Near-field Sources Research Articles

Simplified High-Order DOA and Range Estimation With Linear Antenna Array

In this letter, we propose a new efficient method to estimate the direction-of-arrival (DOA) and range of near-field sources in a decoupled way. First, a non-Hermitian cumulant matrix is constructed, whose eigenvectors associated with zero eigenvalues are used to directly estimate the DOA by using the MUSIC algorithm. Then, the ranges are estimated with the estimated DOA by orthogonalizing the remained eigenvectors. Compared with other modified 2-D MUSIC, the proposed algorithm can greatly reduce the computational complexity by avoiding a 2-D search with only one matrix and one eigenvalue decomposition. Simulation results show the effectiveness of the proposed method.

Correction to Helical Plasmonic Nanostructures as Prototypical Chiral Near-Field Sources

Correction to Helical Plasmonic Nanostructures as Prototypical Chiral Near-Field Sources

Tsunamis on the Russian Pacific coast: history and current situation

The Pacific coast, including the Kamchatka Peninsula, the Kuriles, the Sea of Japan, the Sea of Okhotsk, and the Bering Sea, is the main tsunami-prone area in Russia. The Far East tsunamis are much more frequent, extensive, and devastating than those in the Black, Caspian, Baltic, and White Sea coasts, as well as in major inland lakes of Baikal, Ladoga, etc. The tsunami catalog of the Russian Far East from 1737 to present lists 110 events with mainly near-field and few far-field sources (105 and 5 events, respectively). Most of the catalogued tsunamis (95 cases) were induced by earthquakes, and few events had volcanic (3), landsliding (2), meteorological (3), and unknown (2) triggers. Altogether there were eleven devastating tsunamis for the period of observations, with >10 m heights, two of which were great events in 1737 and 1952, when the waves exceeded 20 m. The wave heights were in the range 2.5-10 m in fifteen hazardous tsunami events and within the tidal range (~1-2 m) in thirteen cases; the other events were small and detectable only instrumentally. Thus, the average recurrence times for tsunamis of different magnitudes in the Russian Pacific coast are 25 years for devastating events and 10-15 years for hazardous tsunamis; small tsunamis occur almost every year, according to statistics for the last sixty years collected at the regional network of tide stations. The topics discussed in the paper concern the completeness and reliability of the Far East catalog; distribution of tsunami events in space and time; correlation between the intensity of tsunami and the magnitude of the causative undersea earthquake; tsunami recurrence; tsunami warning; and long-term hazard assessment and mapping.

Effects of a near-field rigid sphere scatterer on the performance of linear microphone array beamformers.

Beamformers enable a microphone array to capture acoustic signals from a sound source with high signal to noise ratio in a noisy environment, and the linear microphone array is of particular importance, in practice, due to its simplicity and easy implementation. A linear microphone array sometimes is used near some scattering objects, which affect its beamforming performance. This paper develops a numerical model with a linear microphone array near a rigid sphere for both far-field plane wave and near-field sources. The effects of the scatterer on two typical beamformers, i.e., the delay-and-sum beamformer and the superdirective beamformer, are investigated by both simulations and experiments. It is found that the directivity factor of both beamformers improves due to the increased equivalent array aperture when the size of the array is no larger than that of the scatter. With the increase of the array size, the directivity factor tends to deteriorate at high frequencies because of the rising side-lobes. When the array size is significantly larger than that of the scatterer, the scattering has hardly any influence on the beamforming performance.

Near-Field Acoustic Source Localization and Beamforming in Spherical Harmonics Domain

In this paper, we address the issue of near-field source localization using spherical microphone array. The spherical array has been widely used for far-field source localization due to ease of array processing in spherical harmonics domain. Various methods for far-field source localization has been reformulated in spherical harmonics domain. However, near-field source localization that involves joint estimation of range and bearing of the sources has hitherto not been investigated. In this paper, the near-field data model is developed in spherical harmonics domain. In particular, three methods that jointly estimate the range and bearing of multiple sources in the spherical array framework are proposed. Two subspace-based methods called the Spherical Harmonic MUltiple SIgnal Classification (SH-MUSIC) and the Spherical Harmonics MUSIC-Group Delay (SH-MGD) for near-field source localization are first presented. In addition, a method for near-field source localization and beamforming using Spherical Harmonic MVDR (SH-MVDR) is also formulated. Formulation and analysis of Cramer–Rao bound for near-field sources is presented in spherical harmonics domain. Various source localization experiments were conducted on simulated and signal acquired over spherical microphone array in an anechoic chamber. Root-mean-square error and probability of resolution are utilized as measures to evaluate the proposed methods. The significance and practical application of the proposed methods is discussed using experiment on interference suppression. The near-field SH-MVDR beamforming is utilized in this context.

Comparison of Phase-Based 3D Near-Field Source Localization Techniques for UHF RFID.

In this paper, we present multiple techniques for phase-based narrowband backscatter tag localization in three-dimensional space with planar antenna arrays or synthetic apertures. Beamformer and MUSIC localization algorithms, known from near-field source localization and direction-of-arrival estimation, are applied to the 3D backscatter scenario and their performance in terms of localization accuracy is evaluated. We discuss the impact of different transceiver modes known from the literature, which evaluate different send and receive antenna path combinations for a single localization, as in multiple input multiple output (MIMO) systems. Furthermore, we propose a new Singledimensional-MIMO (S-MIMO) transceiver mode, which is especially suited for use with mobile robot systems. Monte-Carlo simulations based on a realistic multipath error model ensure spatial correlation of the simulated signals, and serve to critically appraise the accuracies of the different localization approaches. A synthetic uniform rectangular array created by a robotic arm is used to evaluate selected localization techniques. We use an Ultra High Frequency (UHF) Radiofrequency Identification (RFID) setup to compare measurements with the theory and simulation. The results show how a mean localization accuracy of less than 30 cm can be reached in an indoor environment. Further simulations demonstrate how the distance between aperture and tag affects the localization accuracy and how the size and grid spacing of the rectangular array need to be adapted to improve the localization accuracy down to orders of magnitude in the centimeter range, and to maximize array efficiency in terms of localization accuracy per number of elements.

An Efficient Classification Method of Mixed Sources

A simple but effective classification and localization method is presented to distinguish the near- and far-field sources from mixed sources, and estimate the range parameters of near-field sources. To distinguish the near- and far-field sources, He et al. fall back on the oblique projection technique (OPT), which would yield extra estimation errors. In this paper, we do not resort to any other estimation technique (such as OPT), but make good use of known information, so as to achieve the separation of both near-field sources and far-field sources as well as estimation of range of near-field sources. Therefore, the proposed method obtains higher estimation accuracy than the method of He et al. Simulation and comparison results with the method of He et al. show the performance of the proposed method in this paper.

Range and Direction of Arrival Estimation of Near-Field Sources in Sensor Arrays using Differential Evolution Algorithm

any algorithms have been proposed in recent years for source localization in near field. Some are based on subspace methods and some use evolutionary computing techniques. This article presents the performance of Differential Evolution (DE) algorithm for range and DOA estimation of near field narrow band sources, impinging on a uniform linear array (ULA) of passive sensors. Mean square error (MSE) is used as a fitness function because it requires only a single snapshot to converge and perform better even in negative SNR. The main contribution of this work is to explore the effectiveness of DE without hybridization for uniform linear arrays. The results of DE are compared with the results of Genetic Algorithm (GA). The effectiveness of both the algorithms is tested on the basis of a large number of Monte-Carlo simulations and their statistical analysis. KeywordsEvolution, Direction of Arrival, Evolutionary Computing, Near field, Source Localization.

CRB analysis of planar antenna arrays for optimizing near-field source localization

This paper focuses on the Cramér Rao bound (CRB) of the azimuth, elevation and range with planar arrays for narrowband near-field source localization, using the exact expression of the time delay. Specifically, the aim of this paper is twofold. First, we derive explicit non-matrix closed-form expressions of approximations of these three CRBs. Second, we use these expressions to optimize near-field source localization. For deriving these expressions, we introduce conditions on the array geometry that allow us to decouple the azimuth, elevation and range parameters to a certain order in λ/r (in which λ and r denote the wavelength and the range, respectively). A particular attention is given to the popular array configurations which are the concentric uniform circular-based arrays, cross and square-based centro-symmetric arrays which satisfy these conditions. In order to control directions of arrivals (DOA) ambiguity, we propose a new criterion, which allows us to design non-uniform square [resp., cross]-based centro-symmetric array configurations with improved near-field range estimation capabilities without deteriorating the DOA precisions w.r.t. uniform square [resp., cross]-based arrays. Finally, we specify the accuracy of our proposed approximated CRBs׳expressions and isotropy׳s conditions w.r.t. the range and the number of sensors.

Oil-material fractionation in Gulf deep water horizontal intrusion layer: Field data analysis with chemodynamic fate model for Macondo 252 oil spill

Among the discoveries of the Deepwater Horizon blowout was the so-called “sub-surface plume”; herein termed the “oil-trapping layer”. Hydrocarbons were found positioned at ~1100–1300m with thickness ~100–150m and moving horizontally to the SW in a vertically stratified layer at the junction of the cold abyssal water and the permanent thermocline. This study focuses on its formation process and fate of the hydrocarbons within. The originality of this work to the field is two-fold, first it provides a conceptual framework which places layer origin in the context of a horizontal “intrusion” from the near-field, vertical, blow-out plume and second, it offers a theoretical model for the hydrocarbon chemicals within the horizontal layer as it moves far-afield. The model quantifies the oil-material fractionation process for the soluble and fine particle. The classical Box model, retrofitted with an internal gradient, the “G-Box”, allows an approach that includes turbulent eddy diffusion coupled with droplet rise velocity and reactive decay to produce a simple, explicit, transparent, algebraic model with few parameters for the fate of the individual fractions. Computations show the soluble and smallest liquid droplets moving very slowly vertically through the layer appearing within the trapping layer at low concentration with high persistence. The larger droplets move-through this trapping zone quickly, attain high concentrations, and eventually form the sea surface slick. It impacts the field of oil spill engineering science by providing the conceptual idea and the algorithms for projecting the quantities and fractions of oil-material in a deep water, horizontal marine current being dispersed and moving far afield. In the field of oil spill modeling this work extends the current generation near-field plume source models to the far-field. The theory portrays the layer as an efficient oil-material trap. The model-forecasted concentration profiles for alkanes and aromatics against the available field data support the proposed theory and the resulting model.

Tsunami hazard assessment along the north shore of Hispaniola from far- and near-field Atlantic sources

Since the devastating earthquake of 2010 in Haiti, significant efforts have been devoted to estimating future seismic and tsunami hazard in Hispaniola. In 2013, following a workshop of experts, UNESCO commissioned an initial modeling study to assess tsunami hazard, essentially from seismic sources, along the North shore of Hispaniola (NSOH), which is shared by the Republic of Haiti (RH) and the Dominican Republic (DR). The scope of this study included detailed tsunami inundation mapping for two selected critical sites, Cap Haitien in RH and Puerto Plata in DR. Results of this effort are reported here, and, although still limited in scope, they are within the framework and contribute to the advancement of the UNESCO IOC Tsunami and other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (CARIBE EWS; von Hillebrandt-Andrade in Science 341:966–968, 2013). In similar work done for critical areas of the US east coast (under the auspice of the US National Tsunami Hazard Mitigation Program), the authors have modeled the most extreme far-field tsunami sources in the Atlantic Ocean basin, including: (1) a hypothetical $$M_w$$ 9 seismic event in the Puerto Rico Trench (PRT); (2) a repeat of the historical 1755 $$M_w$$ 9 earthquake in the Azores convergence zone (LSB); and (3) a hypothetical extreme $$450\,\hbox {km}^3$$ flank collapse of the Cumbre Vieja Volcano (CVV) in the Canary Archipelago. Here, tsunami hazard assessment is performed along the NSOH for these three sources, plus two additional near-field coseismic tsunami sources: (1) a $$M_w$$ 8 earthquake in the western segments of the nearshore Septentrional fault (SF), as a repeat of the 1842 event; and (2) a $$M_w$$ 8.7 earthquake occurring in selected segments of the North Hispaniola Thrust Fault (NHTF). Initial tsunami elevations are modeled based on each source’s parameters and propagated with FUNWAVE-TVD (a nonlinear and dispersive long-wave Boussinesq model) in a series of increasingly fine-resolution nested grids (from 1 arc-min to 205 m) using a one-way coupling methodology. For the two selected sites, coastal inundation is computed with TELEMAC (a Nonlinear Shallow Water wave model), in finer-resolution (12–30 m) unstructured nested grids. While for the EC, PRT is a far-field source, for RH and DR, this would be local source as some of the NSOH would be affected within 1 h or is within 200 km of the PRT. This is per definitions of UNESCO IOC. Regional goes from 200 to 1000 km and within 1 and 3 h, and distant is greater than 3 h and more than 1000 km. We find that among the far-field sources CVV causes the largest impact, with up to 20-m runup at the critical sites while PRT, which is a local source for the NSOH, only causes up to 4-m runup due to its directionality; PRT, however, has both a much shorter return period and would impact the NSOH within 30 min of the earthquake. Among near-field sources, the SF event, as could be expected from a strike-slip fault, only causes a small tsunami, but the NHTF event causes up to 12-m runup in the critical sites, with the tsunami arriving within minutes of the earthquake. Hence, the latter event can be considered as the “Probable Maximum Tsunami” (PMT; following, e.g., the US Nuclear Regulatory Commission terminology) for the NSOH. Results of detailed coastal modeling for this PMT can be used to develop maps of vulnerability for the critical sites and prepare for mitigating measures and evacuation; a few examples of such maps are given in the paper. Although a number of earlier studies have dealt with each of the far-field tsunami sources, the modeling of their impact on the NSOH and that of the near-field sources, presented here as part of a comprehensive tsunami hazard assessment study, are novel. Future work should model additional coastal sites and may consider effects of tsunamis generated by near-field submarine mass failures.

A Novel Method for Near-Field Source Localization in Impulsive Noise Environments

The joint estimation of direction of arrival and range for a near-field source in impulsive noise environments remains unaddressed in array signal processing. Inspired by the robustness of phased fractional lower-order moment and the efficiency of generalized estimation of signal parameters via rotational invariance techniques, a novel near-field source localization method is proposed. To reduce the computational complexity, the estimated parameters are determined by the roots of a polynomial rather than searching for the peaks of the spectrum. To characterize its performance, the Cramer---Rao bounds for the estimated parameters of near-field sources in Cauchy noise environments are derived. Compared with existing methods, the proposed method can avoid spectral peak search, loss of array aperture, and parameter pairing. The simulation results demonstrate that the proposed method is superior to existing methods in terms of the probability of resolution and the estimation accuracy, especially in low generalized signal-to-noise ratio and highly impulsive noise environments.

Mixed Near-Field and Far-Field Sources Localization Based on Uniform Linear Array Partition

Based on the polynomial decomposing method and high-order cumulant technique, a novel localization algorithm for the mixed near-field (NF) and far-field (FF) sources is proposed by using a uniform linear array (ULA). First, the ULA is divided into two sub-arrays, with different phase reference points. Three special fourth-order cumulant matrices are designed to eliminate the range parameters of the NF sources in the steering vectors, which only contain the direction of arrival (DOA) information. Second, based on the ESPRIT algorithm, the DOA of each source at the phase reference point is estimated. Third, with the DOA estimation, the type of the sources is classified by computing its coefficient matrix. Finally, the range parameters of NF sources and the DOAs of FF sources are captured. The proposed algorithm does not require any spectral search, which leads to low computational complexity. Moreover, this algorithm avoids the parameter matching procedure. Numerical experiments are conducted to verify the effectiveness of the proposed algorithm.

Dyadic Green’s Functions for Dipole Excitation of Homogenized Metasurfaces

Dyadic Green’s functions for an electric dipole source over an infinite periodic metasurface are obtained using homogenized, nonlocal, anisotropic, generalized sheet-transition conditions. The homogenized Green’s functions can efficiently model near-field point source excitation of typical metasurface structures. The Green’s functions can be decomposed into discrete and continuous spectral components, providing physical insight into the wave dynamics. Several different metasurfaces are considered, and the results are validated by comparison with a full-wave array-scanning method, demonstrating computational efficiency of the proposed homogenized Green’s function approach.

Near‐Field Source Localization Using Spherical Microphone Arrays

A new method is proposed for joint range and bearing (azimuth and elevation) estimation of multiple near-field acoustic sources using observations collected by a spherical microphone array. First, Spherical Fourier transform (SFT) is used to construct the array signal model in the spherical harmonics domain to decouple range and bearing information. Then the relation among the spherical harmonics of three adjacent degrees is exploited to build the recursive relationship of the signal subspace. Using Eigenvalue decomposition (EVD), bearings are estimated based on the eigenvalues and simultaneously the steering matrix can be represented by the signal subspace. Finally, range is estimated using the energy ratios of the elements of the steering matrix in the spherical harmonics domain. The algorithm can avoid parameter pairing and multi-dimensional searching. It has lower computational complexity than that of the Multiple signal classification (MUSIC) method. The performance is evaluated by Monte-Carlo simulations and the estimation root meansquare errors are compared to the corresponding Cramer-Rao bounds (CRBs) and those of MUSIC range estimates, which demonstrate the validity of the proposed algorithm.

Spatial Correlation of Radial Gaussian and Uniform Spherical Volume Near-Field Source Distributions

In this paper, a pair of analytic expressions describing the correlation functions due to spherically symmetric radial Gaussian and uniform volume near-field source position distributions are presented. An approximate spatial correlation function solution for a radial Gaussian source location distribution is derived and compared with the existing numerical methods. An exact solution for a uniform volume source location distribution is also derived and compared with existing numerical methods. The approximate radial Gaussian solution produces a result consistent with numerical methods for compact source location distributions. The uniform volume solution matches the expected behavior. Finally, the spatial correlation functions were used to design spatially robust beamformers for compact microphone arrays. Both of the spatial correlation function solutions lead to improved spatial robustness for the applications of signal enhancement and suppression.

Conceptual hydrodynamic-thermal mapping modelling for coral reefs at south Singapore sea

Coral reefs are important ecosystems that not only provide shelter and breeding ground for many marine species, but can also control of carbon dioxide level in ocean and act as coastal protection mechanism. Reduction of coral reefs at Singapore coastal waters (SCW) region remains as an important study to identify the environmental impact from its busy industrial activities especially at the surrounding of Jurong Island in the south. This kind of study at SCW was often being related to issues such as turbidity, sedimentation, pollutant transport (from industry activities) effects in literatures, but seldom investigated from the thermal change aspect. In this paper, a computational model was constructed using the Delft3D hydrodynamic module to produce wave simulations on sea regions surrounding Singapore Island. The complicated semi-diurnal and diurnal tidal wave events experienced by SCW were simulated for 2 weeks duration and compared to the Admiralty measured data. To simulate the thermal mapping at the south Singapore coastal waters (SSCW) region, we first adapted a conversion of industrial to thermal discharge; then from the discharge affected area a thermal map was further computed to compare with the measured coral map. The outcomes show that the proposed novel thermal modelling approach has quite precisely simulated the coral map at SSCW, with the condition that the near-field thermal sources are considered (with the coverage area in the limit of 20km×20km).

Optical interactions with a charged metallic nanoshell

The effect of extraneous charge on the optical interactions with metallic nanoshells is studied theoretically based on an effective medium model, with the electrodynamic theory also formulated to justify the accuracy of this model. Both optical far-field and near-field interactions will be studied. Furthermore, the hybridization model is generalized to include the charge effects yielding results for the multipole resonances consistent with those from the effective medium model. It is found that while the extraneous charges will lead to blueshifted resonances, their effect on the bonding modes will be most significant, especially for localized near-field sources. In addition, it is pointed out that the applicability of our theory can go beyond the metallic nanoshell to include graphene-coated core–shell particles studied recently in the literature.

A Geometry Calibration Technique for Hydrophone Array with Sources in Near Field

A new algorithm involving flank array geometry calibration under strong multipath conditions is proposed to address the problem of installation errors and the shell deformation. The derived linear mapping relationship between geometric error of sensors and signal eigenvector reduces the calculating difficulty in near calibration mode. By regarding the reflection as coherent visual sources in known position, the compensation strategy of strong multipath matching is put forward. Cramer–Rao bound (CRB) analysis for the calibration mode is employed. Numerical simulations and lake trials verify the efficiency of the proposed algorithm and illustrate the performance improvement under strong multipath conditions.

Localization of mixed far-field and near-field sources under unknown mutual coupling

In this paper, a novel localization algorithm for mixed far-field and near-field sources is proposed in the presence of unknown mutual coupling. Based on the principle of rank reduction, direction-of-arrival (DOA) estimates of far-field sources are firstly decoupled under unknown mutual coupling. Then these estimates are employed to generate the mutual coupling coefficients. Finally, by the mutual coupling compensation and the far-field components elimination, near-field sources parameters (DOA and range) are obtained. The proposed algorithm is efficient in that it only requires second order statistics and one dimensional spectral search. Simulation results demonstrate that our algorithm is effective for the classification and localization of mixed sources under unknown mutual coupling.