You have to loop through each band. Have a look at this tech tip: http://www.ittvis.com/ser...echtip.asp?ttid=3893

Dear Sir, Thank you so much for ur reply. But, the loop shows running the band math with same values of variables on the input image. In my case, I will have to substitute different values of top of atmosphere solar irradiance on different bands. The bottom line is 'each band has a different value'. THe formula is this Radiance = (reflectance * cos(solar zenith angle)* (top of atmosphere solar irradiance ))/(pi*d^2) Keeping all other variables (except reflectance ) constant I will have to change top of atm. solar. irr for each band. So can U suggest me how can I proceed on this ? I have got my values in excel file. For example, in erdas we insert a custom table in model maker. Likewise can I insert the excel file in the code such that for each iteration , my value keeps altering? Regards, Aishwarya.