Posted on 26 June 2017

Uncovering the seas’ secrets

Meet Betty, an amazing piece of marine technology that gives us detailed information about the oceans that we couldn’t get any other way.

The oceans remain one of the world’s biggest mysteries. Although seas cover 71% of earth, we know less about them than we do the moon.

One aspect that has been difficult to investigate is ocean stratification – layers of temperature and salinity below the water’s surface. This is now possible thanks to the latest marine technology: ocean gliders. Gliders have been around for just 10 years but have already made a huge difference to oceanography.

“Betty provides us with the unseen,” said Dr Joe O’Callaghan, a Coastal Physicist who leads NIWA’s ocean glider facility. “Gliders are mapping the ‘weather’ of the ocean, equivalent to watching clouds move through the sky. The ocean isn’t uniform, patches of water have different salinity, temperature, oxygen and other environmental conditions, which move and shift over time.”

Environmental conditions in oceans can’t be measured in any other way that would give the richness and complexity of glider data. Boat-based methods can only cover a limited area for a limited time. Satellites can cover large areas, but can’t penetrate below the surface.

There are less than 1,000 ocean gliders in the world. Betty is one of just two gliders in New Zealand. She and her sister Manaia both call NIWA home.

Mini yellow submarines

Ocean gliders are 1.5m long and look like mini submarines. They travel through the water at about 0.5 knots, see-sawing from the surface down to a depth of 200m. They continuously take measurements of:

  • Temperature
  • Salinity
  • Light
  • Oxygen
  • Chlorophyll
  • Turbidity

Betty also has an acoustic sensor that listens for marine mammals during glider missions. Matching sounds to location and environmental conditions is another way to learn about the places marine mammals live and feed.

Gliders surface every 2–4 hours to transmit data and their GPS location. This is as near to real-time data as it’s possible to get.

“I generally set Betty to surface every 2 hours so I can see where she is and check that she hasn’t been swept too far off course by currents,” says Joe.

Efficient engineering

Despite not having a propeller, ocean gliders can steer and stick to a course thanks to fixed wings, a buoyancy engine and a rudder.

  • The fixed wings convert downward fall into horizontal motion – meaning they glide through water rather than sinking.
  • The buoyancy engine uses just 230ml (about a cup) to control the glider’s decent and ascent.
  • The rudder means you can steer the glider – as long as the currents aren’t more than 0.5 knots. If the glider gets swept off course by a strong current you can send it new instructions when it surfaces.]

The buoyancy and rudder are both battery-powered.

There is also a battery-powered air bladder at the tail, where the transmitter is. When the glider surfaces this bladder inflates, lifting the tail higher and making transmission more efficient.

In a final touch of efficient design, batteries at the front of the glider are on a track so their weight can shift, helping the glider ascend and descend.

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