yes you can follow the attached document, it will guide you how to use ERDAS for SEBAL. you can also download spreadsheet and software tool to help ET calculations along with ERDAS from the following link

http://extension.uidaho.edu/kimberly/tag/software/

Cheers!

Hi Shahzad Sultan,

Thanks a lot really appreciate your help.

Kind Regards,

Alois · 

you are welcome dear and If I remember there is a built-in package to apply sebal in ilwis (free software package)

Hi there

Why i can not access to this link:

http://extension.uidaho.edu/kimberly/tag/software/

The link is awaibalbe though not any specific info for METRIC or SEBAL... the page contains two links for calculating ET ref and ET with FAO56....try to open these (the same links):

http://extension.uidaho.edu/kimberly/2013/04/spreadsheets-supporting-fao-56-example-calculations/

http://extension.uidaho.edu/kimberly/2015/06/ref-et-reference-evapotranspiration-calculator/

The links  http://extension.uidaho.edu/kimberly/2013/04/spreadsheets-supporting-fao-56-example-calculations/

http://extension.uidaho.edu/kimberly/2015/06/ref-et-reference-evapotranspiration-calculator/

are not giving the spread  sheets supporting  FAO 56 and the calculator of ET