This isn't really an ENVI specific issue but nonetheless somebody might be able to help me as I am having real problems getting my head around this problem. As I want to compare image spectra with library spectra I need to atmospherically correct ASTER data; I have used a variety of ENVI tools to do this (flat field, log residuals) and also got AST_07 surface reflectances. As these surface reflectances have a variety of value ranges (both from dataset to dataset and for each band of the datasets) I have been scaling the datasets from 0-1 however, I am not sure whether this is a valid procedure. I have spent a considerable amount of time investigating whether this is the right thing. Investigating the spectral signatures of the datasets would seem to suggest that this is the right thing to do; spectral curves for the un-scaled datasets are very odd when compared to the scaled datasets. Some clarification would be greatly appreciated! thanks, Christian Haselwimmer