From: liz@poppyrecords.invalid.invalid   
      
   Don Y  wrote:   
      
   > On 11/18/2025 2:39 AM, 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.   
   >   
   > But the cloud cover wouldn't instantaneously change from observations   
   > made during the preceding daylight/twilight periods.  I.e., "THIS is   
   > what cloud cover looks like and THAT is what clear skies look like,   
   > in the Ir" (assuming both are present)   
      
   In the UK there can be hourly changes in the cloud cover from clear to   
   90% cover as 'fronts' are blown across the country.   
      
   I think you might have to measure daylight and darkness observations   
   differently.  The apparent temperature of the clouds will increase when   
   they are in sunlight - but so will the apparent temperature of the space   
   in between them, which is filled with illuminated dust particles.   
   >   
      
   > Think about how "you" can tell the condition of the skies without   
   > even looking upward:  "It's not *bright* enough for 1PM" or "The light   
   > is the wrong 'color'"...   
      
   Recently I haven't even needed to look out the window to guess at the   
   weather.   We had a period of several days of continuous thick black   
   cloud cover when the ambient light level was so low I needed to switch   
   on lights to see around the house.   If you are only interested in the   
   oveall cloud cover, rather than mapping the clouds, an ORP12 and a 1.5v   
   battery would work in daytime.   
      
      
   --   
   ~ Liz Tuddenham ~   
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