December 25, 2021 - Snow in the Alps

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Snow in the Alps
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Each year on December 25, many Americans cloak their homes and hearths
in reds and greens as they celebrate the popular holiday of Christmas.
These colors have become intertwined with the seasonal celebrations for
as many years as anyone living can recall, although the exact reason
they mark the Christian holy day isn’t exactly clear. Some give the
colors religious symbolism, with red representing the blood of Christ
and green reminding of the “eternal life” of the evergreen trees that
stand resplendent in the harshest winter. Others believe that the
colors come from the green leaves and bright red berry of the holly
tree—a stunning plant at its most showy during mid-December. Kids might
say it’s from the bright red nose of Rudolph, the reindeer who is said
to pull Santa’s sleigh on Christmas Eve, and the deep green of the
traditional Christmas tree.

For scientists looking at false-color satellite imagery, however, reds
and greens have nothing to do with Christmas, and everything to do with
the reflectance of various features on Earth.

On December 19, 2021, the Moderate Resolution Imaging Spectroradiometer
(MODIS) on board NASA’s Terra satellite acquired a stunning false-color
image of snow across the Alps. By using blue and shortwave infrared
light (MODIS bands 3,6,7) to highlight the different reflectivity of
snow, ice, clouds, and vegetation, the image lights up in green and
red. The bold green marks area of vegetation while bright red marks
highly reflective and cold snow or ice. Liquid water would appear deep
red or black, while clouds appear white or, if they contain ice
crystals, may look peach.

Heavy snow lies across the high elevations of the Alps. The Apennines,
which run down the length of Italy, also carry some snow as do the
mountains on the island of Corsica. A large bank of cloud over the
Adriatic Sea extends a long finger to cover most of Italy’s Po Valley.

Image Facts
Satellite: Terra
Date Acquired: 12/19/2021
Resolutions: 1km (1.8 MB), 500m (5 MB), 250m (3.5 MB)
Bands Used: 3,6,7
Image Credit: MODIS Land Rapid Response Team, NASA GSFC



https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2021-12-25

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