Distance measurement system based on image sensors for automatic berthing of ships

This paper describes a distance measurement system based on image sensors for automatic berthing of ships. An automatic berthing system is a solution to relieve psychological and physical strains on the operator in berthing maneuvering that is the most difficult and delicate phase. Usually, a sensor system for the automatic berthing system should accommodate ship movements such as rolling, pitching, and yawing, in order to continuously measure the relative distance from the ship to a dock in a port. For acquiring the accommodation to the ship movements, the proposed measurement system is composed of two movable image sensors, and measures the relative distance by detecting and tracking a target on the dock. Additionally, a template matching method robust to light fluctuation in outdoor environment, named the vector code correlation, is employed to the movable image sensor for the target detection. From the experimental results performed in an outdoor environment where lighting condition was varied, we confirmed that the measurement system could continuously measure the relative distance under 3.1m of absolute errors in the measuring range of 100m to 5m. Especially, high accuracy within ±1.0m was accomplished from 40m to 5m of the relative distance.