THESIS

Tali Hurtós defends her PhD thesis: “Forward-Looking Sonar Mosaicing for Underwater Environments”

Vehicle operations in underwater environments are frequently compromised by poor visibility conditions. The perception range of optical devices is heavily constrained in turbid waters, thus often complicating navigation and mapping tasks in environments such as harbors, bays, or rivers. A new generation of high-frequency forward-looking sonars that provide acoustic imagery at near-video frame rates have recently emerged as a promising alternative for working under these challenging conditions. In this thesis, we propose an end-to-end mosaicing framework tailored to the characteristics of forward-looking sonar imagery in order to build consistent overviews of planar underwater areas regardless of water visibility. Our solution targets versatility: it enables the generation of acoustic mosaics that involve roto-translational motions and comprise different vehicle tracklines; it is suitable for a wide range of scenarios, from feature-rich areas to environments with scarcity of features; it can be applicable on data collected with minimally instrumented vehicles; and it allows...
3D mapping

Ricard Campos defends his PhD thesis “Surface Reconstruction Methods for Seafloor Modelling”

Underwater maps are an important source of information for the scientific community, since mapping the seafloor is the starting point for underwater exploration. The advance of range scanning methodologies, both using acoustic and optical techniques, enables the mapping of the seabed to attain increasingly larger resolutions. However, all these techniques sample the surface to reconstruct in the form of a point cloud. For the case of areas containing non-trivial 3D relief, achieving a continuous representation from this discrete sampling is a complex task. Surface reconstruction methods try to tackle this problem by recovering a continuous surface representing the object in the form of a mesh of triangles, easing visualization and further processing. This thesis proposes four different strategies to tackle the problem of surface reconstruction from point sets. We start by reviewing the state of the art on surface reconstruction methods. From this survey, we extract some conclusions regarding the…

Angelos Pdh

Angelos Mallios defends his PhD Thesis “Sonar Scan Matching for Simultaneous Localization and Mapping in Confined Underwater Environments”

This thesis presents the development of a localization and mapping algorithm for an autonomous underwater vehicle (AUV). It is based on probabilistic scan matching of raw sonar scans within a pose-based simultaneous localization and mapping (SLAM) framework.   To address the motion-induced distortions affecting the generation of full sector scans, an extended Kalman filter (EKF) is used to estimate the robot motion during that scan. The filter uses a constant velocity model with acceleration noise for motion prediction.Velocities from Doppler velocity log (DVL) and heading measurements from attitude and heading reference system (AHRS) are fed asynchronously and update the state. The scan is undistorted by compounding the relative robot position in the scan, with the range and bearing measurements of the beams gathered by the sonar. Assuming Gaussian noise, the algorithm is able to estimate the uncertainty of the sonar measurements with respect to a frame located at the center…

phd-galceran

Coverage Path Planning for Autonomous Underwater Vehicles

Doctoral thesis “Coverage Path Planning for Autonomous Underwater Vehicles” By Enric Galceran, PhD student of the Doctoral Program in Technology Supervised by Dr. Marc Carreras Pérez   Abstract At present, a mission to survey the ocean floor with an Autonomous Underwater Vehicle (AUV) is typically planned by selecting a list of waypoints that then the vehicle will automatically navigate through while keeping a safe distance from the bottom. Nonetheless, this approach has major drawbacks: (1) it does not allow the vehicle to safely operate amidst protrusions on the sea floor; (2) when traversing rugged terrain, the vehicle is forced to keep a conservative altitude, limiting applications  requiring close proximity such as photomosaicing; (3) when inspecting 3D, protruding structures from the bottom the vehicle can only perceive them from an overhead viewpoint, resulting in poor data collected from these sites; (4) it does not account for the effect of the terrain…

ASM

Automated underwater object classification using optical imagery

PhD Thesis “Automated underwater object classification using optical imagery” By Shihavuddin, A.S.M Supervised by Dr. Nuno Grácias, Dr. Rafael García   Abstract This thesis addresses the problem of automated underwater optical image characterization. Remote underwater optical sensing allows the collection and storage of vast amounts of data for which manual classification may take months. Supervised automated classification of such datasets can save time and resources and can also enable extraction of valuable information related to marine and geological research.