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Water vapour
• This is found from 6.7μm channel
• This is in the IR region of the spectrum
• This wavelength radiation is absorbed by water vapour
Atmospheric radiation
• The atmosphere is an object and has a temperature
• It will radiate IR and, in particular, at 6.7μm
• The more water vapour there is, the higher in the atmosphere the radiation has to start to avoid being absorbed and reaching the satellite
So we see
• Radiation from a certain level in the atmosphere
• This will have a certain temperature that we can find
• Finding the radiative temperature at 6.7μm tells us the height the radiation started from and therefore how much water vapour there is.
Generally
• There is enough water vapour that the radiation comes from somewhere between 300mb and 600mb
Water vapour and the jet-stream
Polar front is marked by sharp decline in atmospheric moisture toward the pole. This marks the position of the jet stream