This post refers to the Tech tip ID 4114. I have some ASTER data processed to Level 1A, 1B and the orthorectified 3A1. I want to atmospherically correct the data using FLAASH. The tech tip explains that ENVI automatically applies calibration coefficients when opening level 1A and 1B according to EDC DAAC guidelines. This is however not performed on the level 3A1 data. When opened as (HDF EOS format) the data are simply scaled to 8bit 0 - 255 and not physical radiance units. I would therefore like to know how one goes about converting the Level 3A1 8bit scaled data to radiance units? Is it suitable to simply apply the following equation (DN value - 1) * Unit Conversion Coefficient Or should I also apply the gain and offset values using c1 * DN / c2 + c0 The unit conversion coefficients are contained in the 3A1 HDF header but are not applied ( the HDF format is version 4) when opening in ENVI. I am using ENVI 4.3 on a windows XP machine. Your thoughts and input on this matter are greatly appreciated Wesley