A Study on Target Echo Analysis and Target State Estimation for an Active SONAR


In order to develope underwater guidance weapon system with an excellent detection performance, precise analysis and modeling on underwater acoustic environment and target echo must be precede. Performance prediction and optimization of detection parameters can be possible by simulation based on a precise modeling. A study on underwater acoustic environment and target echo is performed by both the numerical modeling method based on theory and the analytical method based on analyzing the acoustic data acquired on laboratory and sea test. Experiment for such an acoustic approach can be classified into scaled target experiment and sea experiment. Data acquisition by means of a scaled target experiment can be performed using smaller budget and less effect comparing with a sea experiment. Also, a scaled target experiment has merits on precise controlling of target aspect and acquisiting of target echo with good signal to noise ratio. This experiment is necessary to clarify the relationship between target echo and transmitting pulse such as coating effect and inner structure effect of a target, and designing transmitting pulse depending on a target. Data acquisition in the state of precise target aspect makes a study on target echo possible. This paper is important on the fact that two major research topics in the field of target acoustic, target echo modelling(forward model) and target state estimation technique(inverse model), are developed and verified. Target echo modeling simulates target echo using the selected model parameters, and is a kind of forward modeling. On the other hand, TSE technique estimates important target parameters using the recoded target echo, and is a kind of inverse or parameter estimation technique. A study on target echo analysis classifies target echo into 4 components based on outer and inner structure such as specular reflection, acoustic diffraction, elastic scattering, and multiple scattering. Through the theoretical studies, these 4 components are separated into moving HL and fixed HL depending on each characteristics, and are applied to target echo model. Also, using the developed HL resolving algorithm, target highlight position is precisely estimated and theory is verified by resolving target echo into each component using the data, recoded on scaled target experiment. Target echo model developed through theoretical study and verification improve reliance of simulation used in developing underwater guidance weapon system. For verification of the TSE algorithm, we analyze the errors of TSE using the target echo model as a function of target aspect angle and resolution. Based on the analysis of TSE error, we gave a limitation of the algorithm. The second topic of this paper is result on selecting SONAR designing parameters which maximize SONAR performance. Detecting performance of a SONAR priority determined by hardware performance such as transmitting power, beam pattern, and receiving sensitivity. However, the components, next predetermined hardware, which determine the detecting performance are SONAR operating and detecting parameter. Primarily, target strength is the most important parameter among target detecting parameters. In the case of studying target characteristics, this parameter easily considered as depending on target itself. On other hand, in the side of active SONAR detecting performance, this parameter varies on the transmitting pulse length, pulse type, and detection algorithm. Conditions to improve target strength are studied. Next, TSE algorithm is to resolve highlights and to estimate spatial position of each highlight. In this case, the temporal resolution becomes important performance. In this algorithm, signal is processed using the matched filter. HL resolution(temporal resolution) of this algorithm is proposed and verified using result, from simulated signal and scaled target experiment. Also, the fact, that HL resolution changes according to the degree of window overlapping which is decided by hardware computing speed, is verified. HL resolution of a system can be estimated using two resolution limitsresolution limits by algorithm and computing speed. In the last, the concept of processing gain, which is algorithm effect in SONAR equation used to estimate SONAR performance, is proposed and computed. Processing gain is estimated using signal model and is varied with the degree of window overlapping which decided by hardware computing speed. Processing gain can be obtained maximum 18dB by using a matched filter, and can be minus depending on the degree of window overlapping and the time of target echo. The listed results of this paper can be applied to TSE algorithm and ACCM logic for an underwater guidance weapon system. In the future, these results can be applied to techniques for target identification, anti-torpedo torpedo, and stealth as a core technique.Abstract i 목차 iv List of Figures vii List of Tables xiii List of Abbreviations xiv 1. 서 론 1 1.1 표적 음향 연구 개요 1 1.2 축소 표적시험 및 연구의 필요성 4 1.3 연구 동향 5 1.4 연구 내용 6 2. 표적의 반향음 이론 8 2.1 음향산란영역에 대한 산란이론 8 2.2 표적의 반향음 9 2.3 표적의 반향음 성분 10 2.3.1 거울면 반사 10 2.3.2 음향 회절 16 2.3.3 탄성 산란 15 2.3.4 다중 산란 18 2.4 표적 반향음 합성 21 3. 표적의 상태 추정 이론 23 3.1 표적의 상태 추정 23 3.2 정합 필터 24 3.2.1 CW 신호에 대한 모호함수 27 3.2.2 LFM 신호에 대한 모호함수 29 3.3 방위 추정 31 3.4 공변 행렬을 이용한 표적의 상태 추정 35 3.5 HL를 이용한 표적 상태 추정시 오차 발생 요소 36 4. 축소 표적 시험 및 결과 분석 38 4.1 축소 표적 시험 38 4.1.1 축소표적 시험 장비 38 4.1.2 축소표적 시험 내용 47 4.2 축소 표적 시험 결과를 이용한 반향음 분석 48 4.2.1 CW 신호를 이용한 반향음 분석 48 4.2.2 LFM 신호 분석 프로그램 53 4.2.3 LFM 신호를 이용한 반향음 분석 55 4.3 축소 표적 시험을 이용한 표적의 상태 추정 62 4.3.1 표적의 상태 추정 결과 62 4.3.2 분해능에 따른 표적의 상태 추정 결과 69 5. 소나의 성능 향상을 위한 변수 설정 72 5.1 표적 강도에 따른 펄스 길이 설계 72 5.1.1 표적강도 72 5.1.2 축소표적의 표적강도 측정 78 5.2 HL 분해능 81 5.2.1 TSE 알고리즘 분해능의 이론적 한계 81 5.2.2 축소표적신호에 대한 분해능 85 5.2.3 윈도우 겹침에 따른 분해능 92 5.3 정합 필터의 연산 이득 94 5.3.1 연산이득 정의 94 5.3.2 신호 모델 및 시뮬레이션 결과 96 5.3.3 윈도우 겹침에 따른 연산이득의 변화 97 6. 결론 103 6.1 표적 반향음 연구 및 표적 상태 추정 103 6.2 소나 성능 향상을 위한 변수 설정 104 7. 참고 문헌 106 부록 1. 표적 형상에 의한 표적 반사 계수 110 부록 2. LFM 신호의 시간 함수 114 부록 3. 표적 종류에 대한 CW 신호 분석 그림 116 부록 4. 연산이득이 포함된 소나방정식 12

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This paper was published in 한국해양대학교(KMOU).

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