Do satellites sometimes see ice where there isn’t any?

Readers often ask us, “Why does your sea ice map show sea ice where there is none?” Sometimes our Daily Sea Ice Extent images show sea ice in a particular area, but when readers who live in those areas look out their windows, they see open water—or they even may see ice where our maps show open water. This occurs most frequently along rivers or near coasts. Why does this happen?

Ups and downs of passive microwave

Photograph of Qaanaaq, a small town on the Greenland coast

The rugged coast near Qaanaaq, Greenland, illustrates the challenge to satellite sensors, which must distinguish between land and ocean signals within the same image. Credit: Andy Mahoney

These discrepancies are most often caused by the resolution of the satellite sensor. NSIDC relies on passive microwave sensors to compile daily sea ice maps. These sensors have the advantage of being able to see through the Arctic’s cloudy weather and capture surface data even during long, dark winters, making them ideal for tracking sea ice. The disadvantage, however, is that passive microwave sensors often have low spatial resolution. The sensors collect data in “footprints” that are up to 50 to 70 kilometers (31 to 44 miles) in diameter. Continue reading

What does seeping methane mean for the thawing Arctic?

Photograph of bubbling methane melting a hole through lake ice

Bubbling methane melted a hole in the ice of this otherwise frozen lake in the Brooks Range, Alaska, in April 2011. Credit: Katey Walter Anthony

As people watch the decline of Arctic sea ice, the most obvious sign of climate warming in that region, scientists are noting other signs of change, like methane seeping out of the ground as permafrost thaws and glaciers melt across the Arctic. Scientists suspected these methane seeps existed, but no one had measured how much methane was escaping—until recently. Continue reading