From: jrr@flippers.com   
      
   On 2025-11-18 1:39 a.m., Liz Tuddenham wrote:   
   > Don Y  wrote:   
   >   
   >> Particularly, cloud cover.   
   >>   
   >> How can I quantify the extent and "density" (opacity) of cloud   
   >> cover?   
   >>   
   >> And, to make it even more interesting, doing so AT NIGHT, as well?   
   >   
   >   
   > At night the clouds would appear warmer than space, so an infra-red   
   > scanning system would give you a picture of the clouds.  I don't know   
   > how you would calibrate it, because the apparent cloud temperature would   
   > depend on air temperature and IR radiation from the earth.   
   >   
      
   I wonder it it would also show the water vapour tracks left by jets?   
      
   John :-#)#   
      
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