NASA just released this image of the very frozen Great Lakes taken by one of its satellites on Feb. 19. A NOAA analysis found that the lakes were more than 88 percent covered in ice in mid-February, one of the largest freezes in four decades.
The space agency’s Moderate Resolution Imaging Spectroradiometer, carried aboard the Aqua satellite, took the false-colored image that highlights the freeze up. Analysts combined shortwave infrared, near infrared and red bands reflected from Earth to the instrument to create this picture, which highlights the difference between ice, snow, water and clouds.
A NASA release says 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. See the full-sized image here.