[GRASS-user] Evapotranspiration Estimation

[Ghansah, Benjamin (IWMI-Ghana)]

Dear Sirs,
Please I am estimating evapotranspiration (i.evapo.pt) from satellite imagery using GRASS 7.0.2. However, I have the following concerns that I will be glad if you could help me solve:


1.       I used the relation i.evapo.pt [-z] net_radiation=name soil_heatflux=name air_temperature=name atmospheric_pressure=name priestley_taylor_coeff=float output=name

I have image file of the net_radiation, soil_heatflux, air_temperature  (Which I assume is the same as the surface temperature)


The priestley_taylor_coeff  constant 1.26 is used.



However, I don't know how to compute or derive a map for the atmospheric_pressure

Can you help me out with it?



2.       I also computing the sensible heat flux ( i.eb.hsebal01)

I have successfully obtained all of the other parameters except the aerodynresistance.

I will be glad if you can direct me on how to obtain this also


                Thank you,


Best regards

Benjamin Ghansah

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