Landsat data provided by the USGS are distributed as a single file in an archived and zipped “.TAR.GZ” format. These files must be extracted and uncompressed before you can use them.
After downloading a file move it to a separate folder in your user section of the server. Double click on it to load the program 7-Zip, showing the “.tar” file. Right-click on the “.tar” file and select Open Inside to display the detail data files. Click on the blue Extract icon and select the destination folder to extract the individual files that comprise the entire image. Each data layer is a separate TIF image file. There are also two text files with the same base filename but ending with _GCP.TXT and _MTL.TXT. This file structure is referred to as “GeoTIFF with Meta data”.
You can open each data layer individually, then create a layer stack, and finally save the result as a new file. This can be a time-consuming and error prone process. Fortunately ENVI can directly and easily open data in this USGS format. From the ENVI main menu select File | Open and navigate to the _MTL.TXT file. ENVI will automatically open the Landsat image with all bands in the correct order. The reflective bands are placed in one file, the thermal band(s) in another file. There will be a 15m panchromatic file for ETM and OLI sensors and a 30m Cirrus file for the OLI sensor.
While you can work with these data as they are, ENVI has only created a temporary virtual layer stack that is constantly resampled as you move around the image. You need to save each file as a new dataset. From the ENVI main menu select File | Save As, pick the file you wish to save, and in the Save File As Parameters dialog select the Output Format ENVI. Then in the Output Filename box navigate to your work area and enter an appropriate file name. Once this is saved as a new file, the uncompressed “.TIF” files and the “.tar” file can be deleted.