EUMeTrain: Water Vapour CAL Module - Water Vapour Channels

What does the satellite measure in water vapour band?

Basic radiation processes can be seen in the image below.

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The radiation from the sun goes into the Earth and warms cools warms it. The Earth emits heat radiation in the visible infrared infrared wave lengths. Water vapour in the troposphere absorbs this radiation and re-radiates it into the atmosphere in a longer shorter longer wave length.

The ability of the radiation in water vapour band to pass through atmosphere depends on the density of the water vapour, thus showing the amount of liquid water humidity humidity in the atmosphere.

The Range between 5.2 µm and 8.5 µm are referred to as water vapour channels. In Meteosat MSG satellites there are two water vapour channels, 6.2 and 7.3 µm.