*Article* **Chemical Spill Encircling Using a Quadrotor and Autonomous Surface Vehicles: A Distributed Cooperative Approach**

**Marcelo Jacinto \*, Rita Cunha and António Pascoal**

Laboratory of Robotics and Systems in Engineering and Science (LARSyS), Instituto Superior Técnico, University of Lisbon, 1049-001 Lisboa, Portugal; rita@isr.tecnico.ulisboa.pt (R.C.); antonio@isr.tecnico.ulisboa.pt (A.P.)

**\*** Correspondence: marcelo.jacinto@tecnico.ulisboa.pt

**Abstract:** This article addresses the problem of formation control of a quadrotor and one (or more) marine vehicles operating at the surface of the water with the end goal of encircling the boundary of a chemical spill, enabling such vehicles to carry and release chemical dispersants used during ocean cleanup missions to break up oil molecules. Firstly, the mathematical models of the Medusa class of marine robots and quadrotor aircrafts are introduced, followed by the design of single vehicle motion controllers that allow these vehicles to follow a parameterised path individually using Lyapunovbased techniques. At a second stage, a distributed controller using event-triggered communications is introduced, enabling the vehicles to perform cooperative path following missions according to a pre-defined geometric formation. In the next step, a real-time path planning algorithm is developed that makes use of a camera sensor, installed on-board the quadrotor. This sensor enables the detection in the image of which pixels encode parts of a chemical spill boundary and use them to generate and update, in real time, a set of smooth B-spline-based paths for all the vehicles to follow cooperatively. The performance of the complete system is evaluated by resorting to 3-D simulation software, making it possible to visually simulate a chemical spill. Results from real water trials are also provided for parts of the system, where two Medusa vehicles are required to perform a static lawn-mowing path following mission cooperatively at the surface of the water.

**Keywords:** quadrotor control; autonomous surface vehicle control; cooperative path following; online path planning; chemical spill boundary encircling
