Visible and Infrared (IR) Weather Satellite Interpretation
1. Visible satellite images are coded from black to white according to the amount of reflected
sunlight. Clouds, snow, and ice appear white because they reflect 40 to 90% of the sunlight.
Thicker clouds reflect a higher percentage of light and appear brightest, but different clouds are
identified mainly by their appearance. Cumulus appear as dots, cumulonimbus appear as pop
corn, cirrus appear fibrous, and layer clouds associated with storms cover much larger areas
and appear as large commas or spirals. Fog and low stratus are generally not so bright and are
very smooth. They are most prominent in the morning and over cold ocean waters. Dry sand
reflects 30 to 40% of the sunlight and appears gray. Bare earth – soil and rock – and vegetation
appear dark because they reflect only 7 to 15% of the sunlight. Surprisingly, water appears
darkest because except for direct sun glint it reflects 5% of the sunlight.
2. Infrared (IR) satellite images record heat radiated from the surface and from clouds. They are
temperature maps artificially colored either by a spectrum in which red represents high
temperature and blue or purple represents low temperature, or in gray tone where black
represents high temperature and white represents low temperature. Because temperature
generally decreases with height in the atmosphere, opaque clouds with tops high above sea
level, such as cumulonimbus are extremely cold and appear blue (or white) while clouds whose
tops are near the ground such as fog and low stratus or stratocumulus are so low they can
barely be distinguished from the ground. Cirrus also appear blue (or white) provided they are
thick and opaque. Small, spotty clouds such as cumulus appear warmer than they are because
the radiation is an average of cloud and ground temperature. Land is usually hotter than water
on sunny afternoons but colder than water late at night or very early in the morning.
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Interpret the features in the next 3 slides.
1. The cloud form is ________. The reasoning is ___________________________________
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2. The cloud form is ________. The reasoning is ___________________________________
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3. The cloud form is ________. The reasoning is ___________________________________
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4. The time of day is ________. The reasoning is ___________________________________
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5. The cloud form is ________. The reasoning is ___________________________________
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6. The cloud form is ________. The reasoning is ___________________________________
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