Contrails - Research, comments and links

Contrails and Aviation-induced Cirrus Clouds

Effects on quality and quantity of Sunlight (01)

So, what does all this have to do with satellite images?  You see a cloud because its constituents (water droplets) scatter and reflect sunlight.  So does the satellite.  Clouds appear white because the water droplets scatter all of the wavelengths in the visible part of the spectrum. 
   The waves and arrows represent sunlight hitting the cloud and being scattered to a satellite looking down from above.  Thicker clouds have more drops to reflect the light and thus appear brighter.  What the satellite sees is the top of the cloud.  Any sunlight that penetrates the cloud may also be reflected, but the reflected light will be scattered again, so it won't get back to the satellite.
    What about the rest of the spectrum?  Any UV that is scattered off the cloud tops would just make the image fuzzy, so the satellite optics filter the UV out.  However, optics that sense infrared can "see" into the cloud.  
    The IR waves are so long that most of them miss the water droplets.  That's what happens to the IR component of sunlight -- most of it just passes through the cloud.  However, the droplets themselves are emitting IR radiation (just like the hot stove, except that the waves are less energetic and much longer).  These waves also pass through the cloud, and the ones going upward are what the satellite sees.


Contrails are Bad News