Dear Muhammad, I haven't corrected MASTER data using FLAASH, but I thought I'd point out a couple of things you'll want to consider. First, MASTER data contains thermal bands, and FLAASH is not an appropriate tool for atmospheric correction of thermal bands. ENVI does have a tool that can be used for atmospheric correction of thermal data. That tool can be found under Basic Tools -> Preprocessing -> Data-Specific Utilities -> Thermal IR -> Thermal Atmospheric Correction. You can find more information about this tool in the ENVI Help system under ENVI User's Guide -> Basic Tools -> Preprocessing Utilities -> Data-Specific Utilities. So, it might be useful for you to consider different atmospheric corrections to the visible through shortware IR bands, and to the thermal bands. Second, the question of whether you need to apply any atmospheric correction to your data depends on what you're planning to do with the data. Some applications do require accurate atmospheric corrections (e.g., details spectral analyses), and some don't (e.g., visual or spatial analyses). I hope this helps. Peg