EM based GLRT Detector for MIMO Active Sonar using Bistatic Reverberation Model
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It is known that the performance of sonar is limited by reverberation, especially, in shallow waters. We study the active MIMO (Multiple Input Multiple Output) sonar detection problem in scenarios limited by reverberation. The bistatic reverberation envelop at the hydrophone of the MIMO array is modeled as delayed and attenuated returns of the transmitted signals from the scattering patches at the ocean floor. Based on this bistatic reverberation ocean channel model, we derive a single snapshot generalized likelihood ratio test (GLRT) detector for MIMO sonar. In the proposed detection algorithm, an EM (Expectation-Maximization) based technique is employed for estimating the scattering strength coefficients in the reverberation model. The theoretical limits on the achievable performance of GLRT and the detection threshold are derived for the narrowband case. The performance of the proposed algorithm is compared with other techniques such as covariance matching and matched filtering. Simulations show that the performance of the proposed detector is quite close to the theoretical limit and outperforms other detection techniques.Keywords:
Narrowband
Target strength
Mid-Frequency bistatic reverberation level is modeled using ray theoretic algorithms. The algorithm assumes multiple forward/backward scatter along with reciprocity in the Propagation paths. The environments modeled are assumed to be range independent in bathymetry, bottom scattering and surface scattering. Mid-Frequency bistatic scattering algorithm is used as a scattering model. A comparison of predicted reverberation versus time with measured data is presented to verify the bistatic reverberation model. The result demonstrates that it is possible to obtain reasonable reverberation Predictions in experimental site.
Reciprocity
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Bistatic and monostatic reverberation data were recorded in the 2001 Asian Sea International Acoustic Experiment (ASLIAEX).A model based on the normal mode theory has been developed to calculate bistatic bottom reverberation in shallow water and to explain the recorded data.The comparisons between the monostatic and bistatic reverberation data are discussed,and the comparisons between model predictions and measured bistatic reverberation data are also presented.The numerical and experimental results show that the numerical predictions from the bistatic reverberation model fit the experimental data well,and the long-range bistatic reverberation with a time delay can be approximately expressed by the monostatic reverberation data.
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Theoretical formula of calculating the bistatic bottom reverberation in bistatic geometry structure was deducted to explain the cause,transmission and the effect to the receiving sonar of the bottom reverberation under the bistatic geometry.A two-dimensional bistatic bottom reverberation model was established within the seabed.Upon these,simulation of the bistatic reverberation was made when the test track,receive angle,distance between the source and the receiver,and transmit delay were changed separately,and the curves of the reverberation level and some initial analyses were given.The results showed that the bistatic bottom reverberation was different from the monostatic situation as it has something to do with the input azimuth angle,the distance between the source and the receiver,etc.
Seabed
Underwater Acoustics
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According to active sonar equation,we predict the performance of active detection sonar under reverberation,discuss the influence of the frequency of active detection sonar on the detection range,and compare the detection ranges of the active sonar under different reverberation backscattering strength.The results show that the detection range of the active sonar decreases with decreasing frequency,and the performance of the active sonar enhances and the detection range extends with the weakening of reverberation backscattering strength.This study may be useful for selecting pa-rameters of active detection sonar to enhance its performance in engineering.
Target strength
Synthetic aperture sonar
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In ASIAEX2001, the experiment data of monostatic and bistatic reverberation were recorded. There is much difference between the two-experiment data: the monostatic reverberation loss and the vertical correlation are all much less than those of the bistatic. To explain the phenomena, on the basis of ray-mode reverberation theory and three-dimensional scattering model, the expressions of the bistatic reverberation loss and the vertical correlation are put forward. The relations between the monostatic and bistatic reverberation are discussed and compared with the experiment data. The calculation and the experiment data indicate: after a time delay (the transmission time from the source to the receiver), the long-range bistatic reverberation loss and the vertical correlation can be approximately expressed by the monostatic reverberation loss and the vertical correlation.
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The estimation and removal of the time-varying two-way impulse response to environmental scatterers from broadband reverberation data is considered for increasing the signal-to-noise ratio of sonar returns from targets in the water column. Spectrograms of simulated and real reverberation time series data from active sonars in the mid-frequency range show strong evidence of interference patterns which give clues to the number of important paths to environmental scatterers as well as their depth in the water column. In this talk we consider the estimation of a time dependent de-convolution filter for the removal of these environmental reverberation returns from active sonar data. Issues regarding the degrees of freedom required for the efficient implementation of this filter and the stability of these estimates are considered. Simulation results are shown which demonstrate the potential gain of using this approach to partially null the impact of environmental scatterers in active sonar data.
Impulse response
Spectrogram
Finite impulse response
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One of the major problems for active sonar detector is the presence of reverberation. Since the reverberation has both spatially and temporally varying characteristics, a Space Time Adaptive Processing (STAP) technique is used to adapt the processing according to the varying environment. The contribution of this paper is a low complexity STAP scheme for reverberation cancellation in active sonar detection, making use of polyphase filter architecture based sampling rate conversion.
Polyphase system
Sonar signal processing
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This paper explores the statistical properties of underwater reverberation present in active sonar systems. The interference to 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 is represented as the output of a linear system with the transmitted signal as an input. The random nature of the reverberation is 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 is 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 are computed and discussed.
Sonar signal processing
SIGNAL (programming language)
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For the problem that the bistatic sonar can not detect the target near the baseline because of the interference of direct wave,a method based on the Babinet's principle is proposed for bistatic sonar detection.The basic idea is that the forward scattering signal is accumulated and detected for a long time in the blind zone of bistatic sonar.The result shows that the target strength formula derived in this paper is consistent with that of the rotational ellipsoid.The simulation results show that the forward scattering signal strength distribution looks like an eye.It is feasible to detect the slowly moving target in the blind zone with the proposed method.
Target strength
SIGNAL (programming language)
Ellipsoid
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