IMPROVED BEAMFORMER WITH WEIGHTED SOURCE REGION SUPPRESSION FOR COHERENT MEG SOURCE LOCALIZATION

2010 ◽  
Vol 22 (03) ◽  
pp. 239-248 ◽  
Author(s):  
Junpeng Zhang ◽  
Dezhong Yao
Keyword(s):  
Source Region ◽  
Minimum Variance ◽  
Imaging Method ◽  
Performance Simulation ◽  
Coherent Sources ◽  
Localization Performance ◽  
Spatio Temporal ◽  
Auditory Cortices ◽  
Highly Correlated ◽  
Suppression Region

Beamformer is one of the main techniques for spatio-temporal neuroelectromagnetic source reconstruction. However, the classical Beamformer is extremely sensitive to strongly coherent sources, thereby encountering difficulty in localizing the highly correlated bilateral auditory cortices in auditory evoked field (AEF) or auditory steady state evoked potential. The multiple constrained minimum-variance Beamformer with coherent source region suppression (Beamformer-CS) can potentially overcome such difficulties. However, when coherent interferer is located close to the edges of the suppression region, Beamformer-CS has localization bias and the closer it is, the larger it will be. Here, we present an improved Beamformer-CS that can localize coherent sources with much less localization bias, especially in the case of the interferer close to the edges of the suppression region. First, based on approximate information about source energy distribution from other neuroimaging techniques, a region encompassing the coherent interfering sources is defined. Then, the dominant eigenvectors of the lead field matrix, weighted using source energy information obtained by other imaging method, for the suppression region is incorporated into Beamformer design as hard null constraints. Such weighting strategy is able to improve the localization performance. Simulation test shows that, compared to Beamformer-CS, the new weighting approach is of much smaller localization bias, sharper peak of the estimated sources, more robust against noise, and less sensitiveness to the number of the eigenvector components for the suppression region, as is also confirmed by real AEF data test.

COHERENT MEG/EEG SOURCE LOCALIZATION IN TRANSFORMED DATA SPACE

2010 ◽  
Vol 22 (05) ◽  
pp. 351-365 ◽  
Author(s):  
Junpeng Zhang ◽  
Sarang S. Dalal ◽  
Srikantan S. Nagarajan ◽  
Dezhong Yao
Keyword(s):  
A Priori ◽  
Measurement Data ◽  
Brain Regions ◽  
Imaging Method ◽  
Data Space ◽  
Source Regions ◽  
Neural Activities ◽  
Coherent Sources ◽  
Spatio Temporal ◽  
Auditory Cortices

In some cases, different brain regions give rise to strongly-coherent electrical neural activities. For example, pure tone evoked activations of the bilateral auditory cortices exhibit strong coherence. Conventional 2nd order statistics-based spatio-temporal algorithms, such as MUSIC (MUltiple SIgnal Classification) and beamforming encounter difficulties in localizing such activities. In this paper, we proposed a novel solution for this case. The key idea is to map the measurement data into a new data space through a transformation prior to the localization. The orthogonal complement of the lead field matrix for the region to be suppressed is generated as the transformation matrix. Using a priori knowledge or another independent imaging method, such as sLORETA (standard LOw REsolution brain electromagnetic TomogrAphy), the coherent source regions can be primarily identified. And then, in the transformed data space a conventional spatio-temporal method, such as MUSIC, can be used to accomplish the localization of the remaining coherent sources. Repeatedly applying the method will achieve localization of all the coherent sources. The algorithm was validated by simulation experiments as well as by the reconstructions of real bilateral auditory cortical coherent activities.

Measurement and analysis of species distribution in laser-induced ablation plasma of an aluminum-magnesium alloy

2021 ◽  
Author(s):  
Junxiao Wang ◽  
Shuqing Wang ◽  
Lei Zhang ◽  
Maogen Su ◽  
Duixiong Sun ◽  
...  
Keyword(s):  
Species Distribution ◽  
Laser Energy ◽  
Integral Intensity ◽  
Spectral Lines ◽  
Imaging Method ◽  
Measurement And Analysis ◽  
Ablation Plasma ◽  
Spatio Temporal ◽  
Differential Imaging

Abstract We proposed a theoretical spatio-temporal imaging method, which was based on the thermal model of laser ablation and the two-dimensional axisymmetric multi-species hydrodynamics model. By using the intensity formula, the integral intensity of spectral lines could be calculated and the corresponding images of intensity distribution could be drawn. Through further image processing such as normalization, determination of minimum intensity, combination and color filtering, a relatively clear species distribution image in the plasma could be obtained. Using the above method, we simulated the plasma ablated from Al-Mg alloy by different laser energies under 1 atm argon, and obtained the theoretical spatio-temporal distributions of Mg I, Mg II, Al I, Al II and Ar I species, which are almost consistent with the experimental results by differential imaging. Compared with the experimental decay time constants, the consistency is higher at low laser energy, indicating that our theoretical model is more suitable for the plasma dominated by laser-supported combustion wave.

USTC-MUSIC Algorithm for DOA Estimation of Coherent Sources Using Single Vector Hydrophone

2014 ◽  
Vol 530-531 ◽  
pp. 530-533
Author(s):  
Jin Fang Cheng ◽  
Chao Ran Zhang ◽  
Wei Zhang
Keyword(s):  
Correlation Matrix ◽  
Temporal Correlation ◽  
Doa Estimation ◽  
Spatial Smoothing ◽  
Music Algorithm ◽  
Correlation Matrices ◽  
Vector Hydrophone ◽  
Coherent Sources ◽  
Simulation Results ◽  
Spatio Temporal

The MUSIC algorithm cannot deal with the problem of DOA estimation of coherent sources, this paper proposes the USTC (unitary spatio-temporal correlation matrices)-MUSIC algorithm using single vector hydrophone to solve this problem, by utilizing the unitary spatio-temporal correlation matrix instead of the covariance matrix. The simulation results demonstrate that the USTC-MUSIC algorithm has a better ability to distinguish the coherent sources from different directions than the spatial smoothing MUSIC algorithm.

scholarly journals Statistical analysis of the long-range transport of the 2015 Calbuco volcanic eruption from ground-based and space-borne observations

2019 ◽  
Author(s):  
Nelson Bègue ◽  
Lerato Shikwambana ◽  
Hassan Bencherif ◽  
Juan Pallota ◽  
Venkataraman Sivakumar ◽  
...  
Keyword(s):  
Optical Properties ◽  
South America ◽  
South African ◽  
Numerical Models ◽  
Source Region ◽  
Volcanic Plume ◽  
Back Trajectory ◽  
The South ◽  
African Region ◽  
Spatio Temporal

Abstract. This study investigates the influence of the 2015 Calbuco eruption (41.2° S, 72.4° W; Chile) on the total columnar aerosol optical properties over the Southern Hemisphere. The well-known technic of sunphotometry was applied for investigation of the transport and the spatio-temporal evolution of the optical properties of the volcanic plume. The CIMEL sunphotometer measurements performed at 6 South American and 3 African sites were statistically analyzed. This study involves the use of the satellite observations and a back-trajectory model. The passage of the Calbuco plume is statistically detectable on the aerosol optical depth (AOD) observations obtained from sunphotometers and MODIS. This statistical detection confirms that the majority of the plume was transported over the northeastern parts of South America and reached the South African region one week following the eruption. The plume has impacted to a lesser extent the southern parts of South America. The highest AOD anomalies were observed over the northeastern parts of the South America. Over the South African sites, the AOD anomalies induced by the spread of the plume were quite homogeneously distributed between the east and west coast. The optical characteristics of the plume near source region was consistent with a bearing-ash plume. Conversely, the remote sites to the Calbuco volcano were influenced by ash-free plume. The optical properties discuss on this paper will be used as inputs for numerical models for further investigation on the ageing of the Calbuco plume in a forthcoming study.

scholarly journals DOA Estimation for Mixed Uncorrelated and Coherent Sources in Multipath Environment

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Heping Shi ◽  
Wen Leng ◽  
Anguo Wang ◽  
Tongfeng Guo
Keyword(s):  
Linear Array ◽  
Estimation Method ◽  
Doa Estimation ◽  
Spatial Smoothing ◽  
Uniform Linear Array ◽  
Performance Simulation ◽  
Coherent Sources ◽  
Multipath Environment ◽  
Simulation Results ◽  
Effectiveness And Efficiency

A novel direction-of-arrival (DOA) estimation method is proposed to cope with the scenario where a number of uncorrelated and coherent narrowband sources simultaneously impinge on the far-field of a uniform linear array (ULA). In the proposed method, the DOAs of uncorrelated sources are firstly estimated by utilizing the property of the moduli of eigenvalues of the DOA matrix. Afterwards, the contributions of uncorrelated sources and the interference of noise are eliminated completely by exploiting the improved spatial differencing technique and only the coherent components remain in the spatial differencing matrix. Finally, the remaining coherent sources can be resolved by performing the improved spatial smoothing scheme on the spatial differencing matrix. The presented method can resolve more number of sources than that of the array elements and distinguish the uncorrelated and coherent sources that come from the same direction as well as improving the estimation performance. Simulation results demonstrate the effectiveness and efficiency of the proposed method.

scholarly journals A Novel Method to Identify the Physical Mechanism and Source Region of ELF/VLF Waves Generated by Beat-Wave Modulation Using Preheating Technique

Universe ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 43
Author(s):  
Zhe Guo ◽  
Hanxian Fang ◽  
Farideh Honary
Keyword(s):  
Physical Mechanism ◽  
Source Region ◽  
Low Frequency ◽  
Ionospheric Heating ◽  
F Region ◽  
D Region ◽  
Novel Method ◽  
Spatio Temporal ◽  
High Frequency Waves ◽  
Vlf Waves

One of the most important effects of ionospheric heating by HF (high-frequency) waves is the generation of ELF/VLF (extremely low-frequency/very low-frequency) waves by modulated heating. An important limitation of amplitude modulation (AM) is its dependence on ionospheric electrojet, which means to achieve better modulation effect, some strict spatio-temporal conditions must be met. To solve this problem, some possible methods have been proposed including beat-wave (BW) modulation. However, due to the controversy of its mechanism and the source region of the stimulated ELF/VLF waves, it is not clear whether it is an electrojet-independent method or not, which has become one of the hot topics in recent years. In this paper, we found that the effect of preheating on modulation efficiency of BW based on different theories is the opposite. We suppose the opposite character of the influence and effect on the efficiency of BW in D region and F region as a base for a novel method to identify the physical mechanism and source region of BW. This method can be feasible to solve the controversy of BW. The feasibility of this method is verified by simulation results in the paper.

scholarly journals Searching for electromagnetic counterparts to gravitational-wave merger events with the prototype Gravitational-Wave Optical Transient Observer (GOTO-4)

2020 ◽  
Vol 497 (1) ◽  
pp. 726-738 ◽  
Author(s):  
B P Gompertz ◽  
R Cutter ◽  
D Steeghs ◽  
D K Galloway ◽  
J Lyman ◽  
...  
Keyword(s):  
Gravitational Wave ◽  
Gamma Ray ◽  
Source Region ◽  
Binary Neutron Star ◽  
La Palma ◽  
Binary Black Hole ◽  
Test Models ◽  
Localization Performance ◽  
Optical Transient

ABSTRACT We report the results of optical follow-up observations of 29 gravitational-wave (GW) triggers during the first half of the LIGO–Virgo Collaboration (LVC) O3 run with the Gravitational-wave Optical Transient Observer (GOTO) in its prototype 4-telescope configuration (GOTO-4). While no viable electromagnetic (EM) counterpart candidate was identified, we estimate our 3D (volumetric) coverage using test light curves of on- and off-axis gamma-ray bursts and kilonovae. In cases where the source region was observable immediately, GOTO-4 was able to respond to a GW alert in less than a minute. The average time of first observation was 8.79 h after receiving an alert (9.90 h after trigger). A mean of 732.3 square degrees were tiled per event, representing on average 45.3 per cent of the LVC probability map, or 70.3 per cent of the observable probability. This coverage will further improve as the facility scales up alongside the localization performance of the evolving GW detector network. Even in its 4-telescope prototype configuration, GOTO is capable of detecting AT2017gfo-like kilonovae beyond 200 Mpc in favourable observing conditions. We cannot currently place meaningful EM limits on the population of distant ($\hat{D}_L = 1.3$ Gpc) binary black hole mergers because our test models are too faint to recover at this distance. However, as GOTO is upgraded towards its full 32-telescope, 2 node (La Palma & Australia) configuration, it is expected to be sufficiently sensitive to cover the predicted O4 binary neutron star merger volume, and will be able to respond to both northern and southern triggers.

scholarly journals Near-Surface Geological Structure Seismic Wave Imaging Using the Minimum Variance Spatial Smoothing Beamforming Method

2021 ◽  
Vol 11 (22) ◽  
pp. 10827
Author(s):  
Ming Peng ◽  
Dengyi Wang ◽  
Liu Liu ◽  
Chengcheng Liu ◽  
Zhenming Shi ◽  
...  
Keyword(s):  
Seismic Imaging ◽  
Complex Structure ◽  
Minimum Variance ◽  
Imaging Method ◽  
Spatial Smoothing ◽  
Underground Structures ◽  
Reverse Time ◽  
Near Surface ◽  
Imaging Quality ◽  
Time Migration

Erecting underground structures in regions with unidentified weak layers, cavities, and faults is highly dangerous and potentially disastrous. An efficient and accurate near-surface exploration method is thus of great significance for guiding construction. In near-surface detection, imaging methods suffer from artifacts that the complex structure caused and a lack of efficiency. In order to realize a rapid, accurate, robust near-surface seismic imaging, a minimum variance spatial smoothing (MVSS) beamforming method is proposed for the seismic detection and imaging of underground geological structures under a homogeneous assumption. Algorithms such as minimum variance (MV) and spatial smoothing (SS), the coherence factor (CF) matrix, and the diagonal loading (DL) methods were used to improve imaging quality. Furthermore, it was found that a signal advance correction helped improve the focusing effect in near-surface situations. The feasibility and imaging quality of MVSS beamforming are verified in cave models, layer models, and cave-layer models by numerical simulations, confirming that the MVSS beamforming method can be adapted for seismic imaging. The performance of MVSS beamforming is evaluated in the comparison with Kirchhoff migration, the DAS beamforming method, and reverse time migration. MVSS beamforming has a high computational efficiency and a higher imaging resolution. MVSS beamforming also significantly suppresses the unnecessary components in seismic signals such as S-waves, surface waves, and white noise. Moreover, compared with basic delay and sum (DAS) beamforming, MVSS beamforming has a higher vertical resolution and adaptively suppresses interferences. The results show that the MVSS beamforming imaging method might be helpful for detecting near-surface underground structures and for guiding engineering construction.

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