Woo-Shik Kim

Multi-static scattering characteristics of submerged objects with experimental investigation

The scattering characteristics of target echoes are essential for detecting and classifying the submerged objects. The target strength, which is widely used in mono-static sonar system, is also important in multi-static sonar system to identify the submerged target. In this presentation, a series of experiments in the acoustic water tank was conducted to measure the target echoes from submerged cylinder-shaped target with multi-static measurement system, which consists of a single transmitter and 16 receivers. The target strengths are presented in 2-dimensional plane as a function of receiver position according to target aspect angle. The numerical simulation results based on Kirchhoff approximation are presented to explain some characteristics of the measured multi-static target echoes. [Work supported by Agency for Defense Development, Republic of Korea.]

Direction-of-Arrival Estimation for the Ring-Type Multimode Vector Hydrophone based on the Pressure Gradient-Acceleration Relationship

Conventional hydrophones can only measure acoustic pressure. To measure both acoustic pressure and incident direction, various types of vector hydrophones have been researched. In this paper, we deal with a ring-type multimode vector hydrophone divided into 4 elements and present a direction-of-arrival (DoA) estimation method based on the pressure gradient-acceleration relationship. The performance of the presented method is analyzed by the simulation based on the sensor modeling and is verified by the water tank experiment. The proposed method could work under the multi-frequency condition and may be utilized in many applications due to its low computation complexity.

Investigation of Target Echoes in Multi-static SONAR System - Part I : Design for Acoustic Measuring System

The target echoes contain information on the target such as the orientation, kinematics, and internal structure, as well as the external geometrical shape of the target. In addition, the pattern of the target echoes depends on the arrangement of the transmitters and receivers in space. Therefore, the study of the target echoes in a multi-static SONAR system can be useful for detecting and tracking submerged objects using an underwater surveillance system. For this purpose, an acoustic measuring system for multi-static target echoes was designed and tested in an acoustic water tank. Some preliminary data are presented and discussed.

Investigation of Target Echoes in Multi-static SONAR system - Part II : Numerical Modeling with Experimental Verification

A multi-static SONAR system consists of the transmitters and receivers separately in space. The active target echoes are received along the transmitter-target-receiver path and depend on the shape and aspect angle of the submerged objects at each receiver. Thus, the target echo algorithm used with a mono-static system, in which the transmitter and receiver are located at the same position, has limits in simulating the target echoes for a multi-static SONAR system. In this paper, a target echo modeling procedure for a 3D submerged object in space is described based on the Kirchhoff approximation, and the SONAR system is extended to a multi-static SONAR system. The scattered field from external structures is calculated on the visible surfaces, which is determined based on the locations of the transmitter and receiver. A series of experiments in an acoustic water tank was conducted to measure the target echoes from scaled targets with a single transmitter and 16 receivers. Finally, the numerical results were compared with experimental results and shown to be useful for simulating the target echoes/target strength in a multi-static SONAR system.

A Study on the Underwater Target Detection Using the Waveform Inversion Technique

ABSTRACT: A short-range underwater target detection and identification techniques using mid- and high-frequency bands have been highly developed. However, nowadays the long-range detection using the low-frequency band is requested and one of the most challengeable issues. The waveform inversion technique is widely used and the hottest technology in both academia and industry of the seismic exploration. It is based on the numerical analysis tool, and could construct more than a few kilometers of the subsurface structures and model-parameters such as P-wave velocity using a low-frequency band. By applying this technique to the underwater acoustic circumstance, firstly application of underwater target detection is verified. Furthermore, subsurface structures and it’s parameters of the war-field are well reconstructed. We can confirm that this technique greatly reduces the false-alarm rate for the underwater targets because it could accurately reproduce both the shape and the model-parameters at the same time.Keywords: Waveform inversion, Target detection, Low-frequency detection, Model-parameter estimationPACS numbers: 43.30.Pc, 43.30.Vh †Corresponding author: Ho Seuk Bae

Development of the SONAR System for an Unmanned Surface Vehicle

ABSTRACT Recently, unmanned systems are largely utilized in various fields due to the persistency and the least operational risk and an unmanned surface vehicle(USV) is the one of the representative application in the naval field. To assign multiple roles to an USV, we developed a sonar system which consists of a forward detecting sonar for the long-range detection, a downward detecting sonar for the small target scan and identification, and a strut type body for mounting sonar systems. In this paper, we described the developed sonar system for USV and the sea test results for verifying system performance. The test results showed that the developed sonar system was able to detect the underwater target about several kilometers away and could recognize a small object at the downside of the sonar system. We expect that the developed sonar system will be easily applied to other unmanned platforms without serious consideration.Key Words : Unmanned Surface Vehicle(무인수상정), Sonar System Development(소나시스템 개발), Forward Detecting Sonar(전방탐지소나), Downward Detecting Sonar(하방탐지소나)

Computationally efficient algorithm for Kirchhoff approximation

In order to simulate the target echoes scattered from submerged underwater objects, Kirchhoff approximation is widely used for high frequency region. Since Kirchhoff integration is based on integrating the contributions from discretized boundary elements, the computation can be time-consuming especially for broadband pulses. In this study, a numerically efficient method for generating the scattered signal in time domain based on convolution is proposed and tested. It is shown that the computational time can be reduced by an order of 10–100 in typical cases.

A Study on the Design of an Underwater Distributed Sensor Network for the Shallow Water by An Effectiveness Analysis

ABSTRACT In this paper, we have described the characteristics of the Underwater Distributed Sensor Network (UDSN) and proposed the conceptual design guideline by an effectiveness analysis. To perform the effectiveness analysis, we defined an battlefield environment, and then analyzed principal components which compose the UDSN to find out simulation parameters and system constraints. We have chosen a measure of effectiveness based on a target trajectory, which could enhance intuitive understanding about current status, and performed various simulations to reveal critical design parameters in terms of sensor node types, arrangement, cost and combination of detection information.Key Words : Underwater Distributed Sensor Network(수중분산 센서망), Effectiveness Analysis(효과도 분석), Network Centric Warfare(네트워크 중심전), Surveillance System(감시 체계) 1. 서 론 천해지역에서 잠수함과 같은 위협 세력에 효율적으로 대응하기 위해서는 상시 감시가 가능한 경계 체계 구축이 요구되나, 초계기, 초계함 및 잠수함과 같은 전통적인 유인 플랫폼만으로는 소기의 목적을 달성하기가 쉽지 않다. 이에 미국에서는 수중에 설치된 음향/비 * Corresponding author, E-mail: belfre@add.re.krCopyright