What’s the difference between a tugboat and an iceberg? When you’re looking at a satellite radar picture taken from beyond the Earth’s atmosphere, not much. But these simple-looking black and white radar pictures from the Canadian Space Agency’s RADARSAT-1 (see below) satellite have revolutionised the way icebergs are tracked on the East Coast.
Specifically launched for Arctic observation in 1995, RADARSAT-1 has proved useful to track down icebergs and keep coastal waters free from collisions. Because RADARSAT-1 is equipped with synthetic aperture radar (SAR), it is particularly suited to the job. Radar works by reading the echoes of pulses bounced off the surfaces it is reading, in this case, the ocean’s surface.
"Radar has the capability to see through clouds, as opposed to optical imagery," says Laurent Giugni, spokesperson for the Canadian Space Agency’s earth observation department. "Even if it is raining, or night or day, it can get imagery."
Because of this ability, RADARSAT-1 compliments the iceberg tracking system well on Canada’s East Coast. The Canadian Ice Service (CIS), a division of Environment Canada, puts out daily ice reports, free to the general public, but of vital interest to fishing and transportation vessels and marine oil and gas projects. CIS uses aerial observation, ship-to-shore reports and readings on currents and water temperature from buoys to plot the paths of icebergs. As the weather does not always permit flights for aerial observation, and mapping large areas by plane can be costly, the satellite radar is a key tool.
CIS acquires some of its radar image analysis from C-Core, a research and development firm in St. John’s, Newfoundland. C-Core analyses RADARSAT-1 images mostly from the Grand Banks, off the coast of Newfoundland and Labrador, in the corridor called Iceberg Alley.
Desmond Power of C-Core describes the hunt for icebergs on a radar image as "looking for bright targets on a noisy background."
"Ships and icebergs both manifest themselves as bright targets," says Power. "We have to be able to tell the difference."
For this problem, C-Core uses algorithms to calculate the scattering of radar off each target. The wooden or metal hull of a ship gives a different reading than ice. Their software also looks at the shape and brightness of a given target to help discern icebergs from ships or other objects.
RADARSAT-1 can actually be set to pick up objects as close as eight metres on the ocean’s surface, but this sacrifices the ability to see a large area at a time.
"You are essentially taking a pencil-width slice of the ocean," says Luke Desjardins, manager of the operational section of CIS. "It would cost an awful lot of money to map the whole of Canadian waters."
Desjardins says the resolution is usually set at a compromise of 50 metres, twice as fine as the resolution CIS uses to monitor the vast sheets of sea ice. At this resolution, it’s hard to see the smallest icebergs, known as growlers for the low-level groan they make when moving on the ocean surface, or their slightly larger cousins, bergie bits. Desjardins says it’s these pesky ice pieces that often cause the most trouble.
"They tend to bob up and down with the seas and the swells and get masked by the higher seas. Any marine radar would have trouble detecting them," says Desjardins. "If your ship radar is bouncing off a huge berg, then you can see it at a distance."
But despite some of these limitations, RADARSAT-1 has performed far beyond its anticipated ability. The aging satellite is now five years past its life expectancy and working by an engineering miracle on backup systems and re-routed software.
In the event that RADARSAT-1 stops working, both CIS and C-Core order images from the European Space Agency’s ENVISAT satellite, launched in 2002. It is equipped with dual polarization which works like a pair of polarized sunglasses, helping cut down glare from the ocean surface.
Nevertheless, Power says iceberg monitoring cannot be left completely to satellites. The aerial reconnaissance done by Provincial Airlines out of Newfoundland, and the International Ice Patrol of the U.S. Coast Guard, plays a vital role.
"Satellites are not there to replace aircraft," he says. "They are a complimentary tool."
The Canadian Space Agency is expected to launch RADARSAT-2, the next generation of Canadian radar satellite in December 2006. The new satellite features three polarization modes and finer resolution than the first RADARSAT. It is anticipated to be a great improvement in the field of iceberg mapping.