A better way to navigate on deep sea floors

IFREMER-French Institute for Sea Exploration and Exploitation-is currently operating manned submersibles, towed sonars and ROVs down to 6000 m. IFREMER are replacing their positioning system resting on long base line (LBL) by a new positioning system called POSIDONIA which is under development at the company group Thomson Sintra ASM and Mors Environment. This replacement aims to reduce operators time and overall costs by improving accuracy, reliability and flexibility in comparison with the existing systems. To achieve these characteristics, the POSIDONIA positioning system is of a new breed which combines a short base line (SBL) and an ultra short base line (USBL). It has been designed to operate in noisy environments and get rid of multipath effects, to compensate for the lack of precise radio navigation, and generally to comply with the various task requirements. Therefore, not only has the acoustic signal processing been optimized, but also the beacon functionalities to give full versatility. In addition, the need of a high precision vertical and heading reference unit (VHRU), to make up for the vessel attitude, has induced the definition of a hybrid VHRU based on both GPS and inertial sensors.<>