Jan Opderbecke

Map based underwater navigation using a multibeam echosounder

This paper describes a navigation system for underwater vehicles (UV) using bathymetric profiles. The UV localisation by matching a local bathymetry within a reference map aims to avoid the use of transponder-based positioning systems which need a costly preparation. Terrain based navigation concerns, using a vehicle-borne multibeam echosounder, to build a local map of the bottom and to match it to a previously constructed terrain map. Bathymetric image restoration and segmentation are necessary before extracting characteristic points from the two maps. These points are matched by the means of rotational and translational invariant attributes. An iterative algorithm estimates the position and the orientation of the local bathymetry and actualizes the set of matched points, The real time estimation of attribute variances allows the use of probabilistic tools like the Mahalanobis distance (threshold) and the Kalman filter (position estimation).

Real-time geo-referenced video mosaicking with the MATISSE system

This paper presents the MATISSE system: Mosaicking Advanced Technologies Integrated in a Single Software Environment. This system aims at producing in-line and off-line geo-referenced video mosaics of seabed given a video input and navigation data. It is based upon several techniques of image and signal processing which have been developed at Ifremer these last years in the fields of image mosaicking, camera self-calibration or correction and estimation of navigation data.

A terrain referenced underwater positioning using sonar bathymetric profiles and multiscale analysis

Terrain-based underwater navigation using sonar bathymetric profiles is presented. It deals with matching high resolution local depth maps against a large, onboard, 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 will focus on partial differential equations based scale-space techniques. This approach is tested using real terrain data of the Var underwater canyon (France).

GREX sea trials: first experiences in multiple underwater vehicle coordination based on acoustic communication

As unmanned marine vehicles rapidly establish themselves as powerful and reliable tools in an ever increasing number of tasks, the focus of research has shifted towards simultaneous operation of coordinated fleets of vehicles. The GREX project joins this development effort with a comprehensive and ambitious development plan. This paper gives account of the first sea trials experience involving a fleet of two AUVs performing a simple coordination task relying on inter-vehicle acoustic communication.

Segmentation of bathymetric profiles and terrain matching for underwater vehicle navigation

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 reference map. The matching algorithm locates the local depth map within the a priori known larger map to determine the absolute position and heading of the vehicle. Two separate approaches for this problem are presented. The first uses a contour-based representation of depth maps. Contours are extracted from both local and reference maps. Invariant attributes under rigid plane transformation are associated with each contour point, so that the problem is reduced to a point-based matching algorithm: given two point sets, find correspondences and estimate transformation between the two sets. We shall particularly focus on the formalism of partial differential equations, which is used to smooth depth maps in a morphologically invariant way and to obtain anisotropic contours. The second approach is also based on a correspondence algorithm. Here, ...

An integrated multiscale approach for terrain referenced underwater navigation

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).

An experimental study of a robust self-calibration method for a single camera

This paper presents a robust self-calibration method as well as results from experiments and simulations. The algorithm tracks points in an image sequence and exploits successive views in order to estimate the fundamental matrix and finally the intrinsic parameters of the camera. In the considered application, the camera is mounted on an underwater vehicle in a vertical position. Taking into account the constraints and the controllability of the underwater vehicles movements, we study the influence and exploitation of these movements for the estimation of the intrinsic parameters. This paper presents the major steps of the robust self calibration algorithm. Starting from a set of matched points that may comprise bad matches, we describe the estimation of the fundamental matrices using a RANSAC algorithm scheme and the computation of the intrinsic parameters. Experiments are explained and a sensible motion for self-calibration is proposed.

Investigation of solar noise impact on the performance of underwater wireless optical communication links

We investigate the effect of environmental noise, caused by solar radiations under water, on the performance of underwater wireless optical communication (UWOC) systems. Presenting an analytical and generic model for this noise, we examine its impact on the link performance in terms of the bit error rate (BER). This study is conducted for different photo-detector types in the aim of highlighting practical limitations of establishing UWOC links in the presence of subsea solar noise. We show how the solar noise can impact the performance of UWOC links for relatively low operation depths. The results we present provide valuable insight for the design of UWOC links, which are likely to be established at relatively low depths. They can be exploited not only for the purpose of practical UWOC system deployment but also for in-pool experimental set-ups, since they elucidate the effect of ambient light on the measurements.

Multiple AUV control in an operational context: a leader - follower approach

As Autonomous Underwater Vehicles universally establish themselves as invaluable tools to provide unprecedented results in a variety of scientific, industrial and naval scenarios, the focus of development is gradually shifting towards considering the operation of multiple cooperating vehicles. There is widespread consensus on that despite the added complexity of having to operate several vehicles, the multiple AUV approach enables the definition of new interesting scenarios which offer a potential improvement in the quality of the collected data and a reduction in operational costs.

Autonomous navigation of the free-swimming vehicle SIRENE

The project DESIBEL, funded by the European Union (MAST-2 programme), included development of the underwater vehicle demonstrator SIRENE. The free-swimming, acoustically, remotely operated vehicle is designed to place and recover deep-sea measuring stations on the sea-floor. The acoustic data link allows one to monitor the vehicle state from the surface and to send guidance commands. The positioning system consists of an acoustic rangemeter working with transponder beacons, and sensors describing attitude and movement of the vehicle. The position estimator realizes two functionalities: 1) to realize selection of consistent sensor measurements; and 2) to compute a position estimate from the validated information. The sensor system as well as the positioning algorithm used are the subjects of this paper. Results from various sea-trials are described and future improvements discussed.