A terrain-based underwater navigation using sonar bathymetric profiles is presented. It deals with matching high resolution local depth maps against a large, on-board, low resolution reference map. The matching algorithm locates the local depth map within the a priori larger map to determine absolute position and heading of the vehicle. It uses cliff maps which are steep gradient contours extracted from both local and reference maps. This segmentation provides us with a means to extract critical points, which are defined as high curvature values. The problem is reduced to a singular point-based matching algorithm: given two point sets, find correspondences and estimate transformation between the two sets. In order to register maps at different scales, a part of this study concentrates on partial differential equations based scale-space techniques. This approach is tested using real terrain data of the Var underwater canyon (France).

Underwater robotic systems require a control architecture that handles automatic control aspects and discrete-event management while considering real-time issues within a formalized framework in order to achieve a high degree of autonomy and robustness while performing missions. To extract generic characteristics of working implementations, we examine two methodologies developed independently by French and American research organizations to control their underwater robots. In particular, we study how a specific reactive and complex mission is encoded under the two different methodologies. Details of the methodologies along with mission programs created by each team to accomplish the evaluation mission are presented.

This paper presents an algorithm which allows an AUV to reset its localization (position and orientation) and to estimate the water current while moving in the vicinity of two acoustic beacons. The algorithm is based on a Kalman filter which integrates the measurements provided by an ultra short base line array located in the vehicle, a Doppler log, a depthmeter and an attitude and heading reference system. After such an estimation phase, the vehicle can start to dead reckon away from the beacons in the best conditions and come back for a reset when necessary. Various considerations about the algorithm allow us to introduce the concept of 'navigation supervisor' currently under development at IFREMER. This study is conducted based on the work previously done for implementation of high-level intelligent control and mission programming.

This paper investigates the benefits of applying simple PID+nonlinear controller to subsea robot. This control structure has the advantage of only adding a supplementary nonlinear feedback loop to the existing linear PID-regulator and at the same time improving both the transient and stability margins. Several simulations and experiments have been performed on the experimental subsea robot (VORTEX) and have demonstrated the improvements of the PID+nonlinear controller over the simple PID.>

Computer assistance for the manned guidance of ROVs (remotely operated vehicles) is studied. In this approach, it is possible to estimate an optimal location by fusing data deriving from log and gyroscope or a nonoptimal location by composition of compass, depthmeter, and log data. This relative reckoning is achieved by taking into account a hypothesis on the value of the undercurrent. Therefore, a second reckoning module model is proposed to improve the ROV position close to an offshore jacket, fusing data given by an echo-sounder belt and taking into account a CAD map of the surroundings. This new estimate is independent of the undercurrent, and it is possible with the help of the operator to match this absolute model with the relative one in an asynchronous way. This matching gives a new hypothesis on the value of the undercurrent and resets the dead-reckoning module.>