The Canadian Coast Guard icebreaker ship Louis S. St-Laurent is mapping the seafloor near the North Pole this weekend, as Canada prepares to stake a claim to territory beyond the 200-mile nautical limit in Arctic waters.

It is the third and final year of an Arctic mapping project to collect data about the reach of the continental shelf under the Arctic Ocean, Canada's least known and least mapped ocean. It's part of a decade-long effort to improve knowledge of the sensitive area.

According to Mary-Lynn Dickson, chief scientist on the expedition, Canada could add about two million square kilometres to its territory, about the size of three additional Prairie provinces, if its application for jurisdiction over the continental shelf under the Arctic Ocean is successful.

Mapping the Arctic seabed is a difficult and expensive operation, said Denis Hains, director general of the Canadian Hydrographic Service, part of Fisheries and Oceans Canada,

There's a very short window when Canadian ships can access the area and even then ice may complicate efforts to map the areas where scientific data is needed.

That means lost time and lost opportunity to gather data, Hains told CBC News.

Close to the North Pole

In 2014, the St-Laurent and fellow icebreaker CCGS Terry Fox had their voyages slowed by thick ice. But in 2015 and 2016, ice conditions are better and Canada has been able to successfully gather data next to the pole.

The St-Laurent is travelling with a bigger ship, Swedish icebreaker Oden, which has cleared a wider swath where hydrographers can work.

During a seven-week voyage together, the Oden will also be measuring geophysical waves refracted from the subsoil below the seafloor.

On Thursday, the two ships were 224 nautical miles east of the magnetic North Pole, about 90 kilometres south of the geographic pole, according to Hains

​Discovery of underwater volcanoes

Already, on its way north to the Arctic, hydrographers aboard the St-Laurent made a significant discovery — a chain of 25 to 30 undersea volcanoes south of Greenland that are uncharted.

A multi-beam image shows underwater volcanos discovered on the seafloor south of Greenland. (Fisheries and Oceans Canada/Canadian Coast Guard)

Some volcanoes nearby were discovered last year, but this year's pass over the area revealed an extensive string of them.

"The technology we use is covering a corridor, we just sailed parallel to this corridor to overlap the corridor of last year," Hains said.

"You have a limited path under a ship, but you see the entire image, so that's where we can detect in three dimensions volcanoes and mountains," he added.

The Canadian Hydrographic Service uses multi-beam echo sounder technology to measure the depth of the ocean and create a detailed image of the topography of the seafloor.

A multi-beam sensor device is mounted in the hull of the survey vessel to send out a sweep of high or low frequency signals or "pings" and to pick up the echoes from the seabed and calculate the depth. Many factors have to be taken into account in the measurements, including the variable sound velocity in the water column and the tide,.

At the same time, Natural Resources Canada is doing a seismic survey, sending sound waves through the ocean to measure the thickness of sediment on the bottom. It also takes core samples and tests the rock and subsoil to better understand the geology under the Arctic Ocean.

Paola Travaglini, right, is lead hydrographer aboard the St-Laurent. She is shown at work with Canadian Hydrographic Service hydrographer Darren Hiltz. (Fisheries and Oceans Canada/Canadian Coast Guard)

This year's mission will map parts of:

Lomonosov Ridge.

Amundsen Basin.

Marvin Spur.

Makarov Basin.

Under Article 76 of the United Nations Convention on the Law of the Sea, nations can lay claim to the continental shelf which is an extension of their land mass in defining the 200-mile limit over which they have control of resources. But they have to be able to prove the claim.

Making a case for Canada

What is defined as "continental shelf" depends on a combination of the thickness of the sediment and the depth of the water.

"What we're trying to find is the foot of the slope of the continental shelf — it's simple to say, but it's not that simple to have scientific evidence that provides that," Hains said.

Global Affairs Canada, a partner with Fisheries and Oceans and Natural Resources Canada in the mapping project, will be putting an application into the UN in 2018, after all the findings have been analyzed.

"There's a lot of data that we are capturing. We have to analyze, validate and correct it — because of ice there is some 'noise' in the data, so we have to do additional processing," Hains said.

Canada won't be the only claimant wanting to extend control over Arctic waters — Denmark, Russia, Norway the U.S. are also staking claims.

It's good for Canada to map its continental shelf and claim more of the Arctic Ocean, because of the potential economic benefits and the need for environmental protection for the region. But another critical function of the voyage is to update navigation maps, he said.

Need better navigation charts

"With the increase of commercial shipping in the Arctic most are travelling in more risky areas. We will need better charts." Hains said.

The planned voyage of the Crystal Serenity through the Northwest Passage this summer, which already raised concerns about ship traffic in the Arctic, may presage more large cruise ships.

Most ships now use established routes that have been shown not to have shoals, but the Canadian Hydrographic Service plans to map more intensively in corridors parallel to these shipping routes to try to improve navigation maps.

Canada has a five-year partnership with the Swedish polar research secretariat, which could mean more polar expeditions for Natural Resources Canada. The Canadian Hydrographic Service plans to piggyback on such research expeditions, as well as commercial voyages, to enlarge its knowledge of the Arctic Ocean, Hains said.