FOR FREE
PET Calculator
A very small script that will calculate the potential evapo-transpiration(ET) with the help of Penman's Equation(PE).PE is a big equation and needs tedious and carefull calculations to find the ET.The calculator will calculate the ET in mm per day ,by PE, if the values of the following variables and constants are given :
With the help of above variables and constants the following will be calculated :
Ha : Incident solar radiation in mm of evaporable water per day outside the atmosphere on a horizontal surface
Ea : Parameter including wind velocity and saturation deficit
ET : Daily Potential Evapo-transpiration in mm/day
Cost : $ 0
Software developed by Mrinmoy Majumder
Completely online software - No need to download
Output depend wholly upon your input.
Constant
a : a constant that depend on latitude and is given by a = 0.29cos)
b : a constant with a value of 0.52
s : Stefan-Boltzman Constant
g : Psychrometric constant = 0.49 mm of mercury / degree centigrade
Variables
A : Slope of the saturation vapour pressure(ew) vs temperature curve at mean air temperature in mm of mercury per degree centigrade(See any books on Water Resources)
N : Actual hours of sunlight
n : Maximum possible hours of sunlight
r : Reflection Coefficient
Ta : Mean air temperature in degree kelvin(273 + C)
ea : actual mean vapour pressure in the air in mm of mercury
u2 : Mean wind speed at 2m above ground in km/day
ew : Saturation vapour pressure in the air in mm of mercury
