Ice caps essentially are small versions of the ice sheets. Typically they're less than 500,000 square kilometers, although in reality most of them are much smaller than that -- on the order of several thousand kilometers squared. And they, like the ice sheets themselves, are the result of accumulations of snow that have been compacted over many thousands of years. And they in some cases are the remnants of a larger ice sheet such as the Laurentide Ice Sheet, which covered all of North America, and in other cases they simply have grown in the locations that they are in response to the snowfall that's occured there. In particular in the Canadian Arctic, the Arctic has seen the largest most direct impact of climate change and the ice caps themselves since they're much much smaller masses than the larger ice sheets, they respond much more quickly to temperature changes. NASA has been monitoring these for almost 16 years. We began with flights with some of our aircraft in 1995, using just a laser altimeter and Operation IceBridge is adding to that data set, extending it, along with the ICESat data that had been collected before, and so it's our hope that we by combining these data sets will have a long-term time series about what's happening there so we can better understand the dynamics of the ice caps as well as use them as early warning indicators of what is happening in our climate. I would characterise it as, this is the place where we have the most important feedback mechanism into the climate itself. The ice in the Arctic is one of the principle reflectors of energy coming from the sun and the disappearance of that ice means that not only does the temperature of the Earth change, but it also means that circulation patterns in the ocean and in the atmosphere change in response to that. So it's really critical to monitor how quickly the ice is disappearing.