Dear Alex, For hyperspectral data like AISA, FLAASH does not use a spectral response function. Instead it uses the wavelengths (and FWHM if available) provided in the ENVI header file for the input data. ENVI itself, outside of FLAASH, doesn't have any particular requirements for radiance units. FLAASH requires radiance to be in units of µW/(cm2 * sr * nm), unless you provide a scale factor that when divided into the input pixel values results in units of µW/(cm2 * sr * nm). So if your input image has radiance units of W * m-2 * sr-1 * µm-1 (which is also W/(m2*sr*µm)), then you would need to provide a scale factor of . . . let's see . . . 0.01. You'll want to check my math on that. Unit conversions were never my strong point. The most common problem when running FLAASH is providing the wrong scale factor to convert the radiance units in the image into the units that FLAASH expects. - Peg Exelis VIS