Sonar Array Research Articles

Spatial rotation technique with application to unmanned underwater vehicle (UUV) sonar arrays

A spatial rotation technique in application to unmanned underwater vehicle (UUV) sonar arrays is proposed. The essence of the technique is to rotate the signals of interest from the array coordinates to geodetic coordinates while providing robustness against interferences and preserving the white noise property at the output. Convex formulation of the rotation matrix design problem is derived using the semi-definite relaxation technique and the optimal solution is obtained by rank-one decomposition theorems. Using the authors’ technique, the subspace-based direction of arrival estimation methods can get large snapshot support for weak sources in the UUV motion-case.

Constrained robust submodular sensor selection with application to multistatic sonar arrays

The authors develop a framework to select a subset of sensors from a field in which the sensors have an ingrained independence structure. Given an arbitrary independence pattern, the authors construct a graph that denotes pairwise independence between sensors, which means those sensors may operate simultaneously without interfering. The set of all fully-connected subgraphs (cliques) of this independence graph forms the independent sets of matroids over which the authors maximise the average and minimum of a set of submodular objective functions. The average case is submodular, so it can be approximated. The minimum case is both non-submodular and inapproximable. The authors propose a novel algorithm GENSAT that exploits submodularity and, as a result, returns a near-optimal solution with approximation guarantees on a relaxed problem that are within a small factor of the average case scenario. The authors apply this framework to ping sequence optimisation for active multistatic sonar arrays by maximising sensor coverage for average and minimum case scenarios and derive lower bounds for minimum probability of detection for a fractional number of targets. In these ping sequence optimisation simulations, GENSAT exceeds the fractional lower bounds and reaches near-optimal performance, and submodular function optimisation vastly outperforms traditional approaches and nearly achieves optimal performance.

Thinned Array Design With Minimum Number of Transducers for Multibeam Imaging Sonar

A large number of transducers employed in the multibeam imaging sonar array significantly increases the hardware complexity, costs, and computational load. Although a great amount of work has been done to minimize the number of transducers in the array, one can verify that these methods do not provide optimal results when applied to the case of multiple beams. In this paper, a novel thinning method is proposed for multiple-beam conditions where the number of transducers is minimized by an iterative process. Optimal common transducers’ positions are selected by a wind-driven optimization (WDO) algorithm, and transducers’ weights are optimized by convex optimization in order to suppress the peak sidelobe level (PSLL). The performance of the proposed method is evaluated via simulations and experiments. Results show that the method is applicable to the minimization of the number of transducers under hundreds of beam conditions, and consequently reduces the complexity of the imaging sonar system with imaging performance still acceptable.

Design and development of route planner for Unmanned Surface Vehicles

This paper describes the development of a route planner for Unmanned Surface Vehicles (USVs) focused on the study of an operational scenario for a specific mission – Anti-Submarine Warfare (ASW). Through the design and implementation of a simulation model, the effect of the different factors that particularly influence ASW is analyzed, such as search pattern, speed and sensor type; dipping sonar or towed array sonar (TAS). By obtaining a measurement of effectiveness, the USV’s response in the deployment of this type of mission can be defined using time to detect the threat in a search area, as parameters to measure the performance.

Analysis on spectra of hydroacoustic field in sonar cavity of the sandwich elastic wall structure

In this paper, the characteristics of the mechanical self - noise in sonar array cavity are studied by using the elastic flatbed - filled rectangular cavity parameterization model. Firstly, the analytic derivation of the vibration differential equation of the single layer, sandwich elastic wall plate structure and internal fluid coupling is carried out, and the modal method is used to solve it. Finally, the spectral characteristics of the acoustic field of rectangular cavity of different elastic wallboard materials are simulated and analyzed, which provides a theoretical reference for the prediction and control of sonar mechanical self-noise. In this paper, the sandwich board as control inside the dome background noise of a potential means were discussed, the dome background noise of qualitative prediction analysis and control has important theoretical significance.

Beamforming using subspace estimation from a diagonally averaged sample covariance.

The potential benefit of a large-aperture sonar array for high resolution target localization is often challenged by the lack of sufficient data required for adaptive beamforming. This paper introduces a Toeplitz-constrained estimator of the clairvoyant signal covariance matrix corresponding to multiple far-field targets embedded in background isotropic noise. The estimator is obtained by averaging along subdiagonals of the sample covariance matrix, followed by covariance extrapolation using the method of maximum entropy. The sample covariance is computed from limited data snapshots, a situation commonly encountered with large-aperture arrays in environments characterized by short periods of local stationarity. Eigenvectors computed from the Toeplitz-constrained covariance are used to construct signal-subspace projector matrices, which are shown to reduce background noise and improve detection of closely spaced targets when applied to subspace beamforming. Monte Carlo simulations corresponding to increasing array aperture suggest convergence of the proposed projector to the clairvoyant signal projector, thereby outperforming the classic projector obtained from the sample eigenvectors. Beamforming performance of the proposed method is analyzed using simulated data, as well as experimental data from the Shallow Water Array Performance experiment.

Flow Noise Calculation and Experimental Study for Hydrophones in Fluid-Filled Towed Arrays

Understanding the physical features of the flow noise for hydrophones in a fluid-filled towed array is important for designing a towed line array sonar. The flow noise of hydrophones in fluid-filled towed arrays generated by the turbulent pressure is derived by the frequency–wave number decomposition method. The results show that the flow noise increases rapidly with the towed speed and decreases with the length of the hydrophone. Meanwhile, the flow noise is closely related to the material parameters of the elastomer tube. It decreases with the attenuation factor, outside radius, and thickness of the elastomer tube. Furthermore, a spatial filter designed by the constant sector inverse-beamforming method is used for suppressing the tow-ship-radiated noise and the ambient noise from the sensor data. The analysis results of the experimental data are consistent well with the theoretical values, which indicate that the tow-ship-radiated noise and the ambient noise are suppressed effectively by the spatial filter. In addition, the correlation features of the flow noise received by the acoustic array are analyzed, which is important for the sonar system design.

The performance analysis of sonar target tracking based on pressure hydrophone arrays

For the linear array sonar that consists of pressure hydrophones, it is difficult to solve the problem of port/starboard ambiguity. To estimate the target’s real azimuth accurately, the conventional beam forming methods of different arrays which include linear array, arc array, cross array and Y-shaped array were analysed. Based on the port/starboard discrimination ability and beam width, the sonar target tracking performance of different arrays was compared. It is shown that all arrays except the linear array could discriminate the real target, and the arc array’s effect is the best.

German Navy sonar development during the two world wars and interwar years

In the German Navy, as in the UK and America, the development of underwater acoustical detection was shaped by institutional, political, and technical constraints and in response to tactical events. German hydrophone development in WWI was less advanced than that of the Allies, who focussed on combating an all-out U-boat war. The German Navy did not develop the variety of hydrophones developed by the Allies in particular the towed hydrophone array of the American Navy, which nevertheless inspired their passive sonar arrays known as “Gruppenhorchgerät” (GHG), German for “group listening device” in the interwar years, developed for the long-range protection of their capital ships, until 1935 with the signing of the Anglo German Naval Agreement when they commenced their submarine building program. For strategic reasons, Germany continued to concentrate on pro-submarine research so that at the start of WWII the German Navy had developed sophisticated GHG systems available which they improved further into the “Balkon” system of the later high-speed U-boats, Type XXI and XXVI. Their operational echo-ranging Asdic equipment was tactically inferior to that of the Royal Navy, and some interesting prototypes in development did not reach active service.

Synthetic aperture sonar interferometry for detailed seabed mapping: Performance considerations

Synthetic Aperture Sonar (SAS) interferometry is a technique for detailed mapping of the seabed, with the potential of very high resolution and wide swaths simultaneously. There are several specific challenges to overcome for the technique to reach its full potential. These differ from other mapping sensor technologies, e.g., multibeam echosounders (MBES), and interferometric sidescan sonars (ISSS). In this talk, we describe the principle of SAS interferometry with emphasis on the estimation part, strongly inspired by the similar principle in synthetic aperture radar (SAR). We describe the limiting factors in using SAS interferometry for seabed depth estimation. These are related to the host platform, the measurement geometry, the sonar array design, and the signal processing. We construct an error budget where we categorize the different components that affect the overall performance. We also describe the choices and tradeoffs available in the signal processing for a given set of measurements. We show example images and depth estimates from the Kongsberg HISAS interferometric SAS collected by a HUGIN autonomous underwater vehicle.

능동 소나 배열의 개념 설계를 위한 반복법 기반 배열 해석

능동 소나 배열의 개념 설계를 위한 반복법 기반 배열 해석

삼중 배열 소나를 위한 강인한 적응 빔형성 기법

본 논문에서는 삼중 배열 소나를 위한 강인한 적응 빔형성 기법을 제안한다. 제안하는 빔형성은 삼중 배열 소나를 이용하여 불일치에 강인하고 좌우구분이 가능한 빔을 만드는 방법으로 두 단계로 이루어져 있다. 먼저 각 삼각 센서 별로 표적 신호의 좌우 방위 구분을 위한 카디오이드 빔을 생성하며, 각 삼각 센서(Triplet)에 대한 회전각을 반영하여 지연차 방법을 통해 빔을 형성한다. 다음으로 인접 표적에 의한 간섭을 최소화하기 위해 적응 빔을 생성한다. 삼각 센서 별로 얻은 카디오이드 빔을 선배열에 대한 입력 신호로 하여 선배열에 대한 적응 빔형성 기법을 카디오이드 빔에 적용한다. 시뮬레이션을 통해 본 논문에서 제안하는 기법이 기존 기법 대비 표적에 대한 좌우 구분 및 불일치에 강인함을 확인하였다. We propose a robust adaptive beamforming algorithm for triplet array sonar. The proposed beamforming algorithm obtains robustness to mismatches, left/right discrimination, and has two steps. The first is a cardioid beamformer, which supports left/right discrimination of target signals. It applies the conventional delay-and-subtract to each triplet's signal with its rotation angle and obtains multiple cardioid beams. The second is a robust adaptive beamforming to minimize nearby interferences. We regard cardioid beams as input signals of a line array and apply an adaptive beamforming algorithm to the cardioid beams. Simulations results show that the proposed algorithm provides significantly better performance than the conventional algorithms, while supporting left/right discrimination of target signals.

Design of SONAR Array for Detection of Bottoming Cylindrical Objects

Design of SONAR Array for Detection of Bottoming Cylindrical Objects

DOA estimation based on multiple beamspace measurements sparse reconstruction for manoeuvring towed array

The port-starboard ambiguity in the conventional single towed linear array sonar is one of the most deceiving obstacles which exist in the way of development of spatial spectrum estimation. In order to improve the performance of target detection and Direction of Arrival (DOA) estimation, this paper proposes a novel spatial spectrum sparse reconstruction method based on multiple beamspace measurements (MBM-SR). An array sparse signal model for manoeuvring towed array is established. Then the Mutual Incoherent Property (MIP) is analyzed to ensure the proposed algorithm possessing better spatial spectrum reconstruction property. Simulation results demonstrate that, compared with Conventional Beam Forming (CBF) algorithm, the proposed algorithm has evident advantage in ambiguity suppression ratio (ASR) and estimation performance.

Spatial Spectrum Sparse Reconstruction for Maneuvering Towed Array

The port-starboard ambiguity in the conventional single towed linear array sonar is one of the most deceiving obstacles for the spatial spectrum estimation. In order to improve the performance of target detection and Direction of Arrival (DOA) estimation, a spatial spectrum sparse representation model is established using multiple beam-space measurements. The forward-backward operator splitting method is adopted for solving the sparse optimization problem. Simulation results demonstrate that, compared with Conventional Beam Forming (CBF) method, the proposed method has evident advantages in ambiguity suppression and estimation performance.

Determining the probability of correct resolution of the left–right ambiguity in towed array sonar

When a towed sonar array is straight, it has the difficulty that it cannot distinguish a contact on the left from one at the same angle on the right. When the array isnotstraight and its shape known, we calculate the probability that the left–right ambiguity is resolved correctly, using the Neyman–Pearson hypothesis testing framework, assuming a delay-sum beamformer, a single-frequency contact, and Gaussian noise. We also initially consider the noise field to be uncorrelated and show that the evaluation of the probability of correct resolution reduces to evaluating a one-dimensional integral. We find, as expected, that the probability increases, as the signal-to-noise ratio and the lateral deviation of the array from straight increase. For demonstration purposes, we also evaluate the probability of correct resolution for two representative shapes the array might assume in practice. Finally, we consider a more realistic, correlated noise field and we show that the initial assumption of an uncorrelated noise field provides a good approximation when the lateral deviation of the array is sufficiently large.

Carbonized Electrospun Nanofiber Sheets for Thermophones.

Thermoacoustic performance of thin freestanding sheets of carbonized poly(acrylonitrile) and polybenzimidazole nanofibers are studied as promising candidates for thermophones. We analyze thermodynamic properties of sheets using transport parameters of single nanofibers and their aligned and randomly electrospun thin film assemblies. The electrical and thermal conductivities, thermal diffusivity, heat capacity, and infrared blackbody radiation are investigated to extract the heat exchange coefficient and enhance the energy conversion efficiency. Spectral and power dependencies of sound pressure in air are compared with carbon nanotube sheets and theoretical prediction. Despite lower thermoacoustic performance compared to that of CNT sheets, the mechanical strength and cost-effective production technology of thermophones make them very attractive for large-size sound projectors. The advantages of carbonized electrospun polymer nanofiber sheets are in the low frequency domain (<1000 Hz), where the large thermal diffusion length diminishes the thermal inertia of thick (∼200 nm) nonbundled fibers and the high intrinsic thermal conductivity of fibers enhances the heat exchange coefficient. Applications of thermoacoustic projectors for loudspeakers, high power SONAR arrays, and sound cancellation are discussed.

누적 일괄추정 기법을 이용한 수동 선배열 소나 방위 주파수 -표적기동분석 연구

Bearing and frequency measurements of TMA (Target Motion Analysis) in passive line array SONAR have lower bearing rate and frequency doppler, and are not detected or tracked continuously because of various ocean environments. This is a main reason to effect the TMA performance and it takes a long time to get TMA solutions. We propose the bearing and frequency TMA(BFTMA) using accumulative batch estimation to solve the TMA problem of line array passive SONAR. The accumulative batch estimation structure is based on MLE (Maximum Likelihood Estimation) but used accumulative measurements. The accumulative batch estimation is applied for the BFTMA with nonlinear Kalman filter to estimate the target range, speed and course. Simulation and sea data analysis were carried out to verify the performance and applicability of the proposed techniques.

예인 음탐기용 케이블 개발

Cables for Towed Array Sonar System(TASS) were developed. In order to verify the performance of cables, environmental and operational conditions as well as functional requirements were investigated during design stage. Double armored high and low voltage integrated cable for towed body and two kinds of cables, armored and light weight power and optic hybrid cables for towed array sensor system were developed by modeling and simulation. Customized manufacturing process and test method, such as foam extrusion and dynamic fatigue test were applied to this development. In conclusion, underwater towed hybrid cable with high tensile strength and compact structure were developed.

Bio-inspired broadband sonar array prototypes and underwater experiments for two- and three-dimensional acoustic imaging applications

Underwater sonar imaging relies upon the information contained in time correlation delays across numerous channels. Designing higher resolution imaging systems currently requires increasing the array aperture to wavelength ratio (L / λ), where L is the effective array length and λ is the acoustic wavelength in the medium. This fundamental constraint leads engineers down the path of adding a significant number of channels to a sonar design, which in turn increases array complexity and cost. Our research in bio-inspired sonar has revealed an approach that circumvents this constraint by exploiting bandwidth in addition to time-delay for the angular imaging process. Presented will be the results of a 2-channel underwater prototype tested in an acoustic tank and design work toward a 3-channel prototype for extending imaging to elevation angles. This work represents ongoing efforts toward developing a compact, low-cost broadband underwater sonar for near- to mid-range imaging and classification. Future integration with an autonomous underwater vehicle will demonstrate this technology for simple obstacle detection and avoidance of complex objects. [Work supported by ONR and internal investments by NUWC Division Newport.]