Range, velocity and immersion estimation of a moving target in a water-filled tank with an active sonar system

International audience—The knowledge of the impulse response of the propagation channel is required for many underwater applications as communication, sonar detection and localization, marine mammals monitoring, etc. In the context of target classification, this impulse response informs about the relative motion between the source/receiver and the target through the Doppler effect. Knowing the emitted signal, the Doppler compression coefficient of each acoustic path can be estimated with the wideband ambiguity plan [1]–[3]. Warping operator based-filter and wideband ambiguity plan can be used to separate acoustic paths in order to remove interferences and estimate properly the target distance and speed [4]. This paper presents a complementary approach to jointly estimate the distance and speed of the target at a small speed with reasonable resolutions. The investigated sources are Binary Phase Shift Keying (BPSK), 22-Welch-Costas, and Pulse Train Frequency Modulation (PTFM) signal. Sources have a large Time-Bandwidth product (high TB) and provide high resolutions. For this reason, an echo model that takes into account a signal temporal compression (Doppler effect) can be used. A reduced-scale laboratory experiment was conducted to estimate the speed vector and depth of a moving target. Results for speed vectors are compared for the three different sources. A ray back propagation algorithm was used and results show correct estimation of the target depth

Estimation de la vitesse d'une cible en mouvement par une méthode large bande et haute résolution

National audience– La connaissance de la réponse impulsionnelle d'un canal de propagation est nécessaire pour un grand nombre d'applications dans le domaine de l'acoustique sous-marine comme la communication, la localisation et détection sonar, la surveillance des mammifères marins... Cette réponse impulsionnelle nous informe sur les distorsions dues au canal, que subit un signal, et sur les déformations (décalage doppler non maîtrisé) engendrées par le mouvement relatif entre source et récepteur. Dans ce contexte, la connaissance du signal transmis permet d'estimer la vitesse apparente de chaque trajet de propagation à l'aide du plan d'ambiguïté large bande [1][2][3]. On sait qu'un filtrage basé sur les opérateurs de déformation temporelle et de plan d'ambiguïté large bande permet de séparer chaque trajet de façon précise afin de supprimer les interférences et d'estimer correctement la réponse impulsionnelle-avec le retard et le facteur de compression [4]. Dans cette étude, il est proposé une approche complémentaire pour estimer conjointement la vitesse et la distance d'une cible à faible vitesse (faible doppler) avec de bonnes résolutions. Les formes d'ondes émises sont des signaux codés tels que les signaux de Costas, les Binary Phase Shift Keying (BPSK) et les trains d'impulsions modulés linéairement en fréquence (Pulse Train Frequency Modulation, PTFM), dans un contexte haute résolution. Ces formes d'ondes étant larges bandes et ayant un fort produit BT, permettent ainsi d'utiliser un modèle d'écho prenant en compte la compression temporelle du signal dû à l'effet Doppler. Abstract – The knowledge of the impulse response of the propagation channel is required for many underwater applications such communication , sonar localization and detection, and marine mammals monitoring. This impulse response affects the signal and informs about the canal distortions, but also modifications (uncontrolled Doppler effects) caused by the relative motion between source and receiver. Knowing the emitted signal, the radial speed of each acoustic path can be estimated with the wideband ambiguity plan [1][2][3]. With warping operators based-filter and wideband ambiguity plan [4], acoustic paths can be accurately separated in order to remove interferences and estimate properly the impulse response-with the delay and the Doppler compression coefficient. This paper presents a complementary approach to jointly estimate the target distance and speed at low speed (low Doppler) with reasonable resolution. The emitted waveforms are 22-Welch-Costas signal, Binary Phase Shift Keying (BPSK) signal, and Pulse Train Frequency Modulation (PTFM) signal. Context is high resolution because signals have a large time-bandwidth product (high TB). For this reason, an echo model that accounts for a signal temporal compression (Doppler effect) can be used

First demonstration of a 12 DFB fiber laser array on a 100 GHz ITU grid, for underwater acoustic sensing application

International audienceWe report for the first time a multiplexed array of 12 distributed feedback fiber lasers (DFB FLs) on a single optical fiber, separated by only 100 GHz (0.8 nm) in the C-band. These lasers are pumped by a 200 mW laser diode at 1480 nm with no apparent impact on the sensor noise floor despite the fact that the residual reflections from adjacent gratings may be enhanced due to the smaller wavelength separation. Each DFB FL, especially developed for serial multiplexing, exhibits low lasing threshold typically between 1 and 2 mW, low intensity noise and very low frequency noise (less than 30 dB re 1 Hz²/Hz at 1 kHz from optical carrier). From these experimental results, extension to 32 DFB FLs array (on 100 GHz ITU grid) multiplexed on one fiber will be discussed

Effets d'une faible contre-réaction optique sur des lasers à fibre DFB pour applications capteurs

National audienceNous étudions l'effet d'une faible réflection externe sur des lasers à fibre à contre-réaction répartie (DFB FLs). Nous démontrons expérimentalement que la phase optique accumulée sur un aller-retour dans la cavité étendue et la réflectivité associée au miroir externe modifient la puissance de sortie et la fréquence d'émission d'un DFB FL. Comme pour un laser à semiconducteurs (SC) contre-réactionné, à réflectivité externe donnée, l'amplitude des variations est constante pour ces deux paramètres quelle que soit la longueur de la cavité externe

Target-depth estimation in active sonar

International audienceIn active sonar, the objectives are to detect, localize and classify an underwater target. Azimuth and range are often used in anti-submarine warfare to localize targets. The depth may also be used as the key tactical information for strategy purposes or as a good feature for target classification or discrimination. Two dimensional arrays as ank arrays, cylindrical arrays, and hullmounted arrays have access to elevation angles. Even linear towed arrays can give some information about the elevation using the different conical bearings measured when multipath propagation arises. In the context of long ranges and summer Mediterranean sound-speed profile (SSP), this paper presents a new target-depth estimation method, which uses elevation and arrival time measures from one sonar ping in a multipath environment. This method is based on ray back-propagation with a probabilistic approach. This localization algorithm minimizes the mean-squared error of elevation angles at the receiver and arrival times between a model and measures. This method is tested through Monte-Carlo simulations of classic active sonar scenarios and using experimental data from a real reduced-scaled tank. In active sonar, acoustic waves can take the same path on the way back or another path, so ray path combinations can occur. Our localization method discusses also about this ray identification, or how these combined acoustic paths were managed

Phase sensitivity to axial strain of microstrustured optical silica fibers

International audienceWe compare, thanks to a Sagnac interferometer, the phase sensitivity to strain of different microstructured optical silica fibers (MSF) that we design and fabricate. Our results show that when a same elongation is applied to different MSF, the induced phase change is equal or lower than the one obtained for a standard fiber, showing no advantage on this parameter for sensing applications

Brillouin fiber laser using As38Se62 suspended-core chalcogenide fiber

International audienceIn this paper, an all-fiber Brillouin laser ring cavity using a 3-m-long suspended-core chalcogenide As38Se62 fiber is reported for the first time to our knowledge. For a nonresonant ring cavity with no servo-locking, a laser threshold power of 37 mW and an efficiency of 26 % were obtained for a fiber having a core diameter of 5 μm. The linewidth of the Brillouin fiber laser and the pump laser were respectively measured to be below 4 kHz, the resolution of our autocorrelator, and 250 kHz, thus showing the linewidth-narrowing nature of the Brillouin laser. This result paves the way to compact Brillouin lasers with low threshold power and good spectral purity. A full experimental Brillouin characterization is also reported. We measured a Brillouin gain spectrum of 14.2 MHz, a Brillouin gain coefficient of 5.6x10-9 m/W and a Brillouin frequency shift of 7.95 GHz in our fiber

Hierarchical Bayesian of ARMA Models Using Simulated Annealing Algorithm

When the Autoregressive Moving Average (ARMA) model is fitted with real data, the actual value of the model order and the model parameter are often unknown. The goal of this paper is to find an estimator for the model order and the model parameter based on the data. In this paper, the model order identification and model parameter estimation is given in a hierarchical Bayesian framework. In this framework, the model order and model parameter are assumed to have prior distribution, which summarizes all the information available about the process. All the information about the characteristics of the model order and the model parameter are expressed in the posterior distribution. Probability determination of the model order and the model parameter requires the integration of the posterior distribution resulting. It is an operation which is very difficult to be solved analytically. Here the Simuated Annealing Reversible Jump Markov Chain Monte Carlo (MCMC) algorithm was developed to compute the required integration over the posterior distribution simulation. Methods developed are evaluated in simulation studies in a number of set of synthetic data and real data