V. I. Turchin

Experimental results of localization of moving underwater signal by adaptive beamforming

The problem of weak moving signal localization and tracking in the presence of single motionless strong interference is investigated using real data of an underwater experiment in the Baltic sea (Sept. 1990) with a horizontal receiving array of 64 hydrophones and with two independent powerful narrowband sources imitating the signal and interference. Three simple adaptive beamforming methods were employed for the experimental data processing. The first one is based on the well-known projection approach to adaptive beamforming, the second method uses the adaptive canceler approach (also termed the dipole pattern method), and the third method combines these approaches. The signal-to-interference power ratio (SIR) threshold of the signal localization and tracking is evaluated by a special technique, which allows examination of the considered algorithms with change of the SIR in consecutive order. The results of the data processing show the high possibilities of signal localization in the presence of strong interference. The combined method performs better than the methods considered and enables localization of the signal source up to an SIR/spl sime/-25 dB. >

Nonwave field processing using sensor array approach

Abstract The application of sensor array processing methods for estimation and localization of wavefield sources is well known and has been intensively studied in literature. In this paper we extend sensor array processing approach to estimating the parameters of the fields of nonwave nature (the so-called nonwave fields). Considering the static and the diffusion field as typical examples of nonwave fields, and assuming that measurements are carried out by an antenna array, we derive the Cramer-Rao bounds of source parameter estimation errors. These theoretical results are completed by the experimental results of localization of the diffusion sources in distilled water by chemical sensor array, showing high performance of sensor array processing approach to the problem considered. A modified version of the well-known CLEAN deconvolution algorithm has been used for experimental data processing.

Experimental studies of sound diffraction by moving inhomogeneities under shallow-water conditions

The experimental data on the sound propagation and diffraction by moving test inhomogeneities under lake conditions are presented. It is shown that the diffracted signals under multimode propagation are adequately described by simplified theoretical models proposed earlier. The detection of the diffracted signals against the background of a fluctuating direct signal is demonstrated for the reception by a horizontal or vertical array. It is also shown that the direct and diffracted signals observed in the lake are similar in their characteristics to the signals in a shallow sea, which allows one to use the lake experiment for testing various underwater acoustic techniques intended for shallow-sea conditions.

Comparative analysis of tomographic methods for the observation of inhomogeneities in a shallow sea

Several procedures are proposed that allow one to determine the parameters of motion of an inhomogeneity crossing the propagation path between a source of an acoustic signal and a receiving array without the use of any detailed description of the medium (the sound velocity profile, the bottom parameters, etc.). The potentialities and characteristic features of the proposed approach are analyzed within the framework of a one-dimensional waveguide propagation model. A comparative analysis of the reliability of inhomogeneity observations is performed on the basis of a representative experimental data set obtained from a lake experiment for the cases of using the procedures of coherent space-time processing of signals in antenna arrays and the procedures with a spatial and temporal incoherent accumulation.

The use of receiving arrays for measuring underwater noise levels of moving sources

A method of measuring underwater noise levels of moving ships with the use of a vertical receiving array is considered. An algorithm is proposed for synthesizing the weight vector that provides a given measurement accuracy with maximal noise suppression for the cases of an interference with a known structure and an a priori unknown interference (the adaptive synthesis). Results of both numerical simulation of the method and its experimental testing under actual sea conditions are presented.

Experiment on estimating the coordinates of an emitter on the Black Sea shelf

The paper presents the results of an experiment, conducted in Sukhumi Bay, on estimating the depth of a wideband emitter and its distance to a vertical reception array moored close to shore. The coordinates of the emitter were reconstructed from acoustic measurement data. The solution to the formulated problem was complicated by the absence of reliable information on the bottom relief and bottom parameters. It is demonstrated that under such conditions, matched field processing can be applied to estimate the coordinates of the emitter. For this, when solving the inverse problem, the components of signals without bottom reflection were used as the input parameters.

Estimation of the background noise level with a horizontal array against spatially uncorrelated and structural interferences

A method of estimating the isotropic sea noise level with a horizontal array in the presence of uncorrelated interference and interference with a complex spatial structure is proposed and experimentally tested. The algorithm is based on the approximation of the Capon spatial spectrum of the received signal using a model Capon spectrum for the sum of isotropic noise and uncorrelated interference. A numerical simulation is carried out to study the dependence of the accuracy of the proposed method on the interference intensity, the distance from the array to the sources of structural interference, and the number of structural interference sources. It is shown that the use of the Capon spectrum provides a strong suppression of an intense structural interference source positioned near the array. The efficiency of the proposed method is confirmed experimentally.

Inverse Aperture Synthesis in an Acoustic Dark Field

A method is proposed for extracting the signal scattered by a moving acoustic screen and for reconstructing the image of the scatterer. The results of the preliminary numerical calculations performed for a free space agree well with the results of the full-scale experiment in a lake. A good agreement between theory and experiment is achieved with an aperture synthesis by the signal magnitude. The characteristic feature of the proposed method of aperture synthesis is the use of an extended acoustic array in the target tracking mode of operation. This provides an additional condition for the determination of the parameters of the experiment, thus allowing one to determine two such parameters.

Remote sensing of moving wide-band sources

We consider the methods of covariance matrix reconstruction for sensing an extended noise-like emitter which moves near the receiving antenna array and is modelled as a random longitudinal distribution of external elementary sources. Linearized maximum-likelihood equations for the desired covariance matrix are obtained in the cases of a priori known and unknown covariance matrix of the noise background. The variance of estimates for the elements of the covariance matrix characterizing the emitter is studied.

Sensor array approach to nonwave field processing

The application of sensor array processing methods for estimation and localization of wavefield sources is well-known. We extend the sensor array processing approach to estimating the parameters of the fields of a nonwave nature (the so-called nonwave fields). Considering the static and diffusion fields as typical examples of nonwave field, we derive the Cramer-Rao bounds of source parameter estimation errors. These theoretical results are completed by the experimental results of localization of diffusion sources in distilled water by a chemical sensor array, showing potentially high performance of sensor array approach. A modified version of the well-known CLEAN deconvolution algorithm has been used for experimental data processing. The nonwave field sensor array processing can find various applications such as localization of pollution sources and another types of admixtures, detection of metallic masses and wandering currents, etc.