천해수심 적용을 위한 정밀수중항법시스템 설계

Abstract

This paper presents the implementation of precise underwater navigation system using two acoustic ranging sonars for shallow water depth application. Estimation of accurate positions is a key issue to achieve qualified navigation solution used for underwater construction and survey using side scan sonar, multi-beam echo-sounder, scanning imaging sonar, sub-bottom profiler and underwater camera image mosaic. To implement the precise underwater navigation for underwater construction, three strategies are selected. Firstly, absolute positions are estimated by two acoustic ranging sonars. Secondly, outliers due to multi-path reside outside of pre-defined gate are removed and not used in the position estimation algorithm. Thirdly, the geographical land marks such as caisson wall or side valleys identified from the sonar images of forward and backward imaging sonars are compared with the estimated positions to enhance the position accuracy. In this paper, to get absolute ranges, low cost two ranging sonars (sub-system of long base line system) are selected to reduce overall navigation solution cost. Because low cost system cannot measure ranges simultaneously, range R1’ at time t2 should be estimated after measuring R1 at time t1 by using dead-reckoning estimation algorithm. Range R2 can be directly measured at time t2 and the precise vehicle position can be calculated. The performance of developed approach is evaluatsed for underwater construction and survey using side scan sonar, multi-beam echo-sounder, scanning imaging sonar, sub-bottom profiler and underwater camera image mosaic. To implement the precise underwater navigation for underwater construction, three strategies are selected. Firstly, absolute positions are estimated by two acoustic ranging sonars. Secondly, outliers due to multi-path reside outside of pre-defined gate are removed and not used in the position estimation algorithm. Thirdly, the geographical land marks such as caisson wall or side valleys identified from the sonar images of forward and backward imaging sonars are compared with the estimated positions to enhance the position accuracy. In this paper, to get absolute ranges, low cost two ranging sonars (sub-system of long base line system) are selected to reduce overall navigation solution cost. Because low cost system cannot measure ranges simultaneously, range R1’ at time t2 should be estimated after measuring R1 at time t1 by using dead-reckoning estimation algorithm. Range R2 can be directly measured at time t2 and the precise vehicle position can be calculated. The performance of developed approach is evaluat