From: '''newspam'''@nonad.co.uk   
      
   On 28/11/2025 23:35, Don Y wrote:   
   >>> Do I need that much more "resolution" than simply imaging (sky and   
   >>> soil) with an Ir camera?   
   >>   
   >> The idea is to have a two pixel imaging system consisting of a pair of   
   >> thermometers with low thermal inertia one facing upwards shielded from   
   >> the ground and another that is ground facing and shielded from the sky.   
   >   
   > The thinking being that "change" is quick and sudden?   
      
   It is essentially a fairly pure measurement of radiative heat loss to   
   the sky which will under most circumstances be a very good guide.   
      
   Once you have a few temperature curves for typical conditions that's   
   good enough. High cirrus can make quite a difference to thermal losses   
   to the sky although nothing like as much thick low cloud does.   
   >   
   >> The temperature difference and its rate of change gives you the extent   
   >> to which the situation is likely to allow a frost and/of fog to form.   
   >>   
   >> You also need windspeed and relative humidity. This is probably the   
   >> simplest kit configuration to predict risk of frost of fog.   
   >>   
   >> Dew point was always very important to astronomers and highway traffic   
   >> monitors so you can get purpose built kit for this sort of thing.   
   >   
   > We used to used chilled mirror sensors for dewpoint.  But, were   
   > concerned about   
   > *actual* dewpoints as we were regulating a thermodynamic process.   
      
   We were mainly concerned with not getting condensation onto the optics   
   or mast head amplifier depending on the type of receiver/sensor.   
      
   > I think I can cut corners, here, as I am looking for "correlations" and not   
   > "numerics":   
   >   
   > "When I see this set of conditions, the following has proven to be true..."   
      
   I think what we have proposed might be OK for that and fairly robust   
   minimal & cheap too.   
      
   --   
   Martin Brown   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)