Icebergs and satellite imaging
Spindrift for Schools

By  Dona Bertarelli

I want to thank all our partner schools, in France and Switzerland, and the 2,000 students who are following us. Whenever I can, I will be answering your many questions throughout this journey around the planet, a journey that we are taking together to discover the wonders of our world.
With all the crew of Spindrift 2, through our observations and our encounters, not only with marine life, but also with the islands and peninsulas that we pass, with the meteorological phenomena we experience, and with the birds and the stars that accompany us during our voyage, we will help you to live this adventure, like Phileas Fogg in Jules Verne’s famous book. We are calling our Spindrift for Schools series - Out of the Classroom.

Questions from Petit-Paris school in Brest (France)

When we decided to attempt the Jules Verne Trophy, we knew our journey would take us a long way south, into the Furious Fifties, where icebergs and growlers can be found drifting.

An iceberg is a chunk of ice that has become detached. There are many reasons why this might happen, but scientists agree that global warming and the melting of the ice caps are the main cause. NASA and the University of California explain in a study they published in Science in May 2014 that the western Antarctic is melting fast and its decline is irreversible.

Icebergs are 90% fresh water. The upper layers may be snow that never melts, but the heart of an iceberg is made of very hard, grinding ice that can be up to 150,000 years old. Only a third of the surface of an iceberg is visible, with the rest submerged under water. When an iceberg breaks free, many fragments, known as “growlers”, break away too, sometimes weighing several tonnes.

In February 2010, the National Ice Center, which tracks icebergs in Antarctica, detected 37 giant icebergs. The largest ever recorded broke away from the Ross Ice Shelf in 2000, with an initial surface area of 11,000 km².

Icebergs can drift for years before they melt. They can rotate around Antarctica several times, each time at a greater distance from the continent. That explains why we saw a 2km² iceberg at 47ºS in the Indian Ocean. There were other, smaller icebergs (100m²-400m²) at 51ºS.

“And now there came both mist and snow,
And it grew wondrous cold:
And ice, mast-high, came floating by,
As green as emerald.
 
And through the drifts the snowy clifts
Did send a dismal sheen:
Nor shapes of men nor beasts we ken—
The ice was all between.
 
The ice was here, the ice was there,
The ice was all around:
It cracked and growled, and roared and howled,
Like noises in a swound!”

Extract from The Rime of the Ancient Mariner , by Samuel Taylor Coleridge

Several months before we started our circumnavigation, we hired the services of CLS (Collect Localisation Satellites), one of the world’s leading iceberg-detection companies.

I asked Vincent Kerbaol, radar applications director and head of the CLS site in Brest, to explain their work.

To understand our work, I should first explain that CLS specialises in operations on satellite systems, with more than 80 instruments on around 40 satellites, and providing services for those systems.

Those who are old enough will remember CLS for ARGOS, a system that made the company famous in the 1980s, monitoring sailors and fleets during sailing races. The ARGOS system is widely used today for science and for monitoring land and sea animals.

CLS is also, for instance, a long-standing operator of altimeters (TOPEX, POSEIDON, JASON, etc.), which have measured average sea levels across the globe for more than 20 years. These are the measurements that allow the scientists at the IPCC [Intergovernmental Panel on Climate Change] to say that the sea levels rise at a rate of 3.3 mm a year.

Today, CLS operates three types of satellites on a daily basis: mobile tracking satellites for things that move, such as animals, boats and buoys; Earth-observation satellites for measuring sea levels, swell, wind, temperature, currents, etc.; and high-resolution satellite imaging to detect pollution, ships, and icebergs!

High-resolution satellite radar imaging is used to monitor ice. Radar technology allows us to observe the sea surface during the day and at night, regardless of the amount of cloud cover. We obtain the largest satellite radar images that exist, covering 500 km by 500 km. Their 100 m spatial resolution means we can detect icebergs as small as 100 m long. Of course, when we detect these ‘small’ icebergs, smaller icebergs can be expected near by.

Although 500 km x 500 km sounds enormous, it is merely a postage stamp compared to the vast oceans of the south, so we also use other sources of information to refine our knowledge of the presence of icebergs:

- Altimeters measure average sea levels, and can detect icebergs when they travel through the beam. They are used in all the oceans, but unfortunately are not as precise as radar imagery.

- Satellite data, meanwhile, measure water temperature from space, another excellent indicator of the presence of ice.

- When there is a specific risk in an area, we programme the radar satellite imagers to scan the surface for icebergs.”

Since the Cape of Good Hope, CLS has alerted us to 34 icebergs of different sizes. These data have enabled us to adjust our course not always to improve performance, but to improve our safety.