On February 19, 2014, the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite flew over the Great Lakes and captured this striking false-colored image of the heavily frozen Great Lakes — one of the hardest freeze-ups in four decades.
According to the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory (GLERL), ice cover on North America’s Great Lakes peaked at 88.42 percent on February 12 to 13 – a percentage not recorded since 1994. The ice extent has surpassed 80 percent just five times in four decades. The average maximum ice extent since 1973 is just over 50 percent.
Unusually cold temperatures in the first two months of the year, especially in January, are responsible for the high ice coverage. Very cold air blowing over the surface of the water removes heat from the water at the surface. When the surface temperature drops to freezing, a thin layer of surface ice begins to form. Once ice formation begins, persistently cold temperatures, with or without wind, is the major factor in thickening ice.
This false-color image uses a combination of shortwave infrared, near infrared and red (MODIS bands 7,2,1) to help distinguish ice from snow, water and clouds. Open, unfrozen water appears inky blue-black. Ice is pale blue, with thicker ice appearing brighter and thin, melting ice appearing a darker true-blue. Snow appears blue-green. Clouds are white to blue-green, with the colder or icy clouds appearing blue-green to blue.