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andrewmovic Nov 14th, 2019 (edited) 101 in 8 days
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  1. <?php
  2. /* -------------------------------------------
  3. * Realtime Evapotranspiration Calculation  
  4. * Based on Penman-Monteith 56
  5. * Author: andrew@ugm.ac.id
  6. * Smart Agriculture Research Group
  7. * Department of Agricultural and Biosystems Engineering
  8. * Universitas Gadjah Mada
  9. * Created: 15 November 2019
  10. * ---------------------------------------------*/
  11.  
  12.  
  13. echo ("Realtime Evapotranspiration<br />");
  14.  
  15. $Temp = 25.35;
  16. $Rh = 89;
  17. //$Rs = 12.67;      // Watt/m2
  18. $Rs = 16.3;         // Mj
  19.  
  20. // Call the function
  21. $hitEto = ETo($Temp, $Rh, $Rs);
  22.  
  23. echo "ETo : " . $hitEto;
  24.  
  25. // ETO Function
  26. function ETo($Th, $Rh, $Rs){
  27.     /*
  28.     Input
  29.     Th - Temperature
  30.     Rh - Relative Humidity
  31.     Rs - Net Radiation
  32.     */
  33.  
  34.     // Initial condition and assumption
  35.     $Gsc = 0.0820;  // Solar time angle at midpoint
  36.     $U2 = 0.73;     // Windspeed, asmp. 2m/s
  37.     $dz = 25;       // Elevation
  38.     $dlz = 250;     // Center of timezone (UTC+7) bangkok
  39.  
  40.     #conversion Rs from Watt/m2 to MJ/m2 h
  41.     //$Rs = $Rs * 0.0036;
  42.     $Rs = $Rs * 1; // if already in MJ/m2
  43.  
  44.     // Saturation vapor pressure (kPa)
  45.     $eoa = 0.6108*exp((17.27*$Th)/($Th+237.3));
  46.  
  47.     print("eoa: ". $eoa. "<br />");
  48.    
  49.     // Actual vapor pressure
  50.     $ea = $eoa * ($Rh/100);
  51.    
  52.     // Vapor pressure deficit
  53.     $VPD = $eoa - $ea;
  54.  
  55.     $Rn = $Rs;          // Reading from sensor directly (net radiation)
  56.  
  57.     // Soil heat flux
  58.     if($Rn > 0) {
  59.         // day
  60.         $G = 0.1*$Rn;
  61.     } else {
  62.         // night
  63.         $G = 0.5 * $Rn;
  64.     }
  65.  
  66.     // Calculate Delta and Lambda and Gamma
  67.     // =4098*M2/((I2+273,3)^2)
  68.  
  69.     //$Delta = 4098*0.6108*exp((17.27*$Th)/($Th+237.3))/pow(($Th+237.3),2);
  70.     $Delta = 4098*exp((17.27*$Th)/($Th+237.3))/pow(($Th+237.3),2);
  71.  
  72.     print("delta: ". $Delta. "<br />");
  73.  
  74.     $Tk = $Th + 273.16;
  75.     $Lambda = 2.501-(pow((2.361*10),-3))*$Th;
  76.    
  77.     print("lambda: ". $Lambda. "<br />");
  78.  
  79.     // Excel bu Tining
  80.     // =101,3*(((293-0,0065*G2)/293)^5,26)
  81.     $P = 101.3*pow((($Tk - 0.0065*$dz)/$Tk),5.26) ;
  82.  
  83.     $Gamma =  0.00163*($P/$Lambda);
  84.     print("Gamma: ". $Gamma. "<br />");
  85.     $ETo = ( 0.408* $Delta*($Rn-$G) + ($Gamma*(37/($Th +273.16))*$U2*$VPD ))/($Delta + ($Gamma*(1+(0.34*$U2))));
  86.     print("P : ". $P. "<br />");
  87.     return $ETo;
  88.  
  89. }
  90.  
  91. ?>
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