Towed Array Sonar System Research Articles

Development of vector hydrophone using thickness–shear mode piezoelectric single crystal accelerometer

In this study, a vector hydrophone was developed for a towed array sonar system using a shear type accelerometer. In general, inertia type vector hydrophones using accelerometers have higher sensitivity than multimode vector hydrophones. However, the sensitivity still needs to be enhanced as much as possible for practical application. For the purpose, the effect of the structural parameters of a shear type accelerometer on the receiving voltage sensitivity (RVS) of the vector hydrophone was rigorously analyzed, and the structure of the vector hydrophone was optimized to maximize the RVS. The developed vector hydrophone has an external diameter of 23 mm and the minimum RVS over the given frequency range of -201.4 dB. It was also verified that the designed vector hydrophone exhibits the characteristic of a dipole mode beam pattern. Furthermore, a prototype of the vector hydrophone was fabricated with the optimal dimensions, and its acoustic characteristics were measured to verify the validity of the design. The vector hydrophone developed in this work has the highest feasible RVS over the desired frequency range in comparison with other types of vector hydrophone like the multimode hydrophone.

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.

센서 바이어스를 보상하는 칼만필터 기반의 예인 선배열 센서 형상 추정 기법

TASS(Towed Array Sonar System) is a sonar system which tows the sensor array behind a platform. Array shape is generally assumed to be a straight line. But the array shape is often distorted by oceanic current or platform maneuvering which causes the performance loss of signal processing method like beamforming. So array shape estimation methods are needed. Typically the method based on Kalman filter using heading sensor is used. In practice, the measurement is corrupted by biases which are caused by rotation of the tow cable, varying magnetic fields and slowly varying stresses in the mechanical construction. Although they can't be calibrated but can be estimated. In this paper, we suggest the array shape estimation method based on Kalman filter compensating the sensor biases.

Numerical investigation of the dynamics for low tension marine cables

This paper presents a numerical investigation into the dynamics of marine cables which are extensively used in offshore industry. In this numerical study, the Euler-Bernoulli beam model is adopted to develop the governing equations of the cable. Bending stiffness is considered to cope with the low tension problem in local area of towing cable, and thus a more accurate solution with the consideration of the axial elongation can be given. The derived strongly-coupled and nonlinear governing equations are solved by a second-order accurate, implicit, and large time step stable central finite difference method. The quadratically convergent Newton-Raphson iteration method is applied to solving the discrete nonlinear algebraic equations. Then a towed array sonar system (TASS) problem is studied. The numerical solutions agree reasonably well with the experimental data and the simulated results of the references. The specified program of the present paper shows great robustness with high efficiency.

A numerical and experimental study on dynamics of a towed low tension cable

This paper presents a numerical and experimental investigation into the dynamic behaviour of a towed low tension cable applicable to a towed array sonar system for detecting submarines. In the numerical study, an implicit finite difference algorithm is employed for solving the three-dimensional cable equations. Bending stiffness is considered in order to cope with the low tension problem. Fluid and geometric non-linearities are solved by Newton-Raphson iteration. Block tri-diagonal matrix method is applied for the fast calculation of very large matrices. In order to verify the numerical results and to observe real physical phenomena, an experiment was carried out for a 6 m cable in a deep towing tank. In the experiment, the cable was towed in two different ways; one was towed at a constant speed and the other was towed at a constant speed with top end horizontal oscillations. Cable tension and shear forces were measured at the top end. Numerical results are compared with experimental data. Good agreements are only achieved by employing enhanced drag coefficients due to vortex induced vibrations. It is also found that in the numerical modelling, non-uniform element lengths are necessary to cope with the sharp variation of tension and shear forces near the top fixed end.

Supporting structure of hydrophones for towed array sonar system

A support structure of hydrophones for a towed array sonar system includes elastic members arranged in each sensor package and adapted to support a hydrophone received in the sensor package while attenuating vibrations transmitted to the sensor package. External vibrations, such as vibrations generated due to the running of a towing vessel or vibrations induced due to motions of a towing cable, which are irrespective of acoustic waves reflected by a target moving underwater, are attenuated by the hydrophone support structure during the transmission thereof from the sensor package to the hydrophones, so that the hydrophones are suppressed from vibrating due to the external vibrations. Accordingly, it is possible to reduce noise included in output signals of the hydrophones, thereby achieving an improvement in the sensing performance of the towed array sonar system.

Conversion of EX T‐AGOS 14

ABSTRACT The USNS Worthy had been a T‐AGOS 13 Class ocean surveillance ship equipped with a Surveillance Towed Array Sonar system (SURTASS) to collect, process and transmit underwater acoustic signal data to shore facilities for evaluation. Decommissioning of the entire class and removal of the SURTASS system left a vessel with a considerable useful service life, abundant electrical generation capability, and accommodations and working spaces. These features meshed well with the U.S. Geological Survey's need for a research vessel. Preliminary conversion plans and preparation of detailed alteration drawings and specifications were completed. However, after USGS acceptance of the unconverted vessel from the reserve fleet, funding constraints delayed conversion indefinitely, and lay‐up of the vessel was a likely probability.Fortunately, at this time, Raytheon Range Systems Engineering (RSE) was in need of a platform for the Kwajalein Mobile Range Safety System (KMRSS) for the U.S. Army at Kwajalein Atoll (USAKA). The characteristics of the Worthy met KMRSS requirements with a sufficient margin to allow a joint usage agreement and incorporation of features for future USGS use in the conversion design.This paper describes both the USGS and KMRSS vessel design and KMRSS conversion effort.

Implementation of a synthetic aperture processing scheme in a towed array sonar system

This experimental paper is concerned with the implementation of a passive synthetic aperture processing scheme in a towed array sonar system. It addresses theoretical and practical concerns, and the experimental results suggest that the concept of a synthetic aperture towed array system complements the conventional beamformer’s processing results. The acoustic synthetic aperture technique, which has been considered in this study, is the ETAM algorithm [i.e., extended towed array measurements, J. Acoust. Soc. Am. 87, 158–171 (1989)]. Theoretical and experimental studies have shown that the above technique compensates the random phase fluctuations in the data that are introduced by the tow path. This results is an effective extension of the physical aperture of a deployed towed array and consequently provides improved angular resolution performance equivalent to a fully populated long array. Also included in this presentation is a discussion of the development of the computing architecture requirements related to this kind of implementation. It is shown that the development of a next generation signal processor (NGSP) by the Defence Research Establishment Atlantic (DREA) overcomes the limitations normally associated with the implementation of nonlinear algorithms into parallel FFT-based vector processors.

Implementation of adaptive beamforming processing schemes in a towed array sonar system

This experimental paper is concerned with the implementation of the minimum variance distortionless response (MVDR) method [IEEE Trans. 57(8), 1408–1418 (1969)] in a towed array sonar system. The paper discusses the issues associated with the implementation of the MVDR in a real time processing system and examines the robustness of the algorithm using a variety of sea trial data. The performance of an algorithm that pre-processes the data before the MVDR algorithm is applied is also discussed and compared with the standard approach. The experimental results obtained suggest that, as expected, the robustness of the MVDR algorithm is the key to its successful implementation in a real time system. When this condition is met, the MVDR has demonstrated the capability to enhance the conventional beamformer by providing improvements in both angular resolution and detection performance. The implementation of the MVDR algorithm in a real time towed array processing system has necessitated the development of