Single Source Zone Research Articles

Multisource localization based on angle distribution of time–frequency points using an FOA microphone

AbstractMultisource localization occupies an important position in the field of acoustic signal processing and is widely applied in scenarios, such as human‐machine interaction and spatial acoustic parameter acquisition. The direction‐of‐arrival (DOA) of a sound source is convenient to render spatial sound in the audio metaverse. A multisource localization method in a reverberation environment is proposed based on the angle distribution of time–frequency (TF) points using a first‐order ambisonics (FOA) microphone. The method is implemented in three steps. 1) By exploring the angle distribution of TF points, a single‐source zone (SSZ) detection method is proposed by using a standard deviation‐based measure, which reveals the degree of convergence of TF point angles in a zone. 2) To reduce the effect of outliers on localization, an outlier removal method is designed to remove the TF points whose angles are far from the real DOAs, where the median angle of each detected zone is adopted to construct the outlier set. 3) DOA estimates of multiple sources are obtained by postprocessing of the angle histogram. Experimental results in both the simulated and real scenarios verify the effectiveness of the proposed method in a reverberation environment, which also show that the proposed method outperforms reference methods.

Upscaled modeling of complex DNAPL dissolution

A straightforward, upscaled DNAPL mass dissolution model is developed using relatively simple input consisting of characteristic dimensions and saturations of a DNAPL accumulation. Multiple accumulations are aggregated into a single source zone volume. Physically, the dissolution process is a combination of flow through the mass (advective component) and flow around the mass (dispersive component). The contribution of each component is based on initial characteristic length scales and the average initial saturation. Changes over time with the depletion of mass are captured with a changing relative permeability and a power law relationship for the fraction of initial mass remaining. The utility of the upscaled process model is demonstrated with data from three studies: numerical simulation of multiple pools, two-dimensional test cell experiments with mixed architecture and with heterogeneous soil, and a controlled field study of multicomponent DNAPL release and depletion. Use of the model successfully reproduced the observed multistage mass discharge in each study and illuminated the governing processes. The power law exponent was relatively constant for the various conditions and relative permeability changes were integral to the success. The numerical and experimental studies were run to complete mass depletion which the upscaled model matched. The input parameters are minimal and are found in typical DNAPL source zone characterization data.

Multi-source localization by using offset residual weight

Multiple sound source localization is a hot issue of concern in recent years. The Single Source Zone (SSZ) based localization methods achieve good performance due to the detection and utilization of the Time-Frequency (T-F) zone where only one source is dominant. However, some T-F points consisting of components from multiple sources are also included in the detected SSZ sometimes. Once a T-F point in SSZ is contributed by multiple components, this point is defined as an outlier. The existence of outliers within the detected SSZ is usually an unavoidable problem for SSZ-based methods. To solve this problem, a multi-source localization by using offset residual weight is proposed in this paper. In this method, an assumption is developed: the direction estimated by all the T-F points within the detected SSZ has a difference along with the actual direction of sources. But this difference is much smaller than the difference between the directions estimated by the outliers along with the actual source localization. After verifying this assumption experimentally, Point Offset Residual Weight (PORW) and Source Offset Residual Weight (SORW) are proposed to reduce the influence of outliers on the localization results. Then, a composite weight is formed by combining PORW and SORW, which can effectively distinguish the outliers and desired points. After that, the outliers are removed by composite weight. Finally, a statistical histogram of DOA estimation with outliers removed is used for multi-source localization. The objective evaluation of the proposed method is conducted in various simulated environments. The results show that the proposed method achieves a better performance compared with the reference methods in sources localization.

Seismic hazard at a triple plate junction: the state of Chiapas (México)

The state of Chiapas (SE Mexico) conforms a territory of complex tectonics and high seismic activity. The interaction among the Cocos, North American and Caribbean tectonic plates, as well as the active crustal deformation inside Chiapas, determines a variety of seismogenic sources of distinct characteristics and particular strong ground motion attenuation. This situation makes the assessment of seismic hazard in the region a challenging task. In this work, we follow the methodology of probabilistic seismic hazard analysis, starting from the compilation of an earthquake catalogue, and the definition of seismogenic source-zones based on the particular seismotectonics of the region: plate-subduction-related sources (interface and intraslab zones), active crustal deformation zones and the shear zone between the North American and Caribbean plates formed by the Motagua, Polochic and Ixcan faults. The latter source is modelled in two different configurations: one single source-zone and three distinct ones. We select three ground motion prediction equations (GMPEs) recommended for South and Central America, plus two Mexican ones. We combine the GMPEs with the source-zone models in a logic tree scheme and produce hazard maps in terms of peak ground acceleration and spectral acceleration for the 500-, 1000- and 2500-year return periods, as well as uniform hazard spectra for the towns of Tuxtla Gutierrez, Tapachula and San Cristobal. We obtain higher values in comparison with previous seismic hazard studies and particularly much higher than the output of the Prodisis v.2.3 software for seismic design in Mexico. Our results are consistent with those of neighbouring Guatemala obtained in a recent study for Central America.

Multiple-to-single sound source localization by applying single-source bins detection

This paper proposes a novel localization scheme for multiple sound sources that imposes the relaxed sparsity constrains (not all time-frequency coefficients are overlapped) on the source signals. First, a “DOA convergence” assumption is proposed, which means that if most of the time-frequency (T-F) bins in a T-F zone are derived from only one source – defined as single source bins (SSBs), the corresponding direction of arrival (DOA) estimates are relatively concentrated with a heavy density. This assumption is validated through statistical analysis by applying a quantitative measure of convergence. Accordingly, by applying the “DOA convergence” assumption, the detection of SSBs is converted to a clustering problem, K-means clustering and density-based spatial clustering of applications with noise (DBSCAN) algorithms are utilized to complete the task in this paper. The cross distortions (localization error due to the cocktail party phenomenon) in localization caused by multiple simultaneously occurring sources is significantly weakened by conducting DOA estimation among these SSBs, i.e., the multiple source localization is rewritten to a single source one among these SSBs. Moreover, the proposed SSBs detection is applicable to other localization methods and not limited to specific microphone topology. Experimental results demonstrate the localization accuracy of the proposed method outperforms the state-of-the- art localization approaches which are based on single source zone detection. However the proposed method is capable of real-time processing, the accuracy is insufficient in the current system. If non-real time processing is allowed, our method can be realized with higher accuracy than the conventional ones.

Single source bins detection‐based localisation scheme for multiple speech sources

A single source bins (SSBs) detection based multiple source localisation scheme is proposed. This scheme is based on detecting the SSBs in mixture signals that are only derived from one source. Specifically, after proposing a ‘DOA convergence’ assumption, K-means clustering algorithm is used for SSBs detecting. Thus, the multiple source localisation is converted to a single source one among these SSBs. Moreover, the proposed SSBs detection is applicable to other localisation methods and not limited to specific microphone topology. Experimental results demonstrate the localisation accuracy of the proposed method outperforms the localisation approaches which are based on single source zone detection.

Volcanomagnetic anomalies: a review and the computation of the piezomagnetic field expected at Vulcano (Aeolian Islands, Italy)

he volcanic area of Vulcano experienced major unrest, which brought the fumarolic field temperatures from slightly less than 300 °C to ca. 700 °C between 1988-1993. The structure underlying the crater, investigated by drillings and by different geophysical techniques, is relatively well-known. This led us to attempt modelling the magnetic anomaly which could be generated by sudden pressure variations in the magma chamber at shallow depth. The rocks embedding the intrusive rock penetrated by drill-holes to a depth of ca. 2000 m are characterized by high susceptibility, which points to the possibility of obtaining significant magnetic anomalies with acceptably weak pressure pulses. The model for straightforward computing of the anomalous field was drawn accounting for (1) the inferred geometry of the Curie isotherrn, (2) presence of a spherical magma reservoir, 2 km wide and centred at a depth of 3.5 km, overlain by (3) a 0.5 km wide and 1.5 km high cylinder simulating the intrusion first revealed by drillings. The model elements (2) and (3) behave as a single source zone and are assumed to lie beyond the Curie point, the contribution to the piezomagnetic effect being provided by the surrounding medium. Under such conditions, a 10 MPa pressure pulse applied within the sourcezone provides a 4 nT piezomagnetic anomaly, compatible with the amplitude of the anomalies observed at those volcanoes of the world where magnetic surveillance is routinely carried out. The analytical method used for computation of the magnetic field generated by mechanical stress is extensively discussed, and the contribution of piezomagnetism to rapid variations of the magnetic field is compared to other types of magnetic anomalies likely to occur at active volcanoes.

Treatment of Parameter Uncertainty and Variability for a Single Seismic Hazard Map

The inputs to probabilistic seismic hazard studies (seismic source zones, earthquake rates, attenuation functions, etc.) are uncertain, being based on subjective judgments and interpretations of limited data. In the face of this uncertainty, we consider (a) how one might “reasonably” determine the ground-motion levels to show on a single probabilistic seismic hazard map, and (b) the extent to which uncertainty in the calculated levels can be meaningfully represented on such a map. If the “best guess” estimates of the earthquake rate, the Gutenberg-Richter b-value and the maximum magnitude for a single source zone are regarded as uncorrelated and the uncertainty in each parameter can be regarded as symmetric about the estimated value, then the probabilistic ground-motion levels calculated using these best estimates represent both most likely values and also approximate mean values.