A Noise-Robust Method with Smoothed \ell_1/\ell_2 Regularization for Sparse Moving-Source Mapping

The method described here performs blind deconvolution of the beamforming output in the frequency domain. To provide accurate blind deconvolution, sparsity priors are introduced with a smooth \ell_1/\ell_2 regularization term. As the mean of the noise in the power spectrum domain is dependent on its variance in the time domain, the proposed method includes a variance estimation step, which allows more robust blind deconvolution. Validation of the method on both simulated and real data, and of its performance, are compared with two well-known methods from the literature: the deconvolution approach for the mapping of acoustic sources, and sound density modeling

Possible impacts of the transformation of water infrastructure on productive water uses: The case of the Seokodibeng village in South Africa

Water users’ associations / Water supply / Social participation / Land use / Water use / Villages / History / Domestic water / Irrigation water / Food security / Sanitation / Cost recovery / Project management / Pipes / Water balance / Livestock

Time-angle sensitivity kernels for sound-speed perturbations in a shallow ocean

International audienceAcoustic waves traveling in a shallow-water waveguide produce a set of multiple paths that can be characterized as a geometric approximation by their travel time (TT), direction of arrival (DOA), and direction of departure (DOD). This study introduces the use of the DOA and DOD as additional observables that can be combined to the classical TT to track sound-speed perturbations in an oceanic waveguide. To model the TT, DOA, and DOD variations induced by sound-speed perturbations, the three following steps are used: (1) In the first-order Born approximation, the Fr echet kernel provides a linear link between the signal fluctuations and the sound-speed perturbations; (2) a double-beamforming algorithm is used to transform the signal fluctuations received on two source-receiver arrays in the time, receiver-depth, and source-depth domain into the eigenray equivalent measured in the time, reception-angle and launch angle domain; and finally (3) the TT, DOA, and DOD variations are extracted from the double-beamformed signal variations through a first-order Taylor development. As a result, time-angle sensitivity kernels are defined and used to build a linear relationship between the observable variations and the sound-speed perturbations. This approach is validated with parabolic-equation simulations in a shallow-water ocean context

Time-angle ocean acoustic tomography using sensitivity kernels: The forward problem

International audienceBroadband acoustic signals around 1 kHz propagate through shallow water oceanic waveguides of ~100 m in depth and ~2 km in range as multiple ray-like wavefronts. These acoustic arrivals can be characterized by the following observables: travel-time (TT), direction-of-arrival (DOA) and direction-of-departure (DOD). By applying double-beamforming on the point-to-point signals recorded between two source-receiver arrays, the acoustic contribution of each arrival can be separated from the multi-reverberated data and the TT, DOA and DOD observable variations are accurately measured. This study deals with the use of time-angle sensitivity kernels (TASK) to estimate the observable variations induced by sound speed perturbations in the waveguide. This approach is based on the first order Born approximation and takes into account the finite-frequency effects associated with wave propagation. The robustness the TASK approach is analyzed and compared to numerical parabolic equation simulations involving different sound speed perturbations. For example, parameters such as the perturbation location, the value and shape of the perturbation in the waveguide are modified. The combination of several perturbations and the influence of the source-receiver array apertures on the TT, DOA and DOD estimates are also studied

Direction-of-arrival, direction-of-departure and travel-time sensivity kernels obtained through double beamforming in shallow water

International audienceIn an oceanic waveguide, local sound speed variations induce acoustic path changes (angles, amplitudes, delays, etc...). Using vertical arrays in emission and reception and double beamforming, it is possible, for each path, to jointly track these changes in term of travel-time (τ), reception angle (θr) and emission angle (θe). In order to perform ocean acoustic tomography using these observables, we build sensitivity kernels which link the variations of these observables, measured after double beamforming, to sound speed variations. The construction of these kernels is made in two steps. A first order Born approximation of the Green's function is firstly used to derive the Helmholtz equation and obtain the link between the variations of the sound speed distribution and the variations of the received signal. Then, a first order Taylor development in the (t,θr,θe) signal space leads to a linear relation between the variations of the received signal and the variations of the measured travel-time, eception angle and emission angle of each acoustic path after double beamforming. This paper establishes the mathematical expression of sensitivity kernels and results obtained with synthetic data are shown and discussed

UNRAVELING PARENTS' PERCEPTIONS OF ENGLISH LANGUAGE LEARNING

Purpose of the study: This research aims to analyze parents’ perceptions towards the learning of English and the ways they help their children deal with English and language assessment. Methodology: This qualitative study addresses 74 Chilean parents’ perceptions of English teaching and learning. A semi-structured interview was conducted to capture the participants’ perceptions. The data were categorized using content and frequency analysis and the principles of metaphoric analysis. Main findings: The findings suggest that parents hold a positive perception of the English language and believe it is useful for their children’s lives even though they might find the learning of the language difficult. Social implications/Originality: Participants can produce metaphors that regard English as an ability and metaphors that focus on the process of learning the language. The findings of this research are useful for university stakeholders, teachers, preservice teachers, and students. Novelty/Originality of this study: In this study parents, stakeholders who have usually left aside from the language teaching and learning process, are interviewed to unfold their perceptions of what they see and believe when their children learn English

Représentations Temps-Fréquence de la classe de puissance basées sur l'invariant océanique

National audienceEn acoustique sous marine Ultra Basse Fréquence (UBF < 200 Hz), un environnement océanique petit fond (D < 200 m) se comporte comme un guide d'onde dispersif, dans lequel de nombreuses applications (inversion géoacoustique, localisation de source) considèrent la propagation de sources impulsionnelles (canons à air, explosions, baleines, ...). Comment obtenir une représentation temps-fréquence correcte des signaux correspondants? Ces signaux sont multicomposantes, chaque composante possède un retard de groupe non-linéaire et il n'existe pas de lien direct entre les différentes composantes. Cependant, le retard de groupe de chaque composante peut être approximé par une fonction puissance en f puissance (−1/Beta) , où "Beta"est l'invariant océanique (un scalaire qui résume la dispersion globale dans le guide d'onde). On peut alors définir une Beta-classe de représentations temps-fréquence adaptées au signal reçu. La méthode est appliquée avec succès sur des données réelles marines et permet une bonne représentation temps-fréquence des signaux considérés. Elle est robuste au bruit naturel de l'environnement marin, et à une erreur dans le choix de "Beta