No abstract

Accurate time synchronization of the nodes of digital underwater acoustic (UWA) networks is necessary for the effective use of information obtained from various kinds of underwater sensors over a vast water area. The sensors of autonomous underwater vehicles (AUV) are widely used to address new challenges. One of them is time synchronization of sensors on mobile carriers, as well as synchronization of the clocks on mobile nodes of UWA networks, for example, teams of AUVs that perform coordinated and/or cooperated operations. The paper presents theresults of the experiments on using UWA modems for AUV positioning, namely, UWA modems with chip-scale atomic clocks (CSAC) that allow accurate measurements of delays in propagation of UWA signals and, thus, accurate estimation of ranges to their georeferenced sources. In addition, the accuracy of CSAC operation in various situations as well as positioning accuracy of AUVs having UWA modems with integrated CSACs are analyzed based on the experimental results. Also given are practical recommendations on how to "discipline" (steer) CSACs and provide their phase synchronization with a source of timekeeping signals.

No abstract

The MORPH project (FP 7, 2012‐2016) is aimed at developing efficient methods and tools to map the underwater environment in situations that are not easily addressed by current technology. Namely, the missions that are of interest are those that involve underwater surveying and marine habitat mapping of rugged terrain and structures with full 3D complexity, including vertical cliffs. Potential applications include the study of cold water coral reef communities, ecosystems from underwater canyons, pipeline and harbor monitoring, or the inspection of wind turbine foundations. The project introduced and advanced a novel concept of an underwater robotic system composed of a number of mobile robot modules (nodes), carrying complementary sensors for perception of the environment. Instead of being physically coupled, the modules are connected via communication links that allow a flow of essential information among them. Without rigid links, the so-called MORPH Supra-Vehicle can reconfigure itself and adapt according to the environment and mission goals, responding, for example, to the shape of the terrain, including vertical walls. The flexibility allows for more optimal positioning of each sensor, increased number of simultaneous viewpoints, and generally high-resolution data collection.MORPH is aimed at providing a proof-of-concept demonstration of such capabilities, an effort that includes technological developments in many of the subfields of underwater technology. The main results are summarized and presented in this paper.<def-list>Abbreviation List<def-item><term>AUV</term><def>autonomous underwater vehicles</def></def-item><def-item><term>CV</term><def>camera vehicle</def></def-item><def-item><term>CWC</term><def>cold water corals</def></def-item><def-item><term>GCV</term><def>global navigation and communications vehicle</def></def-item><def-item><term>ICP</term><def>iterative closest point method</def></def-item><def-item><term>LSV</term><def>local sonar vehicle</def></def-item><def-item><term>MBES</term><def>multibeam echosounder</def></def-item><def-item><term>MCL</term><def>mission control language</def></def-item><def-item><term>PF</term><def>path following</def> </def-item><def-item><term>PI</term><def>principal investigator</def></def-item><def-item><term>ROF</term><def> range-only formation</def></def-item><def-item><term>ROS</term><def>Robot Operation System</def></def-item><def-item><term>SSV</term><def>surface support vessel</def></def-item> <def-item> <term>TDMA</term> <def> time division multiple access </def> </def-item><def-item><term>USBL</term><def>ultra-short baseline (navigation)</def></def-item> <def-item> <term>UUV</term> <def> unmanned underwater vehicle </def> </def-item><def-item><term>VCS</term><def>version control system</def></def-item></def-list>

No abstract