Male sperm whale acoustic behavior observed from multipaths at a single hydrophone

Sperm whales generate transient sounds (clicks) when foraging. These clicks have been described as echolocation sounds, a result of having measured the source level and the directionality of these signals and having extrapolated results from biosonar tests made on some small odontocetes. The authors propose a passive acoustic technique requiring only one hydrophone to investigate the acoustic behavior of free-ranging sperm whales. They estimate whale pitch angles from the multipath distribution of click energy. They emphasize the close bond between the sperm whale’s physical and acoustic activity, leading to the hypothesis that sperm whales might, like some small odontocetes, control click level and rhythm. An echolocation model estimating the range of the sperm whale’s targets from the interclick interval is computed and tested during different stages of the whale’s dive. Such a hypothesis on the echolocation process would indicate that sperm whales echolocate their prey layer when initiating their dives and follow a methodic technique when foraging

Détection et reconnaissance des signaux stochastiques transitoires (application à l'identification des mammifères marins)

Ce travail de thèse porte sur la détection et la reconnaissance des clics émis par les cachalots (Physeter macrocephalus). Ces signaux sont de très courte durée, non stationnaire, noyé dans un bruit dont les caractéristiques peuvent varier au cours du temps. Nous proposons une approche originale basée sur la méthode de Schur. Le recours à cette technique paramétrique est intéressant pour plusieurs raisons. Premièrement, la mise à jour des coefficients se fait de façon récursive à la présentation d'un nouvel échantillon de l'enregistrement acoustique. En choisissant un facteur d'oubli adaptatif, il est possible de réduire la phase de convergence et de suivre au plus près les variations des signaux. Deuxièmement, nous déduisons, de l'ensemble des coefficients, l'information permettant de caractériser les clics des cachalots. Nous pouvons ainsi les distinguer des clics de dauphins bleus et blancs (Stenella Coeruleoalba). Troisièmement, nous avons comparé notre détecteur à d'autres techniques classiques utilisées en bioacoustique. Et les performances obtenues justifient notre choix, y compris pour des rapports signal-sur-bruit défavorable. Quatrièmement, nous avons montré que la complexité de calcul permet d'envisager des applications temps-réel. Ceci est particulièrement important dans l'objectif d'implanter cette méthode dans des stations d'observations acoustiques des mammifères marins.This PhD work is based on the detection and the recognition of sperm whale (Physeter macrocephalus) clicks. These signals are short, non-stationary, recorded with time-variant noise. We propose an original approach based on the Schur method. We chose this parametric technique for meany reasons. Firstly, the coefficients are recursively updated at the presentation of each new sample of the acoustic recordings. Because f an adaptative forgetting factor, the convergence step is reduced and the method is well adapted to the variations of these signals. Secondly, the Schur coefficients contain information necessary for characterizing the sperm whale clicks. We can also distinguish these clicks from the striped dolphin (Stenella Coeruleoalba) clicks. Thirdly, we compared our detector to other classical techniques used in bioacoustics. The obtained performance justifies our choice, even for signals with a weak signal-to-noise ratio. Fourthly, we showed that the computation complexity is compatible with real-time applications. This is essential in the objective of applying this algorithm on marine mammal observation stations using passive acoustics.PARIS12-Bib. électronique (940280011) / SudocSudocFranceF

Consistent retrieval of land surface radiation products from EO, including traceable uncertainty estimates

Earth observation (EO) land surface products have been demonstrated to provide a constraint on the terrestrial carbon cycle that is complementary to the record of atmospheric carbon dioxide. We present the Joint Research Centre Two-stream Inversion Package (JRC-TIP) for retrieval of variables characterising the state of the vegetation–soil system. The system provides a set of land surface variables that satisfy all requirements for assimilation into the land component of climate and numerical weather prediction models. Being based on a 1-D representation of the radiative transfer within the canopy–soil system, such as those used in the land surface components of advanced global models, the JRC TIP products are not only physically consistent internally, but they also achieve a high degree of consistency with these global models. Furthermore, the products are provided with full uncertainty information. We describe how these uncertainties are derived in a fully traceable manner without any hidden assumptions from the input observations, which are typically broadband white sky albedo products. Our discussion of the product uncertainty ranges, including the uncertainty reduction, highlights the central role of the leaf area index, which describes the density of the canopy. We explain the generation of products aggregated to coarser spatial resolution than that of the native albedo input and describe various approaches to the validation of JRC-TIP products, including the comparison against in situ observations. We present a JRC-TIP processing system that satisfies all operational requirements and explain how it delivers stable climate data records. Since many aspects of JRC-TIP are generic, the package can serve as an example of a state-of-the-art system for retrieval of EO products, and this contribution can help the user to understand advantages and limitations of such products.JRC.D.6-Knowledge for Sustainable Development and Food Securit

Underwater Broadband Source Localization Based on Modal Filtering and Features Extraction

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Underwater Broadband Source Localization Based on Modal Filtering and Features Extraction

Passive source localization is a crucial issue in underwater acoustics. In this paper, we focus on shallow water environment (0 to 400&#8201;m) and broadband Ultra-Low Frequency acoustic sources (1 to 100&#8201;Hz). In this configuration and at a long range, the acoustic propagation can be described by normal mode theory. The propagating signal breaks up into a series of depth-dependent modes. These modes carry information about the source position. Mode excitation factors and mode phases analysis allow, respectively, localization in depth and distance. We propose two different approaches to achieve the localization: multidimensional approach (using a horizontal array of hydrophones) based on frequency-wavenumber transform ( method) and monodimensional approach (using a single hydrophone) based on adapted spectral representation ( method). For both approaches, we propose first complete tools for modal filtering, and then depth and distance estimators. We show that adding mode sign and source spectrum informations improves considerably the localization performance in depth. The reference acoustic field needed for depth localization is simulated with the new realistic propagation modelMoctesuma. The feasibility of both approaches, and , are validated on data simulated in shallow water for different configurations. The performance of localization, in depth and distance, is very satisfactory.</p

Robust Underwater localization for Ultra Low frequency sources in operational context

International audienc