November 11, 2022 - Fog and Snow in Canadian Rockies
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On November 9, 2022, the Canadian Rockies were washed in shades of
white and gray in this true-color image acquired by the Moderate
Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra
satellite.
These shades are typical on snowy days in the Rockies, when a light
coat of snow coats vegetation, heavy snow sits in high elevations, and
fog fills the valleys. In true-color images, it is sometimes easier to
use texture rather than color to sort out white-toned surfaces. For
example, fog (low cloud) is liquid water while snow is frozen ice
crystals. Fog droplets are much smaller than crystals of ice, and these
differences can be seen in the softer texture of the fog. Deep snow
tends to have a relatively smooth surface, so it reflects light back
strongly and appears bright white. Both the round droplets that make up
fog and the variable texture of light snow sitting atop grasses or
trees reflect light in varying directions, and less directly back to
the sensor, so they appear much less bright than deep snow and may even
look gray in true-color images.
Although the texture and brightness in true-color images are useful,
when scientists want to more clearly understand where snow stops and
fog begins, they turn to false-color images. The image directly below
our true-color Image of the Day is the false-color version of the same
image. The false-color image uses infrared and visible light (MODIS
bands 7,2,1) while the true-color image is created by visible light
(MODIS bands 4,3,1). While the true-color image shows shades of white
and gray, the false color image is quite bright and it is simple to
separate fog, cloud, liquid ground water, and vegetation. Fog looks
white, snow appears electric blue, while deep water (rivers, streams,
and lakes) looks deep blue. Vegetation looks bright green and open soil
would appear tan. Where light snow sits atop vegetation, the colors of
the predominant land cover may appear strongest or the area may be
tinted blue-green.
Image Facts
Satellite: Terra
Date Acquired: 11/9/2022
Resolutions: 1km (553.7 KB), 500m (1.4 MB), 250m (1.2 MB)
Bands Used: 1,4,3 and 7,2,1
Image Credit: MODIS Land Rapid Response Team, NASA GSFC
https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2022-11-11
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