1. Groupe de Géosciences Marines, IPGP, CNRS; Case 89, 4 Place Jussieu,; F-75252; Paris; France
2. Computer Vision and Robotics Group, Department of Electronics, Informatics and Automation; University of Girona, Campus Montilivi; E-17071; Girona; Spain
3. Department of Geology and Geophysics; Woods Hole Oceanographic Institution; Woods Hole; Massachusetts; 02543; USA
4. COGIT; Institut Géographique National; F-94165; Saint Mandé; France