HomeChair: P.C. Ching, The Chinese University of Hong Kong, Hong Kong
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Nicole Gache, CPE Lyon (France)
Patrick Chevret, CPE Lyon (France)
Veronique Zimpfer, CPE Lyon (France)
This paper presents a method for target recognition and classification in shallow water environment. It is based on time-frequency filtering matched to a free field reference target response. The decision strategy lies on the comparison of the reference and the filter output signal. The method is applied to an experimental data base containing target acoustic responses measured in a tank for typical configurations (free field, semi-infinite space and waveguide). First, the recognition of a spherical shell is carried out. The obtained rate of recognition and confusion are more than encouraging. Then, a classification procedure is conducted and a degradation of the mean performances is to be noted in the more general case. However, the classification of 3D targets independently of their attitude gives quite satisfactory results.
ic981583.pdf (From Postscript)
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Jianfeng Chen, Northwestern Polytechnical University (China)
Jianguo Huang, Northwestern Polytechnical University (China)
In this paper an underwater high-resolution array processing system is described and most of error factors in experiment are analyzed. A novel and practical approach to array calibration is also presented to alleviatethe effect of these errors. It is different from other algorithms in that array manifold used in subspace-based methods is obtained through automatical measurement instead of using theoretical value. It can efficiently calibrate errors of gain, phase, mutual-coupling, location, and other reasons generated by the array and sensors even they are direction dependent. Spatial smoothing technique is employed and so the method is effective no matter the sources are correlated or uncorrelated. It is also proved by the test that spatial smoothing is beneficial to reduce some kinds of error. At last, several experimental results are provided to verify the efficiency of the new method.
ic981136.pdf (From Postscript) TOP
Brian F Harrison, Naval Undersea Warfare Center (U.S.A.)
Janet L Harrison, Naval Undersea Warfare Center (U.S.A.)
An optimal approach to matched-field source localization in the presence of environmental uncertainties is the maximum a posteriori (MAP) estimator. The MAP estimator can be interpreted as an exponentially-weighted average over environmental realizations. In practice, only a finite number of environmental realizations can be included in this average resulting in a suboptimal processor. In this paper, we propose an Lp-norm estimator as a robust alternative to MAP in the presence of finite environmental sampling. We also show, using wavenumber gradients, that accurate localization estimates can be obtained using environmental realizations besides the precise true. Simulation results from a shallow-water environment are presented to illustrate the performance improvement.
ic981225.pdf (From Postscript) TOP
Anton J Haug, The MITRE Corporation (U.S.A.)
Gary M Jacyna, The MITRE Corporation (U.S.A.)
The Range Focused Beamformer (RFB) and the Triple Aperture Crosscorrelator (TAC) are the two primary wavefront curvature ranging techniques used in fielded sonar systems. Theoretical performance bounds have been presented in the past for both approaches. This paper develops unified array processing performance bounds where the RFB and the TAC are special cases. Specifically, general Cramer-Rao Lower Bounds (CRLB) on range and bearing estimation for a linear array of directional elements are developed, where the CRLB for the RFB and the TAC are shown to be special cases of the general theory. The ranging performance of the two techniques are then compared.
ic981051.pdf (From Postscript) TOPJohn M Bourdelais, GTE (U.S.A.)
An adaptive beamforming algorithm was developed for broadband active sonar with a convergence time on the order of the pulse duration and effective interference nulling capabilities which enhance desirable echoes. The algorithm is an element based time domain implementation in which beam data that is formed in the direction of each interferer is successively subtracted from the element data using an adaptive FIR filter. The algorithm was applied to impulsive source sonar data received on a bottomed hydrophone array. Collected data contained interfering active returns and noise from nearby shipping as well as desirable echoes from passive reflectors placed near the array. In a representative example, the algorithm adapted fast enough to null out active interference as well as shipping noise, which enhanced the signal to noise ratio of a passive reflector echo by 6 dB.
ic981840.pdf (From Postscript) TOP
Tetsuya Kawase, Keio University (Japan)
Hideshi Tsurunosono, Keio University (Japan)
Naoki Ehara, Keio University (Japan)
Iwao Sasase, Keio University (Japan)
Maneuvering targets are difficult to track for the Kalman filter since the target model of tracking filter might not fit the real target trajectory and the statistical characteristic of the target maneuver are unknown in advance. In order to track such a heavy maneuvering target, the estimation of the target turn-direction is necessary. The two-stage estimator using advanced circular prediction which considers the target turn-direction is proposed for maneuvering target tracking. Simulation results are given for a comparison of the performances of our proposed scheme with that of conventional tracking filters.
ic981049.pdf (From Postscript) TOPHoward A Lazoff, BBN Technologies (U.S.A.)
Multistatic active sonar systems are being developed for the mission of tracking enemy submarines in harsh underwater enviromnemts. This paper will focus on a revolutionary new method with which to track a target. A fuzzy logic based tracker has been developed which performs remarkably better than a Kalman filter tracker. This is accomplished through the use of additional, non-kinematic information about each of the detections. The fuzzy logic engine combines these additional clues with the kinematic clues. This framework allows for the implementation of user-designed rules which take advantage of the additional information that is provided as input to the tracker. This additional information, effectively handled, yields a significant improvement in tracker performance.
ic981752.pdf (From Postscript) TOP
Ning Ma, Chinese University of Hong Kong (Hong Kong)
Didier Vray, CREATIS, INSA (France)
This work is concerned with the estimation of the bottom backscattering coefficient as a function of frequency and of incident angle which is important for bottom imagerying with wideband sonar. Generally, the backscattering coefficient is studied for a given frequency and a fixed angle. Meanwhile the backscattering depends not only on the angle, but also on the frequency, the conventional methods can not be used for the wideband sonar signals analysis. In our work, a wideband chirp sonar (20-140kHz) with -3dB half-angle 12 degree has been used to collect the lacustrine bottom echoes, so the dependence of the backscattering coefficient on the frequency and the incident angle is studied at the same time. An angle-frequency representation is obtained by using the Chirp Adapted time-frequency representation which gives an approximate energy distribution for chirp signals. The proposed method is used for the sand bottom and the pebble bottom echo analysis.
ic981339.pdf (From Postscript) TOPRobert B. MacLeod, Naval Undersea Warfare Center (U.S.A.)
This paper explores the statistical properties of underwater reverberation present in active sonar systems. The interferenceto signal processing which results from reverberation can be extensive, and is particularly acute when the boundaries (surface, bottom) of the water column are nearby. Of particular interest are situations where there may be weak targets masked by reverberation dominating the returning signal. The reverberation will be represented as the output of a linear system with the transmitted signal as an input. The random nature of the reverberation will be accounted for by using random parameters in the linear model, the most important of which are those parameters impacting the spatial distribution of the reverberation. Time delay estimation will be used to analyze reverberant signals obtained from a sonar system operating in a shallow water environment. The statistics of the linear models obtained from these analyses will be computed and discussed.
ic981611.pdf (From Postscript) TOP
Vladimir M. Kudryashov, N.N.Andreev Acoustic Institute (Russia)
Leonid S. Vilentchik, MCB (Russia)
Propagation of acoustic signals along a range-dependent track in the Arctic Basin is considered. The structure of the envelope of the temporal correlation function of a narrowband noise signal propagation in a waveguide is investigated. The form of a model pulse is compared with the wave form obtained in acoustic monitoring in the Arctic Basin. Calculations were carried out with a program based on the coupled mode method. This program takes into account the hydroacoustic waveguide parameters affecting the amplitude-time signal structure. This allowance yielded a satisfactory agreement between calculations and the experiment. We considered a method, which operates when the signal-to-noise ratio is less than unity.
ic981466.pdf (From Postscript) TOP