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What are Landsat 7 SLC-off Gap Mask files?

Band-specific gap mask files are included with every Landsat 7 Scan Line Corrector (SLC)-off Level-1 data product. These ancillary data identify the location of all pixels affected by the original data gaps in the primary SLC-off scene.

The gap mask is provided as a series of individual band files, in compressed (GZIP) GeoTIFF format.


SLC-Off showing showing satellite image with parallel bands of missing image; and SLC-On gap mask with correlating blue bands.
Left: Sample SLC-Off image; Right: SLC gap mask

Gap Mask Legend Values:

  • green = primary scene
  • blue = fill scene 1
  • yellow = fill scene 2
  • pink = fill scene 3
  • red = no data (not filled)

For a standard SLC-off product, the data values contained within the gap mask file are:

  • Value of 0 - No data (data were missing in the original SLC-off scene)
  • Value of 1 - Populated data (data were present in the original SLC-off scene)

Learn more: Landsat 7 web page