Autonomous Minibuoy Prototype for a Coordinated, Wireless Networked, Ocean-Surface-Sensor Array

We report the design, prototype construction and initial testing of a small minibuoy that is aimed at use in a coordinated, wireless networked array of buoys for ocean surface sensing, both above and below the surface. This vehicle is designed to fill the gap between larger ocean surface vessels and/or moored buoys and subsurface gliders. The size and cost is low enough that these versatile sensor platforms can be deployed easily and in quantity. Since these minibuoys are mobile, they can keep station in currents as large as 25 cm/s or move as an adaptive, coordinated sensor array for high resolution in both time and space. The buoy is about 29 inches (74 cm) long, 16 inches (41 cm) wide (maximum) and weighs about 32 pounds (14.5 kg); hence, it can be deployed easily from small craft. Deployment times are estimated to be one or two days or more depending on propulsion requirements and battery pack -longer with solar power. The buoy structure is fiberglass and PVC with two 2 W electric motors. Control is affected by GPS and magnetic heading sensors and a PID scheme to maintain heading and required speed. Communication is via a 900 MHz system with a range of a km or two with plans for a longer range HF/VHF or satellite system. The initial sensor system is designed for ocean hyperspectral observations as surface truth for an airborne system calibration and validation as well as other ocean color applications. Acoustic, wave, air & water temperature sensors as well as GPS are included. The Mark I prototype has been successfully tested in a pool with manual control of movement.