Hi Volkanyilmaz, 1) Calibration and atmospheric correction are two different things. Calibration converts the original pixel values to values of radiance. Atmospheric correction then removes the effects of the atmosphere from those radiance values. 2) I don't know much about how the Hyperion data are distributed, but I can't imagine that it would be already atmospherically corrected. Atmospheric correction is something that is different for every scene, and is usually done on hyperspectral images by the end user of the data. 3) I don't think that any of the auxilliary files you mentioned have anything to do with atmospheric correction. 4) If you are applying an atmospheric correction to the whole image (all bands), then all of those bands will need to use the same units. If you plan to apply an atmospheric correction like FLAASH (in ENVI's Atmospheric Correction Module), then all of the bands will need to be calibrated to radiance. So, if you can't calibrate the uncalibrated bands, you would want to leave them out of the FLAASH atmospheric correction. - Peg

First of all, thanks for your reply Peg, you helped me a lot I wonder if there is a way of understanding an image is atmospherically corrected or not? If the image is corrected atmospherically it means that I don't need to do this. The scale factors that are used to convert the original pixel values to radiance values are 400 (for the first 70 bands) and 800 (for the bands from 71 to 242). Is that right? I've read somewhere that factors are 40 and 80. Which ones are right?

I've also had some confusion in this area. It appears that USGS updated the way in which they distribute their data for Hyperion. When you download Hyperion data you have the option of downloading a HDF or Geotiff file, this was down after some of the instructions were published (those mentioning 40 or 400 and 80 or 800 scaling factors). I've had more luck working with the Geotiff's for some reason. In all the literature that I've read, you need to preform an atmospheric correction. That is a user defined process that requires information about the scene.

I can't imagine that you would be given Hyperion data that are already atmospherically corrected. The individual user is almost always expected to apply their own atmospheric correction. To be sure, you could ask the data provider. Or, you could look at spectra from the image, and see if the solar curve, and atmospheric absorption features, have been removed. For example, see figure 6 on this web site for an example of what the solar spectrum looks like: http://telstar.ote.cmu.ed...s2/all_atmos_sys.htm I hope that helps. Peg

hello peg, i want to implement and compare the results of ATCOR, ACRON and FLAASH atmospheric correction methods. can u tell me how we can implement ACRON and ATCOR in ENVI 4.7.