Sea Technology

MAY 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Ocean Observation With Coordinated Robotic Platforms Coordination Algorithms Maintain Vehicle Formation By Nuno A. Cruz • Bruno M. Ferreira • Aníbal C. Matos T he coordinated operation of marine vehicles has been a particularly active research topic during the last decade, with the realization that the new scenarios for underwater monitoring and intervention require new paradigms of operation, based on heterogeneous robotic assets. In order to exploit their complementary competencies in an effcient way, such operations require the development of robust formation-control strategies and a dependable communications infrastructure to exchange reliable information in a timely manner. When using AUVs, the communications channel is the water, and the formation-control strategy has to encompass the hindrances associated to underwater communications. A long-term program for using multiple heterogeneous vehicles for marine operations is being developed at the Ocean Systems Group at INESC TEC, University of Porto, in Portugal. The overall goal is to integrate a feet of AUVs, autonomous surface vehicles (ASVs) and moored systems. Pres- ent work involves use of the MARES AUV, Zarco and Gama ASVs, and navigation and instrumentation buoys (NIBs). The MARES is a small, torpedo-shaped AUV 1.5 meters long and 32 kilograms in weight in the basic version. In a typical confguration, a PC/104 computational system manages the entire mission, including communications with other devices and a control station. Navigation is provided by the fusion of data from an inertial measurement unit (IMU) and an acoustic system for long baseline localization (LBL), complemented by a small GPS receiver, when the vehicle is at the surface. Four thrusters provide the capability to move as fast as 5 knots and to hover in the water column, with a set of lithium-ion batteries ensuring 10 hours of operation. MARES is a highly modular vehicle, with the ability to integrate a great variety of payload sensors, and it has been operating since 2007, mainly in environmental-monitoring missions. Zarco and Gama are ASVs that use IMU measurements and GPS data to navigate. Their open platforms allow an easy integration of new The MARES AUV. (Top) The Zarco and Gama ASVs. (Middle) Navigation and instrumentation buoys. May 2013 / st 37

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