dmin), and spatial dispersion (SD) for dMSI.Results: After ICA, ECD Dmin did not change significantly (p > 0.200). For both dMSI techniques, ICA application worsened the source localization accuracy. We observed a worsening of both MNE Dmin (p < 0.05, consistently) and MNE SD (p < 0.001, consistently) for both ICA approaches. A similar behaviour was observed for cMEM, for which, however, Cont_ICA seemed less detrimental.Conclusion: We demonstrated that a simplified ICA approach selecting one IC of interest in combination with distributed magnetic source imaging can be detrimental. More complex approaches may provide better results but would be rather difficult to apply in real-world clinical setting. In a broader perspective, caution should be taken in applying ICA for source localization of interictal activity. To ensure optimal and useful results, effort should focus on acquiring good quality data, minimizing artifacts, and determining optimal candidacy for MEG, rather than counting on data cleaning techniques.

Efficient Seismic Source Localization Using Simplified Gaussian Beam Time Reversal Imaging

With the dramatic growth of seismic data volume, efficient and accurate seismic source location has become a significant challenge to seismologists. Recently, time reversal imaging (TRI) has been widely applied in automatic seismic source location for its robustness and accuracy, but its wave-equation-based implementation is usually computationally expensive. To achieve an efficient in situ and real-time source location, the emerging sensor network is a good option. In this article, we propose a simplified Gaussian beam TRI (SGTRI) method to implement the seismic source location in a distributed sensor network. Gaussian beam (GB) is a high-frequency asymptotic solution of the wave equation, which can help reduce the computation costs of the wavefield extrapolation in conventional TRI. Traditionally, the GB construction for reflection seismic imaging covers the entire subsurface space. However, for certain source localization, only limited areas contribute. Thus, we propose a beamforming-technique-based simplified GB construction to further boost efficiency. Then, we propose an imaging condition for the SGTRI to construct the final source location map. Using synthetic experiments, we demonstrate the accuracy, robustness, and efficiency of the proposed method compared with conventional TRI. In the end, a field application also shows promising results.

Evaluation of acoustic emission source localization accuracy in concrete structures

Acoustic emission source localization is a promising monitoring technique for concrete structures. However, the accuracy of acoustic emission source localization is influenced by many factors, such as the presence of cracks, which are commonly observed in existing reinforced concrete structures. In this article, the acoustic emission source localization is evaluated using a numerical model with a total number of 11,827,200 independent simulated tests. In this work, the investigated influential factors include the presence of cracks, arrival time picking error, and senor layout. The accuracy of source localization is quantified by the characteristic error defined in this article. Using the proposed wave propagation properties, a relatively stable characteristic error of 150 mm is estimated in the detection zone with the maximum sensor spacing less than 1 m. The evaluation approach and simulated characteristic error are validated experimentally by comparing the 200 manually generated signals using hammer hits on a cracked concrete beam.

Localization of Swept Free-Tip Airfoil Noise Sources by Microphone Array Processing

A postprocessing methodology of microphone-array results for accurate source localization and separation is described. A method constrained iterative restoration algorithm with an assumption of uncorrelated sources is used to extract quantitative spectral results for multiple noise sources identified on a wall-mounted finite-span swept and cambered airfoil tested in an open-jet aeroacoustic facility. This allows understanding of the contribution of each source in the noise generation process. The total sound pressure level is reconstructed from the individual spectra of each noise source and extrapolated in the far field to be compared with a single-microphone spectrum. The Bayesian algorithm is used to improve the comparison between reconstructed and experimental spectra because it takes into account the coherent nature of the sources. The analytical models of the source mechanisms and of their spanwise correlation are proposed as a tool to define future improvements.

Sensitivity maps for time-reverse imaging: an accuracy study for the Los Humeros Geothermal Field (Mexico)

SUMMARY The estimation of the source–location accuracy of microseismic events in reservoirs is of significant importance. Time-reverse imaging (TRI) provides a highly accurate localization scheme to locate events by time-reversing the recorded full wavefield and back propagating it through a velocity model. So far, the influence of the station geometry and the velocity model on the source–location accuracy is not well known. Therefore, sensitivity maps are developed using the geothermal site of Los Humeros in Mexico to evaluate the spatial variability of the source–location accuracy. Sensitivity maps are created with an assumed gradient velocity model with a constant vp–vs ratio and with a realistic velocity model for the region of Los Humeros. The positions of 27 stations deployed in Los Humeros from September 2017 to September 2018 are used as surface receivers. An automatic localization scheme is proposed that does not rely on any a priori information about the sources and thus negates any user bias in the source locations. The sensitivity maps are created by simulating numerous uniformly distributed sources simultaneously and locating these sources using TRI. The found source locations are compared to the initial source locations to estimate the achieved accuracy. The resulting sensitivity maps show that the station geometry introduces complex patterns in the spatial variation of accuracy. Furthermore, the influence of the station geometry on the source–location accuracy is larger than the influence of the velocity model. Finally, a microearthquake recorded at the geothermal site of Los Humeros is located to demonstrate the usability of the derived sensitivity maps. This study stresses the importance of optimizing station networks to enhance the accuracy when locating seismic events using TRI.

Improving the resolution of underwater acoustic image measurement by deconvolution

The conventional beamforming (CBF) map of underwater acoustic image measurement can be expressed as a convolution of the source distribution and the response of the beamformer to a point source, defined as the beam pattern or the point spread function (PSF). By deconvolving the CBF beamformer’s map, the distribution of the actual sources with a clean beam map can be obtained to improve the resolution. In this paper, the deconvolved conventional beamforming (dCv) is applied to underwater acoustic image measurement to improve the accuracy of sound source localization. Due to the point spread function of the array in near field is dependent on the focused point, which means that the PSF is shift variant, so it is necessary to use shift-variant deconvolution method. In this paper, an extended Richardson-Lucy (Ex-RL) algorithm is applied to the two-dimensional shift-variant deconvolution acoustic image measurement problem to improve resolution. The method is compared with the original-RL, classical deconvolution approach for the mapping of acoustic sources (DAMAS) and non-negative least squares (NNLS). The simulation and the experiment results verify the effectiveness of the algorithm.

ESA THESEUS and Czech participation

AbstractThe recent status of the European Space Agency's (ESA) THESEUS (Transient High‐Energy Sources and Early Universe Surveyor) project and the recent and expected Czech participation in this project are briefly presented and discussed. THESEUS is a mission concept proposed in response to the ESA's call for medium‐size mission (M5) within the Cosmic Vision Programme and selected by ESA on May 7, 2018, to enter an assessment phase A/0 study. The expected Czech participation is on the Soft X‐ray Imager (SXI) and a set of four lobster‐eye (LE) telescopes, covering a total field of view (FOV) of 1 sr with source location accuracy better than 1–2 arcmin and energy coverage 0.3–6 keV. We also show the prospects of detecting and observing cataclysmic variables (CVs) with the hard X‐ray imaging spectrometer (XGIS) and SXI. Since the X‐ray spectrum largely determines what emission components and mechanisms can be observed, a combination of these instruments will be very useful. Also if we concentrate on the long‐term activity of CVs, it will even be meaningful to use the observations of CVs located in the wide FOVs of XGIS and SXI when searching for and observing other types of events such as gamma‐ray bursts.

A fusion algorithm of passive sound source localization based on the two-plane four-element cross array

In this work, a fusion algorithm is proposed for improving the accuracy and stability of passive sound source localization. Different from the traditional algorithm that contains a single-plane cross array, here, the fusion algorithm is used to overcome the position blur in the process of localization. First, the two-plane four-element cross array model is established. Based on this model, the method is defined to judge the position where the sound source is located. According to the localization principle, we derive the calculation formula of the sound source position, based on a single four-element planar array. Then, the elevation angle sine value is introduced into the coordinate formula as the weighted coefficient by analyzing the indirect measurement error, and the fusion algorithm is employed to conduct the sound source localization, based on the two-plane four-element cross array. Finally, the relationships are obtained, between the time delay estimation error, the elevation angle, the horizontal angle, and the localization performance. Besides, the validity of this algorithm is validated by measuring the ranging and direction-finding accuracy. The results show that the distance error rate is within 2%, and the angle error rate is within 3%, which means a good localization effect. The proposed algorithm is expected to be widely used in thunderstorm cloud detection for its quick measurement and high precision.

Acoustic Emission Source Location and Experimental Verification for Two-Dimensional Irregular Complex Structure

The location of the acoustic emission (AE) source can monitor the development of the crack in real time in the complex structure. In recent years, numerous location algorithms have been proposed, but the following three problems still affect the accuracy and application of source location. First, the elastic wave velocity is assumed as a fixed value. Second, the geometric irregularities of the structure are not considered. Third, these methods based on data map require a considerable amount of time for repeated training to cover the location area. To solve above issues, we proposed an A* Localization Method without premeasured velocity (ALM), which not only avoids manual repetitive training by searching for paths between equidistant grid nodes and sensors, but also takes advantage of the localization method without requiring pre-measured velocity. Furthermore, the improved A* search algorithm is used to search the fastest wave path in the complex structures with irregular spaces. The ALM is verified by the virtual localization tests and the lead-breaking tests. Results show that the location accuracy was improved significantly by the ALM. It is concluded that the ALM can be available to AE source location for the two-dimensional complex structure with geometric irregularities.

3D Generalized Inverse Beamforming in wind tunnel aeroacoustic testing: application to a Counter Rotating Open Rotor aircraft model

Inverse methods are gaining relevance in the aeroacoustic community for their capability to accurately localize and quantify noise sources. Indeed, since modern aircraft are more targeted to the reduction of fuel consumption, and very often some design choices, like Open Rotor (OR) propulsion systems, cause excessive acoustic emissions, accurate knowledge of noise source locations is of fundamental importance. This paper describes the use of an inverse method, namely Generalized Inverse Beamforming (GIBF), to characterize a Counter Rotating Open Rotor (CROR) installed on a 1/7th scale aircraft model. The model was tested in a large Low-Speed Wind Tunnel (WT) at The Pininfarina Aerodynamic and Aeroacoustic Research Center in Turin, Italy, within the framework of the FP7 EU Clean-Sky WENEMOR (Wind tunnel tests for the Evaluation of the installation effects of Noise EMissions of an Open Rotor advanced regional aircraft) project. With respect to previous works already published, the pros and cons of 3D GIBF formulation will be discussed on data collected from an industrial test case. A comparison of L2 and L1 norm formulations, as well as multiplicative approach and single array processing in 3D GIBF, will be performed, discussing their differences in terms of source localization accuracy. Since a quantitative analysis on real data cannot be provided because of confidentiality issues, the capability of the present approach to correctly quantify the source strength will be evaluated by considering a synthetic monopole source emitting white noise at different signal-to-noise-ratios (SNRs). Finally, it will be shown that 3D GIBF can provide engineers with more reliable data regarding the acoustic behavior of CROR-based aircrafts, this proving the advantages in exploiting this inverse method in WT aeroacoustic applications.

Prompt and accurate sky localization of gravitational-wave sources

Accurate, precise and prompt sky localization of gravitational-wave sources is essential to the success of multi-messenger astronomy. One of the most accurate sky localizations we can obtain is from full signal parameter estimation obtained with the LIGO-Virgo LALInference software, done after a quick initial sky localization with the Bayestar software. While more accurate, the improved analysis can take on the order of months to complete for a binary neutron star event. To solve this issue, we develop a new technique to speed up the parameter estimation. Our technique speeds up the parameter estimation by a factor of (104) and enables updating the sky localization within 10 minutes after the detection.

Free-Field TDOA-AOA Sound Source Localization Using Three Soundfield Microphones

Accurate source localization is an important problem in many research areas as well as practical applications in wireless communications and acoustic signal processing. This paper presents a passive three-dimensional sound source localization (SSL) method that employs a geometric configuration of three soundfield microphones. Two methods for estimating the angle of arrival (AOA) and time difference of arrival (TDOA) are proposed based on Ambisonics A and B format signals. The closed-form solution for sound source location estimation based on two TDOAs and three AOAs is derived. The proposed method is evaluated by simulations and physical experiments in our anechoic chamber. Simulations demonstrate that the estimation method can theoretically obtain Cramer-Rao lower bound for a small Gaussian noise present in AOA and TDOA observations. Investigation on the uncertainty of TDOA and AOA measurements depending on the length of measurement interval is also conducted. Experimental results in terms of RMSE indicate that the proposed solution can be used to accurately find a 3D position of the sound source in free-field environment. Performance evaluation regarding the number of estimation steps shows that higher accuracy can be achieved by longer observations of stationary sound source.

Effective Acoustic Energy Sensing Exploitation for Target Sources Localization in Urban Acoustic Scenes

This letter proposes a new approach to improve the accuracy of the energy-based source localization methods in urban acoustic scenes. The proposed acoustic energy sensing flow estimation (ESFE) uses the sensors signal nonstationarity degree to determine the area with highest energy concentration in the scenes. The ESFE is applied to different acoustic scenes and yields to source localization accuracy improvement with computational complexity reduction. The experiments results show that the proposed scheme leads to significant improvement in source localization accuracy.

Efficient Localization Algorithm for Near-Field Noncircular Sources via Dual-Polarization Sensor Array

Noncircular signals are widely used in the area of radar, sonar, and wireless communication array systems, which can offer more accurate estimates and detect more sources. In this paper, the noncircular signals are employed to improve source localization accuracy and identifiability. Firstly, an extended real-valued covariance matrix is constructed to transform complex-valued computation into real-valued computation. Based on the property of noncircular signals and symmetric uniform linear array (SULA) which consist of dual-polarization sensors, the array steering vectors can be separated into the source position parameters and the nuisance parameter. Therefore, the rank reduction (RARE) estimators are adopted to estimate the source localization parameters in sequence. By utilizing polarization information of sources and real-valued computation, the maximum number of resolvable sources, estimation accuracy, and resolution can be improved. Numerical simulations demonstrate that the proposed method outperforms the existing methods in both resolution and estimation accuracy.

Accuracy of source localization for eccentric inspiraling binary mergers using a ground-based detector network

The problem of gravitational wave parameter estimation and source localization is crucial in gravitational wave astronomy. Gravitational waves emitted by compact binary coalescences in the sensitivity band of second-generation ground-based detectors could have non-negligible eccentricities. Thus it is an interesting topic to study how the eccentricity of a binary source affects and improves the accuracy of its localization (and the signal-to-noise ratio). In this work we continue to investigate this effect with the enhanced postcircular waveform model. Using the Fisher information matrix method, we determine the accuracy of source localization with three ground-based detector networks. As expected, the accuracy of source localization is improved considerably with more detectors in a network. We find that the accuracy also increases significantly by increasing the eccentricity for the large total mass ($M\ge 40M_\odot$) binaries with all three networks. For the small total mass ($M<40 M_\odot$) binaries, this effect is negligible. For the smaller total mass ($M<5 M_\odot$) binaries, the accuracy could be even worse at some orientations with increasing eccentricity. This phenomenon comes mainly from how well the frequency of the higher harmonic modes induced by increasing eccentricity coincides with the sensitive bandwidth of the detectors. For the case of the $100 M_\odot$ black hole binary, the improvement factor is about $2$ in general when the eccentricity grows from $0.0$ to $0.4$. For the cases of the $22 M_\odot$ black hole binary and the $2.74 M_\odot$ neutron star binary, the improvement factor is less than $1.1$, and it may be less than 1 at some orientations.

Gas source localization accuracy: A comparison between conventional, weighted arithmetic mean and kernel-based gas distribution mapping methods in small indoor area

This work focuses on comparing gas source localization accuracy of three types of gas source localization methods which are the conventional method, weighted-averaging mean method and variance map from DM+V method. Gas source localization accuracy in this work means the distance error between the calculated source location and the actual source location. All methods were implemented offline using the measurements collected from real-time gas source localization experiments that were done beforehand. The dataset consists of gas sensor measurements, and mobile robot’s location in a 3m by 6m test area. The goal of the work is to shine a light on why recent works in the field are more focusing on improving probabilistic and map-based algorithms. This work also shows how the kernel size of kernel-based gas distribution mapping might affect the gas source localization accuracy in a small indoor area.

Comparative Study on Power Oscillation Disturbance Source Location Method Based on Oscillation Energy Flow

With the rapid development of the wide area measurement system (WAMS), the disturbance source location method based on oscillation energy has been widely used in low frequency oscillation monitoring. This paper focuses on the applicability research of different oscillation energy methods. Taking the forced power oscillation caused by the excitation system abnormality as an example, the disturbance source location accuracy of three oscillation energy methods is compared. The results show that it is important to extract the dominant component of the electrical signal. When the non-dominant component content is large, it will affect the location accuracy of the traditional oscillation energy method.

Arbitrary Microphone Array Optimization Method Based on TDOA for Specific Localization Scenarios.

Various microphone array geometries (e.g., linear, circular, square, cubic, spherical, etc.) have been used to improve the positioning accuracy of sound source localization. However, whether these array structures are optimal for various specific localization scenarios is still a subject of debate. This paper addresses a microphone array optimization method for sound source localization based on TDOA (time difference of arrival). The geometric structure of the microphone array is established in parametric form. A triangulation method with TDOA was used to build the spatial sound source location model, which consists of a group of nonlinear multivariate equations. Through reasonable transformation, the nonlinear multivariate equations can be converted to a group of linear equations that can be approximately solved by the weighted least square method. Then, an optimization model based on particle swarm optimization (PSO) algorithm was constructed to optimize the geometric parameters of the microphone array under different localization scenarios combined with the spatial sound source localization model. In the optimization model, a reasonable fitness evaluation function is established which can comprehensively consider the positioning accuracy and robustness of the microphone array. In order to verify the array optimization method, two specific localization scenarios and two array optimization strategies for each localization scenario were constructed. The optimal array structure parameters were obtained through numerical iteration simulation. The localization performance of the optimal array structures obtained by the method proposed in this paper was compared with the optimal structures proposed in the literature as well as with random array structures. The simulation results show that the optimized array structure gave better positioning accuracy and robustness under both specific localization scenarios. The optimization model proposed could solve the problem of array geometric structure design based on TDOA and could achieve the customization of microphone array structures under different specific localization scenarios.