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This method is designed to modify neighboring pixels in a single Landsat 7 SLC-off scene, creating a final aesthetic image only - no scientific analysis accuracy is guaranteed using this method.

This method was designed using ERDAS Imagine 2014™*, along with ENVI™* or Adobe Photoshop 2017™ * for final filled-image verification. The approximate time to complete a scene is 20 minutes.

Questions about this method can be sent to Customer Services.

*Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Preparation:

  1. Download and extract the Landsat 7 SLC-off image that will be used.
  2. Within the directory of the downloaded scene, create a new folder titled "Bands."
  3. Copy all band.tif files that will be used into the "Bands" folder. (Figure 1)
    (Exclude thermal band files B61 and B62 and the panchromatic band file B8. If the scene will be pan-sharpened, include B8. Band 8 gap-filling can be done using only Band 8*)

Landsat 7 image files in "Bands" folder
Figure 1: ERDAS Layer Stack

Process One: Creating Layer Stack

  1. Open ERDAS Imagine 2014
  2. Open the Layer Stack Tool (Select the Raster tab --> Spectral --> Layer Stack)
  3. Choose your Input band files and an Output File name that indicates this is the original data stack (ex. original_stack.tif) (Figure 2)


Figure 2: ERDAS Layer Stack

  1. Click OK. The Modeler will create a new layer stack. This process should take about 1-2 minutes.
  2. When the process shows “DONE”, click Dismiss and Close (Figure 3) 

ERDAS Process List
Figure 3: ERDAS Process List

*To gapfill panchromatic Band 8, follow the above steps, only using Band 8, saving with "_pan.tif" to differentiate between the multispectral files created.

Process Two: Initiate Filling Method (see Figure 4)

  1. Open the Focal Analysis Tool (Select the Raster tab --> Spatial --> Focal Analysis)
  2. Choose the original_stack.tif file created in Process One as your Input File.
  3. For you Output File, use a name that will designate the first pass of filling (ex. take1.tif).
  4. From the Focal Analysis Tool, change Data Type Output to "Unsigned 8 bit".
  5. In the Function Definition section, make sure Function is set to "Mean" and the "Ignore Zeros in Stats" option is checked.
  6. From the dropdowns, select "Ignore specified value(s)" and "Apply only at specified value(s)". (The values in both should be "0")

Focal Analysis Tool
Figure 4: Focal Analysis Tool Specifications

  1. Click OK. The Modeler will run the first pass of filling. This process should take 1-2 minutes.
  2. When the process shows "DONE", click Dismiss and Close.
    Repeat steps 1-7 up to five or six times, each time replacing the Input File with the previously created Output File. For example, the next filling pass will use “take1.tif” as the Input File and the new Output File would be named “take2.tif”

Process Three: Review Filled Imagery

After completing Process Two, it is important to compare pre- and post-filled imagery. ERDAS can be used to view both the original data stack (original_stack.tif) and the final gap-filled file (take#.tif).

Method One: Side-by-Side View (Figure 5)

  1. In the 2D View window, select the Open Raster Layer Icon and open the "original_stack.tif" file.
  2. From the Multispectral tab, select which bands you would like to display in the Red, Green, and Blue channels. Bands 4, 3, and 2 are the default. (Since Band 6 was not included initially, Band 7 data are actually displayed as "Layer_6")
  3. Select File --> New --> 2D View, then select the Open Raster Layer Icon and choose the final gap-filled file (take#.tif).
  4. Select which bands to display in the Red, Green, and Blue channels from the Multispectral tab to match the bands selected in Step 2.
    (This method is used to compare the non-filled and filled scan lines between the original and final images. You may need to alter the image's strech settings if you want the colors to match exactly)

ERDAS Side-by-Side Comparison
Figure 5: Side-by-Side Comparison in ERDAS

 

Method Two: Blend, Swipe, and Flicker Transitions

  1. In the 2D View window, select the Open Raster Layer Icon and open the "original_stack.tif" file.
  2. From the Multispectral tab, select which bands you would like to display in the Red, Green, and Blue channels. Bands 4, 3, and 2 are the default. (Since Band 6 was not included initially, Band 7 data are actually displayed as "Layer_6")
  3. Select Open Raster Layer Icon again and open the final gap-filled file (take#.tif)
  4. From the Multispectral tab, select the bands you would like to display in the Red, Green, and Blue channels that match the "original_stack.tif" image from Step 2.
  5. Right-click on your 2D View Layer in the Table of Contents and choose "Blend", "Swipe", or "Flicker" (Figure 6). These options toggle between the two images using different transition types to highlight the changes between the original data stack and the final gap-filled image.
    (These transitions are used to compare the non-filled and filled scan lines between the original and final images. You may need to alter the image's strech settings if you want the colors to match exactly)

ERDAS Transition Options
Figure 6: ERDAS Transition Options

Process Four: Finalizing Image for Use in Non-Scientific Venues (Photoshop 2017 without geographic extensions)

Photoshop can also be used to create a final image for use. However, using this method will not create a georeferenced image. See Section Five for using ENVI to create a georeferenced final filled image.

  1. Open the latest "take#.tif" file in Photoshop. The file will open as a grayscale stack.
  2. Select the Channels tab, open the extra options menu, and select Split Channels (Figure 7) (This will create individual grayscale images for each band in the stack)

Photoshop Channels Options
Figure 7: Photoshop Channels Options

  1. To create a color composite, select the Channels tab again, expand the extra options, and choose Merge Channels.
  2. In the Merge Channels dialog box, change Mode to "RGB Color" and Channels to "3" (Figure 8)

Merge Channels Box
Figure 8: Merge Channels Box

  1. The Merge RGB Channels box will appear. Specify which bands you want to occupy the Red, Green, and Blue Channels. *Band 1, by default is set to the "take#.tif_Gray" band. Band 2 will be "take#.tif_Alpha 1", Band 3 will be "take#.tif_Alpha 2", and so on (Figure 9).

Merge RGB Channels
Figure 9: Merge RGB Channels

  1. Click OK and the resulting image should be a color composite using the specific bands you selected.
  2. Save final image as desired

Process Five: Finalizing a Georeferenced Image for Use in Non-Scientific Venues (ENVI)

ENVI can be used to create a georeferenced final filled image

  1. Open ENVI
  2. Select File --> Open Image File, and choose the final filled SLC-off image (take#.tif)
  3. In the Available Band List box, the individual bands will be displayed (Since Band 6 was not included intiially, Band 7 is called Band 6 in the list).
  4. Select the RGB Color radio button
  5. Select which bands you would like to occupy the appropriate channels (Red, Green, Blue)
  6. Click Load RGB to display the filled image in the desired RGB channels.

Available Bands List in ENVI
Figure 10: Available Bands List in ENVI

  1. When the desired RGB composite is achieved, select File on the Image display box and choose Save Image As --> Image File.

Saving Image in ENVI
Figure 11: Saving Image in ENVI

  1. Make sure the Output File is TIFF/GeoTIFF and click Choose to navigate to the correct directory to save the final .tif image. Click OK. (A .tfw file will also be created that contains the georeferencing information).