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Figure 1 The Wave-Glider ready for deployment at AIMS. Image credit: Scott Bainbridge, AIMS

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The Liquid Robotics’ Wave Glider – a multi-purpose platform for ocean and shelf observations – lessons from the Great Barrier Reef.

Wave Gliders, wave powered autonomous surface robots, are a proven ocean surface observing platform but their use in shallower complex reef and shelf environments is largely untested.

The Australian Institute of Marine Science (AIMS), as part of the Q-IMOS Node, deployed a Liquid Robotics Wave Glider in the central Great Barrier Reef (GBR) and undertook a series of tests to simulate transect based data, such as currently obtained from underway vessels and, via station keeping mode, the ability of the platform to provide data equivalent to a fixed mooring.

The Wave Glider provided real time data every 10 minutes along 200nm of between reef transects over seven days collecting oceanographic data which was validated against a fixed wave-rider buoy and the Yongala NRS.

The Wave Glider represents a unique platform for shallow reef and shelf environments due to:

  • low (effectively zero) operational cost once deployed;
  • long deployment cycle (months);
  • the ability to re-task the platform or adaptively sample based on observed events or mission priorities;
  • use of standard oceanographic instruments and methods, and;
  • continuous position information and abundant power.

The results show that the Wave Glider is able to perform as well as underway vessel based observations and provides a good representation of static mooring based surface observations. The platform is operationally proven and represents a level of technology and operational readiness that makes it suitable for routine coastal and shelf based IMOS missions.

The Liquid Robotics Wave Glider platform has proven itself as an ocean observing platform but what is less understood is its ability to operate in shallow complex environments, such as around reefs, and its ability to collect data equivalent to existing IMOS collection methods, such as from underway vessels and fixed moorings.

AIMS, with Boeing, Liquid Robotics and the Queensland Department of Science, Information Technology and Innovation (DSITI), set out to test the utility of the Wave Glider platform for a range of inshore and cross-shelf tasks in the central Great Barrier Reef in September 2017, covering 200nm within the reef matrix.

The platform, using waves and a solar powered thruster, averaged 1.4 knots over the seven day mission. The platform can run in autonomous mode where it transits autonomously from way-point to way-point or it can be remotely piloted. Either mode allows for the glider to be remotely re-tasked and re-directed based on evolving mission requirements or in response to events detected.

For this mission the Wave Glider, via configurable payload bays, carried a SeaBird CTD with a DO sensor, Teledyne 600KHz ADCP, Liquid Robotics GPS Waves sensor, AirMar 200WX weather station and a Turner C3 Fluorometer (measuring turbidity, chlorophyll-a and hydrocarbons).

The Wave Glider uses a wet-bay payload system where the main hull is fully exposed to the ocean allowing easy integration of new instruments while a common power, communications and data bus provides full integration of sensors into the control unit with data being sent back at a configurable rate (every 10 minutes for this mission) via phone or satellite link. A web based portal is provided for data access, analysis and mission planning. Responsibility for mission operations and piloting was given to Liquid Robotics although it is possible to control the Wave Glider via a browser from anywhere in the world.

The Wave Glider was deployed from the R.V. Cape Ferguson (Figure 1) near AIMS on the 19th of September 2017 and was recovered not far from the Yongala NRS buoy on the 26th. Part of the mission was testing the deployment and recovery which was straight forward even in the poor weather encountered (15-20 knots and 1m seas).

The Wave Glider was tasked to undertake a series of transects through the reef matrix in the central GBR, including crossing shipping channels, collecting oceanographic data (via the CTD, ADCP, GPS Waves and Fluorometer) in a process equivalent to what an underway vessel would do. The glider was programed to undertake a course around pre-defined way-points with 2nm exclusion zones defined around reefs to ensure the glider stayed in navigable waters. It was also programmed to avoid large vessels based on their AIS signal.

Figure 2 shows the track of the Wave Glider overlaid with the chlorophyll-a data as well as ocean current speed and direction and bottom depth from the ADCP. The glider was able to stay exactly on track in hydro-dynamically complex areas around reefs, was able to remain outside of the pre-defined exclusion zones and avoided a number of vessels when crossing shipping channels using the vessel based AIS data.

The Wave Glider was also tasked with keeping station near a DSITI Datawell Wave-Rider buoy and the Yongala NRS to compare the glider data with the surface (0-10m) mooring data.

Preliminary analysis of the Wave Glider data against the Wave-Rider buoy (Figure 3) shows good agreement for the wave direction (r2=0.87) and height (r2=0.83) but less so for wave period (r2=0.31). This reflects that the mooring of the buoy will filter out certain wave periods while the floating nature of the glider filters out others. The difference can be corrected for a given wave spectrum.

Data from the sub mounted Wave Glider CTD (9m) and the Yongala NRS equivalent are shown in Figure 4. The CTD data shows good agreement between the glider and mooring based instruments although the glider was only at the Yongala NRS for a short time so more work is needed to validate the use of the Wave Glider for mooring style observations.

The results show that data collected along transects compared to what can be obtained by an underway vessel. Due to the ability to better sample surface and sub-surface waters without extensive use of pumps, de-bubblers and so on, the performance should be better than what can be obtained with a larger research vessel for the same type of instrumentation.

For surface waters (0-10m) the Wave Glider should perform better than a sub-surface ocean glider in that, unlike the ocean glider, the Wave Glider always has an accurate location and access to extensive renewable power. It is also acoustically quiet and so suitable for passive and active sonar work.

The ability to station keep allows it to collect data equivalent to a mooring although the way the Wave Glider and moorings function is fundamentally different (as seen in the wave data) and so more work is required to compare the two data streams. The Wave Glider has an advantage over a fixed mooring in that the data is real time, the glider is operationally more flexible and more cost effective but, while it can tow deeper sensors, it is limited to surface (0-10m) observations although the ADCP can profile into deeper water.

The platform performed almost flawlessly being able to maintain a precise course, dealing with shipping lanes and out of bounds areas, avoiding larger vessels and, with the ability to see the real time data, to alter the mission course as required. The use of the solar powered thruster allowed for ‘sprints’ to get to a particular point at a particular time for recovery or set sampling (such as sampling a point over a tidal cycle).

We were impressed with the level of technology readiness of the Wave Glider with sophisticated deployment, mission planning, operation and recovery systems in place and a well-developed ability to customise and extend the base platform. The Liquid Robotics Wave Glider easily met the NASA Technology Readiness Level-9 criteria as: “actual system flight proven through successful mission operations” and as such, from this evaluation, is operationally ready.

The mission demonstrated the value and capability of the Wave Glider as a cross-shelf platform. The flexibility in sensors systems, in its ability to undertake repeat and adaptive sampling missions, to capture data equivalent to existing IMOS data streams, and the level of technology readiness inherent in the product and its supporting systems, means that it represents a potential valuable platform for IMOS.

Liquid Robotics is a Boeing Company.

Categories:  news, Facility, Ships of Opportunity, National Mooring Network, Node, Q-IMOS, Home Slider

Figure 2a: Wave Glider Mission Path also showing changes in chlorophyll a concentrations.

Figure 2b: Current velocity and direction in the top 40 metres below the Wave Glider for the first five days of the mission clearly showing the effect of tides on currents. The bottom can be seen in the first and last days of the graph and the lines at 8 and 16 metres show the effects of the underwater propulsion mechanism and a shadow.

Figure 2c: Current velocity and direction in the top 40 metres below the Wave Glider for the first five days of the mission clearly showing the effect of tides on currents. The bottom can be seen in the first and last days of the graph and the lines at 8 and 16 metres show the effects of the underwater propulsion mechanism and a shadow.

Figure 3: Comparison between waves measured on a fixed Datawell Wave-Rider buoy and the Wave Glider (top: wave height, middle: wave period, bottom: wave direction) after correcting for coastal wave domain.

Figure 4: Comparison between ocean temperatures measured on the Wave Glider and the Yongala NRS