Estimation of bearing error of line array sonar system caused by bottom bounced path

해저면 반사신호의 선 배열 소나 방위 오차 해석

Abstract

The Line array sonar consisting of several hydrophones increases array gain and improves the performance for detecting the direction of the target compared to single hydrophone. However, line array sonar produces the bearing error that makes it difficult to determine the bearing of incoming source signal due to the relation between bearing angle of target and vertical angle of multipath signals. Vertical angles of multipath are varied with the geometry of receiver and target and various underwater environments, therefore it is necessary to consider the bearing error to estimate accurately the bearing of the target. In this study, acoustic modelling was performed to understand the effect of multipath signals on the target signal. The errors of bearing angle estimated from the bottom bounced signals are calculated with several environment. In addition, the expected bearing line, as a function of source-receiver range, compensated for the bearing error is predicted from the estimated bearing angle.

선 배열 소나는 배열 이득으로 인해 단일 소나에 비해 상대적으로 음압이 낮은 표적 신호일 경우에도 방위 추정이 가능한 장점이 있다. 하지만 선 배열 소나에서는 표적의 방향을 나타내는 표적 방위각과 음파의 다중경로에서 발생되는 수직각의 영향으로 방위 오차가 발생하며 이로 인해 수신 신호로부터 표적 방위를 추정하는데 어려움이 존재한다. 수중의 음파 전달 환경에 의해 발생하는 다중경로는 각 경로별로 상이한 수직각을 가지므로 이러한 특성이 선배열 소나의 방위 추정에 미치는 영향에 대해 고려할 필요가 있다. 본 논문에서는 선 배열 소나에서 다중경로의 영향으로 인해 발생하게 되는 방위 오차를 확인하며 해저면 반사 경로에서 수직각에 의한 오차를 모의하여 환경에 따른 방위 오차의 차이를 분석한다. 또한 추정된 방위각에서 거리에 따라 방위 오차를 고려한 예상 표적 방위선을 도출한다.

Fig. 1. Schematic representation of target bearing (ϕ), vertical angle (μ) and estimated bearing (θ).

Fig. 2. Relationship between estimated bearing and target bearing as a function of vertical incident angle.

Fig. 3. Eigenray tracing outputs during winter for source-receiver ranges of 5 km (top), 15 km (middle) and 30 km (bottom) in the East Sea.

Fig. 4. Ray tracing outputs of bottom bounced path with sound speed profile, (a) constant SSP (1500 m/s), (b) Munk SSP (minimum sound speed at 400 m).

Fig. 5. Comparisons between the (a) simulation results of bearing error for the isovelocity condition and (b) simulation results of bearing error for the Munk profile.

Fig. 6. Simulation results of bearing errors as a function of depth for the isovelocity condition. The total water depths of experimental site are (a) 500 m, (b) 1500 m, (c) 2500 m, respectively.

Fig. 7. Sound speed profile and bathymetry of the simulation.

Fig. 9. (a) Estimated bearing line along distance from constant target bearing, (b) expected target bearing line along the distance from the constant estimated bearing.

Fig. 8. (a) Example of application of a straight line for the direct path of target signal, (b) example of application of a straight line for the bottom bounced path of target signal.

Fig. 10. Example of application of expected target bearing line along the distance from the constant estimated bearing for bottom bounced paths of the target signal.

Table 1. Bearing errors resulting from incoming signals with different vertical angles.