I do not understand exactly what the problem is. Perhaps you can clarify? Is the problem that you cannot read back into another ENVI session the NDVI image that you made in another ENVI session? Or is the problem that you do not know how to apply the equation that you have for emissivity? If the problem is understanding how to apply your equation, it may help if you can tell us what the equation is. Regards, Peg

Thanks for your reply: The problem that I do not know how to apply the equation that I have for emissivity? More explanation: Like I said before, I generated NDVI file, the next step I want to apply my equation. In other words I have to read NDVI file pixel by pixel as I guess and depending on NDVI value of that pixel I have different equation to be applied. The emissivity equation should be applied to every pixel of the image. you can find the equation in: http://www.umbc.edu/rssip...GARS.LandSurface.pdf it is in page 318, equation (8), ndvis is 0.2, ndviv is 0.5 Thanks

In general, you can apply equations like this in ENVI using Band Math. See the docs for Band Math here: http://www.harrisgeospati...BandMath.html#Enter. You will need to use conditional operators ("gt" for greater than, etc.) to determine which pixels meet which criteria for one equation. If you need to use several lines of IDL code to get the whole algorithm implemented, you can form that into an IDL function. If you then put that function into your ENVI or IDL path (for example, by putting it in the ENVI save_add directory), IDL will restore it when ENVI starts. It will then be available for you to call as part of your Band Math expression. Regards, Peg

Thank you very much I appreciate your help. I will work on it, and let you know