I'm trying to fuse SPOT 5 PAN and XS images and having trouble with the radiometric correction. I was hoping to obtain at surface reflectance as the fused image will be used for vegetation analysis. I was able to calibrate and preform a FLAASH correction on the XS image but cannot follow the same procedure for the PAN image as FLAASH requires a multiband input. Is there another (fairly accurate) model for PAN atmospheric correction? Or would it make sense to leave both images as radiance and preform the atmospheric correction after fusion?