T-CoLoc: Leveraging Tethers for Reliable Co-Localization within an Underwater ROV Chain

Underwater Remotely Operated Vehicles (ROVs) exchange data with a control station via a communication cable. One or more intermediate robots can be placed along this tether to manage its shape and minimize the mechanical effects on the ROV. This work deals with the localization of a pair of underwater robots connected by a tether, in a previously unknown environment. While each robot can estimate its trajectory and a model of its surroundings using Simultaneous Localization And Mapping (SLAM) algorithms, aligning these observations in the same reference frame requires inter-robot data association. In this work, we introduce T-Coloc, a new method for aligning models' frames that leverages an estimation of the tether shape to align individual robot observations. An experimental validation in a pool demonstrates that T-CoLoc can align the trajectories of the two robots in the same reference frame with an error lower than 20 cm using the noisy shape estimation of a 3 m long tether.