Vision-Based Water Clearance Determination in Maritime Environment

Determining the distances from the hull of the own ship to obstacles or land, i.e. water clearance, is a fundamental task in navigation. This is particularly relevant during maneuvering in the harbor or navigating in confined waters. We introduce the concepts of area water clearance and line water clearance. Area water clearance is important especially for path planning and obstacle avoidance. Line water clearance is critical for maneuvering when approaching the quay. In this work, we present a vision-based approach to deter- mine the water clearance. A single calibrated camera together with a semantic segmentation network is used to detect the water region in an image, and back-projection to determine the water clearance on the sea surface in world units. We validate the proposed approach on real data collected from two distinct vessels, where the proposed method is able to produce reliable water clearance for distances beyond one kilometer. During harbor maneuvering 90% of the relative water clearance errors were found to be between −2.3% and 3%.