Surf's up! Wave glider trials in the North Sea
05 February 2013
Scientists at Cefas are trialling a clever device that looks
like a surf board but packs a wide range of sophisticated
instruments to record a variety of marine conditions.
The autonomous wave glider, hired from US firm Liquid Robotics, was deployed off
Lowestoft on 30 January. This marks the first time such a device
has been tested in the southern North Sea, where tides and currents
are strong and shipping is busy.
The 2m-long wave glider is self-propelled
by wave action and has the capacity to travel thousands of
miles. It is steered remotely from the operations base and has a
built-in automatic identification system, which means that it can
send alerts with advice to actively avoid shipping.
The suite of systems onboard the device is powered by batteries
recharged by solar panels.
Alongside the standard fitments - of weather station, wave
height and temperature sensors - the Cefas scientists have added
instruments to measure oxygen concentration and saturation,
turbidity (water cloudiness), the chlorophyll fluorescence of
phytoplankton and salinity. These observations are being recorded
by a specially integrated Cefas data logger and data are
transmitted to shore via satellite telecommunications in near
"real-time".
During the Cefas trial, which runs to March, the glider will
transit north to Cefas' own
Dowsing SmartBuoy site, about 25 miles off the Norfolk and
Lincolnshire coasts. There it will make a comparison of the sensors
on the wave glider with those on the SmartBuoy. After a few days of
monitoring activity, the glider will set off for another SmartBuoy
site further south at
West Gabbard, 30 miles from the Suffolk and Essex coasts. It
will then repeat the same monitoring pattern as at the Dowsing
site.
The wave glider travels at around 1.5 knots and will need to
cope with strong tides so the 120-mile journey between the two
SmartBuoy sites may take several days. Once its work at the Dowsing
site is completed, it will turn north and transit back to Lowestoft
for recovery (see map).
Wave
glider's North Sea route: green line indicates initial
transit to first, northern SmartBuoy site; the stars mark SmartBuoy
locations; black line shows the trial route
Jo Foden, Cefas' Project Manager for these trials, said: "At
present our observations at sea are made from a variety of
platforms: moored instruments such as the SmartBuoys, plus our
research vessel, FerryBox systems on ferries and other ships,
satellite, etc. Despite this range, there are still some important
gaps in data and our knowledge.
"The instruments mounted on the wave glider will enable us to
plug some of those gaps. For instance, they should supply greater
spatial coverage between platforms and more accurately determine
the spatial representation of our SmartBuoys' data. We also
anticipate that the instruments onboard will provide some valuable
new information: for example, the chlorophyll fluorescence data can
help to verify satellite observations, and other data will help to
calibrate and validate our marine models. So, the wave glider is a
flexible platform and new sensors can be added.
"Another big advantage of the wave glider," Jo continued, "is
the ease of launching and recovery from a small vessel. This will
mean that some costs are reduced and it provides flexibility: we
can deploy it at short notice or change its track to make
observations of unexpected and interesting phenomena at sea."
If the Cefas trial is successful there will be long-term
benefits in using wave gliders. Not only will there be validation
of a range of environmental characteristics, but there opens up the
possibility of more collaborative work with neighbouring European
states. Shared marine boundaries with neighbouring states have been
areas of contention in the past, so a glider could be programmed to
sample transboundary waters across the North Sea for bilateral
research studies. This could save money and provide improved
scientific understanding of the marine environment.
Fact file
- The OSPAR Strategy[1] and the EU's Marine
Strategy Framework Directive (MSFD)[2] are the
key drivers of the UK's monitoring and assessment commitments.
These policies require multiple environmental characteristics to be
measured in near- and off-shore waters.
- Nutrient, chlorophyll and phytoplankton data are vital for
calculating the MSFD's indicators of Good Environmental Status, and
to establish the thresholds for the assessment of eutrophication -
where too much nutrient enrichment caused by human activity can
lead to undesirable disturbance to ecosystem health and water
quality.
- Some of the UK's marine areas are not well covered in annual
vessel surveys. For instance, while there is a SmartBuoy in the
Celtic Sea, research vessel time is still required to service it
and this is not sufficiently frequent to prevent data being lost
due to bio-fouling on the instruments. The data transmitted back
from a wave glider could be automatically checked for signs of
bio-fouling and then re-called or instructed to "hold station" for
cleaning if a research vessel was nearby.
- At present there is a paucity of acoustic data routinely
collected at sea. Such data are needed for MSFD assessments of
underwater noise. SmartBuoys are noisy because of their moorings,
and seabed units are vulnerable to trawling or interference. Wave
gliders, originally designed for cetacean (e.g. dolphins)
monitoring, are inherently quiet. Cefas has plans to mount acoustic
instruments onboard the wave glider in future.
[1] Strategy of the OSPAR Commission for
the Protection of the Marine Environment of the North-East Atlantic
2010-2020, OSPAR Agreement 2010-03
[2] Directive 2008/56/EC
Wave glider image © Liquid
Robotics