May 27, 2008

Understanding the rate at which the sun’s energy is transferred from the atmosphere – through the sea ice – to the ocean in a particular summer is important to understanding the reduction of sea ice during summer we’ve seen over the last 30 years (see figure from last blog entry) and for making projections of the fate of the sea ice and its effect on global climate into the future using models. It will also help us understand why, in the summer of 2007, we witnessed the lowest extent of sea ice observed during its summer minimum since we’ve been able to measure it with satellites.

Determining how much of the sun’s energy is transmitted through sea ice into the ocean for storage would be a fairly simple task if we could do this in one place and call it a day, so-to-speak. But summer sea ice varies considerably in its complex combination of surface types on a scale of less than one square-kilometre. Deep snow, bare ice, melt ponds, open water areas, cracks, and ridges all have different physical properties that process the sun’s energy differently. We also need to identify where these different features are, and how much of each lie in a given area (i.e., their fractional coverages), if we want to if we want to determine an ‘energy budget’ for a given time and place. We’d use optical satellites to give us a picture of the surface, but a picture devoid of fog or cloud cover is a rarity in the Arctic during summer.

This is where the work of Chris and I comes in. It is known that radar satellites can be used to imageRadar equipment: Ground-based radar we use to measure sea ice. the sea ice surface regardless of cloud cover. In the Arctic we can get images almost every day of ice conditions. But during summer, when sea ice is melting, the radar signal is quite confusing and doesn’t give us a clear picture of what’s on the surface. Radar technology is progressing rapidly, however, giving us potential for new ways to decompose an otherwise confusing radar signal. We’re here with a ground-based radar that gives us a complex ‘view’ of how radar signals interact with different sea ice features (see picture). Eventually, we’ll be able to extend our understanding to complex radar images – in particular from the recently launched RADARSAT-2 – so that we can accurately identify surface sea ice features during summer. Then perhaps we can determine an energy budget characteristic of specific places!

Such is our research challenge – though the real challenge was keeping this blog entry short …

- Randy