Niwa's yellow submarine, the Slocum Glider, unveiled

Joanne O'Callaghan stands behind one shiny new Slocum Glider. Photo / NIWA / Dave Allen

High-tech ocean explorer roams independently to gather data on changing world.

A state-of-the-art underwater glider - the first of its kind in New Zealand - is set to uncover new insights into our offshore environment.

The torpedo-like Slocum Glider, one of about 500 in the world, was unveiled in Wellington yesterday at the National Institute of Water and Atmospheric Research (Niwa).

With an array of sensors that can measure temperature, salinity, light, oxygen and fluorescence below the surface of the ocean, the 1.5m glider is an impressive tool for learning more about New Zealand's Continental Shelf, where water is shallower than a few hundred metres.

Niwa coastal oceanographer Dr Joanne O'Callaghan said the glider's instruments could crucially tell us how our oceans are changing - particularly as a result of human impacts on land - while also improving the models we already have.

"There've been satellites collecting measurements about the ocean's surface for more than 30 years, but just as the weather constantly changes above us, so does the ocean below."

The bright yellow gadget will first be deployed off the northeast of New Zealand during the autumn, transmitting data via a phone call made during occasional surfacing.

As the glider was designed to travel the oceans alone, scientists only had to programme co-ordinates it would travel between, over deployment periods that could stretch to a month or to distances of 400km.

"The real-time series it would provide will be incredibly useful, while we'll also be able to use it in severe sea conditions when sampling from a vessel wouldn't be possible," Dr O'Callaghan said.

Unlike powered submarines, it did not use a propeller to move through the water and instead travelled by changing its buoyancy to glide up or down in the ocean.

The glider had a saw-tooth dive pattern to depths of 200m, and a slow horizontal speed of about 1km/h.

But Dr O'Callaghan said this was far more effective than the previous data-gathering method - manually collecting samples from the decks of research vessels.

Underwater volcano yields secrets

Another underwater robot has given scientists a clearer understanding of a huge submarine volcano near the Kermadec Islands.

As part of a multi-year programme by GNS Science, New Zealand and United States researchers have just returned from the Macauley Caldera - a large crater-like structure roughly the size of Wellington Harbour and about 100km south of Raoul Island.

The team on board the navy patrol vessel HMNZS Wellington used an underwater vehicle called Sentry to map the caldera at a resolution of 0.5m.

The evidence they found supported a hypothesis that the caldera had erupted many cubic kilometres of material around 6300 years ago.