Showing papers on "iRobot Seaglider published in 2018"

Annual cycle of turbulent dissipation estimated from Seagliders

Abstract: The rate of dissipation of turbulent kinetic energy is estimated using Seaglider observations of vertical water velocity in the mid‐latitude North Atlantic. This estimate is based on the large‐eddy method (LEM), allowing the use of measurements of turbulent energy at large scales O(1–10 m) to diagnose the rate of energy dissipated through viscous processes at scales O(1 mm). The Seaglider data considered here was obtained in a region of high stratification (1 × 10−4 < N < 1 × 10−2 s−1), where previous implementations of this method fail. The LEM is generalized to high‐stratification by high‐pass filtering vertical velocity with a cut‐off dependent on the local buoyancy frequency, producing a year‐long time series of dissipation rate spanning the uppermost 1000 m with sub‐daily resolution. This is compared to the dissipation rate estimated from a moored 600 kHz Acoustic Doppler Current Profiler. The variability of the Seaglider‐based dissipation correlates with one‐dimensional scalings of wind and buoyancy driven mixed‐layer turbulence.

Autonomous Sampling of Ocean Submesoscale Fronts with Ocean Gliders and Numerical Model Forecasting

Abstract: Submesoscale fronts arising from mesoscale stirring are ubiquitous in the ocean and have a strong impact on upper-ocean dynamics. This work presents a method for optimizing the sampling of ocean fronts with autonomous vehicles at meso- and submesoscales, based on a combination of numerical forecast and autonomous planning. This method uses a 48-h forecast from a real-time high-resolution data-assimilative primitive equation ocean model, feature detection techniques, and a planner that controls the observing platform. The method is tested in Monterey Bay, off the coast of California, during a 9-day experiment focused on sampling subsurface thermohaline-compensated structures using a Seaglider as the ocean observing platform. Based on model estimations, the sampling “gain,” defined as the magnitude of isopycnal tracer variability sampled, is 50% larger in the feature-chasing case with respect to a non-feature-tracking scenario. The ability of the model to reproduce, in space and time, thermohaline submesoscale features is evaluated by quantitatively comparing the model and glider results. The model reproduces the vertical (~50–200 m thick) and lateral (~5–20 km) scales of subsurface subducting fronts and near-bottom features observed in the glider data. The differences between model and glider data are, in part, attributed to the selected glider optimal interpolation parameters and to uncertainties in the forecasting of the location of the structures. This method can be exported to any place in the ocean where high-resolution data-assimilative model output is available, and it allows for the incorporation of multiple observing platforms.

Oculus Coastal Glider : A New Shallow-water Oceanographic Glider

Abstract: A new autonomous, underwater glider is presented that uses core technology from the University of Washington gliders and features a novel buoyancy engine for coastal profiling. This free-swimming, self-contained, 74 kg instrument is a companion to the 1000 m Seaglider and the 6000 m Deepglider, and was developed in partnership with NOAA's Pacific Marine Environmental Laboratory. The Oculus Coastal Glider is specifically designed for shallow water operation $( < 200\mathrm {m})$ to meet NOAA observing requirements in the US Arctic by using a new buoyancy engine based on a hydraulic amplifier. The sensor suite on this initial deployment included conductivity-temperature-depth, photosynthetically active radiation, dissolved oxygen, chlorophyll a fluorescence, colored dissolved organic matter, and backscatter. The Oculus Coastal Glider also has a new modular architecture that allows easy expansion to carry larger and higher power sensors in dedicated hull sections. We present the results of laboratory testing of the buoyancy system, system field testing in a fresh water lake (50 m), Puget Sound (200 m), and an initial science mission in the Bering Sea (70 m).

Incorporating real-time acoustic ranging and glider-based Doppler measurements to aid vehicle navigation

Abstract: In the summer of 2017, two Seagliders equipped with low frequency acoustic recorders and 1 MHz acoustic Doppler current profilers (ADCPs) were deployed in the Canada Basin as part of a large-scale acoustic tomography experiment. Acoustic tomography sources were moored at approximately 175 m depth within an acoustic duct enabling acoustic transmission to be received at long ranges. The sources transmitted at a center frequency of approximately 250 Hz every four hours, and ranges between the sources and Seaglider were estimated in real time using a WHOI MicroModem. These ranges can be incorporated into an extended Kalman filter for navigation. In addition, glider-mounted upward-looking ADCPs recorded ~26.5 m shear profiles every 15 seconds. These overlapping profiles can be used to estimate (in post-processing) both the local current profile on a per-dive basis and the glider's relative velocity through the water. In real time, the close-range ADCP velocity measurements can be used to estimate the glider's relative (Through The Water, TTW) velocity to improve the glider's subsea position estimate. We will describe our recent developments in using these Doppler measurements to aid glider navigation, comparing the results to previous developments in range-aided navigation.In the summer of 2017, two Seagliders equipped with low frequency acoustic recorders and 1 MHz acoustic Doppler current profilers (ADCPs) were deployed in the Canada Basin as part of a large-scale acoustic tomography experiment. Acoustic tomography sources were moored at approximately 175 m depth within an acoustic duct enabling acoustic transmission to be received at long ranges. The sources transmitted at a center frequency of approximately 250 Hz every four hours, and ranges between the sources and Seaglider were estimated in real time using a WHOI MicroModem. These ranges can be incorporated into an extended Kalman filter for navigation. In addition, glider-mounted upward-looking ADCPs recorded ~26.5 m shear profiles every 15 seconds. These overlapping profiles can be used to estimate (in post-processing) both the local current profile on a per-dive basis and the glider's relative velocity through the water. In real time, the close-range ADCP velocity measurements can be used to estimate the glider's ...

Seaglider Surveys at Ocean Station Papa: Bin-Averaged Profiles, Currents, and Independent Oxygen Data

Abstract: RELATED CODE (RECOMMENDED): A MATLAB script, "OSP_SG_surveys_bin_data_load_and_plot.m", is available at github.com/noelpelland/SG-at-OSP/. This script provides examples of how to load and manipulate the data in this archive in MATLAB. The script also uses the data to reproduce some selected figures from Pelland et al. [2016] and Pelland et al. [submitted].