Importing Landsat data into ENVI

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”.

Level 1 Image

ENVI can directly and easily open data in this USGS format.  Each data layer will end in …_T1_B1.TIF (or B2.TIF, B3.TIF, etc.).   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 should 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.

Level 2 Surface Reflectance Product

The Level 2 Surface Reflectance product has been converted by the USGS from digital numbers to surface reflectance.  Each data layer will end in …_T1_sr_band1.TIF (or band2.TIF, band3.TIF, etc.).  As of this writing the USGS  provides the original Level 1 metadata TXT file, which does not correspond to the supplied Level 2 data files.  As a result, ENVI cannot open these data files directly from the MTL.TXT file as it can with Level 1 data described above.  You must open each data layer individually, then create a layer stack, and finally save the result as a new file.

Open all 6 or 7 … _T1_sr_bandn.TIF files in ENVI as grayscale datasets.  In the Toolbox search box type layer to find the Layer Stack tool and open it.  Click on the Import button and add the 6 or 7 images.  Carefully check that the images are in the correct order, i.e. band 1 is followed by band 2, band 3, etc.  If they are not in the correct order click on the Reorder button and rearrange them.  Click OK and save this as a new ENVI file with a meaningful name such as the date in yyyymmdd.dat format.