Jason I. Gobat

Acoustic navigation and communication for High‐Latitude Ocean Research Workshop

Recent community reports on autonomous platforms and Arctic observing [U.S. National Science Foundation, 2002; Proshutinsky et al., 2004; Rudnick and Perry, 2003] identify the development of under-ice navigation and telemetry technologies as one of the critical factors limiting the scope of high-latitude measurement efforts. Advances in autonomous platforms (profiling floats, drifters, long-range gliders, and propeller-driven vehicles) promise to revolutionize ocean observations, providing unprecedented spatial and temporal resolution for both short-duration process studies and multiyear efforts designed to quantify long-timescale environmental changes. This new generation of platforms facilitates access to logistically difficult regions where weather and remoteness challenge conventional techniques, making them attractive for polar regions. These platforms could provide persistent, high-resolution, basin-wide sampling in ice-covered regions and operate near the critical ice-water interface.

Preliminary results in under-ice acoustic navigation for seagliders in Davis Strait

This paper presents an under-ice acoustic navigation system developed for Seaglider, a buoyancy-driven autonomous underwater vehicle (AUV), and post-processed navigation results from one of fourteen glider deployments between 2006 and 2014 in Davis Strait. Seagliders typically receive all geolocation information from global positioning system (GPS) signals received while they are at the surface, and perform dead reckoning while underwater. Extended under-ice deployments, where access to GPS is denied due to the inability of the glider to surface, require an alternative source of geolocation information. In the deployments described herein, geolocation information is provided by range measurements from mooring-mounted acoustic navigation sources at fixed, known locations. In this paper we describe the navigation system used in Davis Strait and present navigation results from a six degree-of-freedom Kalman filter using post-processed navigation data.

Using gliders to study a phytoplankton bloom in the Ross Sea, antarctica

Over the last several decades, numerous approaches have been used to observe the rapid development of the annual phytoplankton bloom in the Ross Sea, including ship-based sampling, moored instrumentation, satellite images, and computer modeling efforts. In the Austral Spring of 2010, our group deployed a pair of iRobot Seagliders equipped with fluorometers, oxygen sensors and CTDs in order to obtain data on this phenomenon over the entire duration of the bloom. Data from these deployments will be used, along with samples from the recovery cruise and satellite data, to model and better understand the dynamics of this phytoplankton bloom.

Design and Performance of a Horizontal Mooring for Upper-Ocean Research

Abstract This paper describes the design and performance of a two-dimensional moored array for sampling horizontal variability in the upper ocean. The mooring was deployed in Massachusetts Bay in a water depth of 84 m for the purpose of measuring the horizontal structure of internal waves. The mooring was instrumented with three acoustic current meters (ACMs) spaced along a 170-m horizontal cable that was stretched between two subsurface buoys 20 m below the sea surface. Five 25-m-long vertical instrument strings were suspended from the horizontal cable. A bottom-mounted acoustic Doppler current profiler (ADCP) was deployed nearby to measure the current velocity throughout the water column. Pressure sensors mounted on the subsurface buoys and the vertical instrument strings were used to measure the vertical displacements of the array in response to the currents. Measurements from the ACMs and the ADCP were used to construct time-dependent, two-dimensional current fields. The current fields were used as in...

Towards real-time under-ice acoustic navigation at mesoscale ranges

This paper describes an acoustic navigation system that provides mesoscale coverage (hundreds of kilometers) under the ice and presents results from the first multi-month deployment in the Arctic. The hardware consists of ice-tethered acoustic navigation beacons transmitting at 900 Hz that broadcast their latitude and longitude plus several bytes of optional control data. The real-time under-ice navigation algorithm, based on a Kalman filter, uses time-of-flight measurements from these sources to simultaneously estimate vehicle position and depth-averaged local currents. The algorithm described herein was implemented on Seagliders, a type of autonomous underwater glider (AUG), but the underlying theory is applicable to other autonomous underwater vehicles (AUVs). As part of an extensive field campaign from March to September 2014, eleven acoustic sources and four Seagliders were deployed to monitor the seasonal melt of the marginal ice zone (MIZ) in the Beaufort and northern Chukchi Seas. Beacon-to-beacon performance was excellent due to a sound duct at 100 m depth where the transmitters were positioned; the travel-time error at 200 km has a standard deviation of 40 m when sound-speed is known, and ranges in excess of 400 km were obtained. Results with the Seagliders, which were not regularly within the duct, showed reliable acoustic ranges up to 100 km and more sparse but repeatable range measurements to over 400 km. Navigation results are reported for the real-time algorithm run in post-processing mode, using data from a 295-hour segment with significant time spent under ice.

Ocean gliders as tools for acoustic tomography

Ocean gliders are capable and increasingly ubiquitous platforms for collecting oceanographic data such as temperature and salinity measurements. These data alone are useful for ocean acoustic tomography applications, but gliders equipped with acoustic receivers can also record transmissions from acoustic sources, potentially providing additional paths for tomographic inversions. There are challenges associated with the use of gliders as tomography receivers, however, notably the uncertainty in underwater glider position, which can lead to ambiguity between sound-speed and glider position. Glider-based acoustic receptions from moored tomography sources can provide range measurements to aid in subsea glider localization. These data can be used in post-processing for precise glider positioning and in real-time for glider navigation. The current state of the art will be reviewed, and preliminary results will be presented from an experiment in the Arctic Ocean, which seeks to use moored acoustic tomography sou...

Acoustic navigation and communications for high latitude ocean research (ANCHOR)

Recent community reports on autonomous and Lagrangian platforms and Arctic observing identify the development of under‐ice navigation and telemetry technologies as one of the critical factors limiting the scope of autonomous (e.g. floats, AUVs and gliders) high‐latitude measurement efforts. These platforms could provide persistent, high‐resolution, basin‐wide sampling in ice‐covered regions and collect measurements near the critical ice‐water interface. Motivated by the dramatic advances in temporal and spatial reach promised by autonomous sampling and by the need to coordinate nascent efforts to develop navigation and communication system components, an international group of acousticians, platform developers, high‐latitude oceanographers and marine mammal researchers gathered in Seattle, U.S.A. from 27 February ‐ 1 March for an NSF Office of Polar Programs sponsored Acoustic Navigation and Communication for High‐latitude Ocean Research workshop. Workshop participants summarized the current state of know...

NUMERICAL SIMULATION OF THE DEPLOYMENT OF A HYBRID ROV OPTICAL FIBER TETHER

This paper describes a numerical code for simulating the dynamics of an unmanned, underwater vehicle system that is self-propelled and tethered to a surface ship through an optical fiber tether. The vehicle, called a hybrid ROV, uses a buffered, single-mode optical fiber with a maximum working load of 1.7 N for communication and data transmission. The vehicle is designed to go to the deepest parts of the ocean and for exploring beneath the Arctic ice cap. The optical fiber tether is stored in a pair of canisters, one mounted on the vehicle and one mounted on a garage that is lowered from the ship. The canisters each hold 20 km of fiber, which is pulled out during operations when the tension at the canister reaches a threshold value, which is set to the maximum working load of the fiber. The numerical simulation is based on the two-dimensional version of WHOI Cable, a finite-difference solver of the cable equations that includes bending stiffness to model low-tension effects. A velocity/tension based payout algorithm was incorporated into the code to model the behavior of the canisters. In the payout model, the payout velocity is set equal to zero below the threshold tension and varies linearly with tension above the threshold value up to a maximum pay out velocity. Hydrodynamic drag models for axial and normal fluid loading, whose values are a function of Reynolds number, are used to calculate local drag coefficients of the optical fiber. Examples of the vehicle being lowered to the sea bottom in uniform and shear currents are used to demonstrate the capabilities of the code and the performance of the tether and payout system.

Long-term evolution of the coupled boundary layers (STRATUS) mooring recovery and deployment cruise report NOAA Research Vessel R H Brown • cruise RB-01-08 9 October - 25 October 2001

Funding was provided by the National Oceanic and Atmospheric Administration under Grant Numbers NA96GPO429 and NA17RJ1223.