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
This paper develops a localization method to estimate the depth of a target in the context of active sonar, at long ranges. The target depth is tactical information for both strategy and classification purposes. The Cramer-Rao lower bounds for the target position as range and depth are derived for a bilinear profile. The influence of sonar parameters on the standard deviations of the target range and depth are studied. A localization method based on ray back-propagation with a probabilistic approach is then investigated. Monte-Carlo simulations applied to a summer Mediterranean sound-speed profile are performed to evaluate the efficiency of the estimator. This method is finally validated on data in an experimental tank.
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
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