ROV Localization Using Ballasted Umbilical Equipped With IMUs

This article describes an affordable and setup-friendly cable-based localization technique for underwater remotely operated vehicles, which exploits the piecewise linear shape of the umbilical being equipped with a sliding ballast. Each stretched part of the cable is instrumented with a waterproof inertial measurement unit (IMU) to measure its orientation. Using the cable's geometry, the vehicle's location can be calculated in relation to the fixed or moving end of the cable. Experiments carried out with a robotic system in a water tank prove the reliability of this localization strategy. The study investigates the influence of measurement uncertainties on cable orientation and length, as well as the impact of the IMU location along the cable on localization precision. The accuracy of the localization method is discussed.

I. Introduction

Underwater communication and localization are particularly challenging since global navigation satellite system (GNSS) radio signals are immediately absorbed by water. To replace it, ultrashort baseline (USBL) positioning systems are the most common solution for underwater vehicles geo-localization. These systems rely on an array of acoustic transducers placed under a ship and a transponder installed in the mobile robot. The position of the robot can be estimated with respect to the boat by travel time and phase difference. If needed, the global position of the vehicle can then be deduced by combining the USBL with the GNSS localization of the ship. However, USBL systems are significantly limited in confined environments and shallow water due to the multiple reflections of the acoustic waves they depend on, hence the need for alternative or complementary solutions in these kinds of environments.