How to monitor the foliage Evapotranspiration with arduino
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 Good day all, I actually monitor the amount of water of some appale tree in a orchard with 3 Watermark sensors. 
 In order to have better result on how and when to watering the apple orchard, I would like to monitor the evapotranspiration of the crop or better, the foliage.I once saw an evapotranspiration sensor but I can not find anymore. Someone would have a recommandation to monitor the evapotranspiration of the plants, with Arduino? (sensor, how to?...) Is there sensore for that purpose? Many thank for any tips and hints to start my task 
 
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 Wikipedia has some clues. A scintillometer which measures fluctuations in refractive index of air, just add math. Satellite imagery +math Lysimeter - measure the weight of a column of soil, im guessing dry soil is lighter. All of thoose sound like lots of money. A scintillometer seems doable as diy. For an area like a tree, I'd start with a laser diode ( i dont know which frequency, but as a complete guess id try infrared, possibly red, and stay away from green and blue), the other end would be either a phototransistor or a photocell. A low noise (probably high gain) amplifier and a quality anolog to digital converter (maybe a 24 bit sound card, probably a pi zero attached not an arduine or esp) This is all very speculative(pun intended) on my part, it could be completely wrong, i am guessing based on the few words in wikipedia. 
 
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 Hmmm. Looking up scintillometers, I see they are advertised as "large aperture", so you may need an array of photo[diodes,cells], which adds a lot of complexity, matching, summing etc,but maybe you could get away with a condenser lens. 
 

 
					
				 
					
				 
					
				

