Think all ice formations are basically the same? Think again. This Radarsat-2 satellite image, captured on Jan. 1, 2012, reveals ice cover in Viscount Melville Sound, in the Northwest Passage, at a resolution of 100 metres per pixel. It shows how many types of ice can be found in one area and what mariners are up against when traversing the Arctic.
The Canadian Ice Service analyzes images like this for Canadian regions of the Arctic Ocean where there is shipping traffic. Radar images are used to map ice topography; other types of satellite images can reveal the thickness of the ice or more clearly demarcate the boundary between ice and open water.
In winter, when shipping traffic is low and much of the ice is stationary, images are updated weekly. In summer, they are updated daily. Meteorologists also use such information year-round to monitor trends in ice cover.
1 Multi-year ice, shown here, is rougher than first-year ice, having experienced years of melting and refreezing, collisions with other ice floes and crushing within the mobile ice pack. In radar images, rough surfaces look bright and smooth surfaces look very dark.
2 Medium first-year ice ranges from 70 to 120 centimetres thick. Radarsat images are cross-referenced with other satellite images to derive ice thickness.
3 Resolute Bay, strategically located on Parry Channel, in the Northwest Passage, will see infrastructure expansion due to increased commercial and military activity in the Arctic.
4 Multi-year ice floes can sometimes be confused with small islands. A red outline distinguishes land from sea and ice.
5 Thin ice generally has a smoother surface than multi-year ice. In windy conditions, when thin ice is on the move, its surface can appear rough in a satellite image. To distinguish thin ice from multi-year ice, infrared satellite images are used to complement radar, because they indicate ice temperature and thickness.
6 Landfast ice forms in calm waters, particularly in sheltered bays, and tends to be smooth; it therefore appears dark in radar images. In summer, however, rough surfaces can also appear dark when meltwater accumulates. During these times, care must be taken not to mistake rough, multi-year ice floes with smooth, thin ice surfaces.