Development of a LED and GNSS-equipped towed buoy to enhance AUV localization

Modern mobile robots require precise and robust localization and navigation systems to perform their missions correctly. Especially in the underwater environment, where global localization sensors such as the Global Navigation Satellite System (GNSS) cannot be exploited, the development of localization and navigation strategies becomes more challenging.A small towed buoy has been designed and realized to work as interface unit between an Autonomous Underwater Vehicle (AUV) and its control station. A GNSS sensor, installed over the buoy, provides the vehicle with a reliable position measure to be used either to improve its localization accuracy or just as a safety measure flagging whether its localization algorithms are somehow failing. Furthermore, the device enables Wi-Fi communication with the control station while the vehicle is performing its underwater inspection tasks, allowing real-time visualization of the data acquired by payload sensors.The towed buoy is equipped with 4 LEDs placed in square shape structure that can be detected by a camera placed on top of the AUV. A strategy based on the Perpective-n-Point (PnP) problem has been developed to transfer the original GNSS measure of the buoy to the vehicle.The position measure is then used in an Unscented Kalman Filter (UKF) which estimates the vehicle position. The resulting navigation methodology has been validated offline by employing the sensor measurement values logged during past on-field missions of FeelHippo AUV, a lightweight and compact robot developed by the Department of Industrial Engineering of the University of Florence (UNIFI DIEF).