Hi Juaneras,
For SPOT try the tool available on the ITTVIS Code Contribution site. It's called 'spot_radiance.sav'
You might find something here as well:
http://ntrs.nasa.gov/arch...19230_2006011209.pdf
By the way where did you search for your formulas? Did you try Google?
Anyways, hope you find what you need.
Ciao