Landsat Missions

SLC-off Data Products: Level 1G, 1Gt, and 1T Gap-filled

The Level 1 corrected gap-filled Scan Line Corrector (SLC)-off products are derived data products, in which all of the missing image pixels in the original SLC-off image are replaced with histogram-matched data values from one or more Landsat 7 scenes from separate acquisition date(s). This technique results in a fully populated “wall-to-wall” image product. For optimal results, the images chosen to generate a gap-filled product should be from the same season and contain minimal transient data such as clouds, snow cover, or fires. Areas with low temporal variability with respect to land/surface cover will also produce the best results when generating this product.

There are two processing methods by which a user can fill in the areas with missing pixels: SLC-off to SLC-on or SLC-off to SLC-off gap filling. When ordering a gap-filled product, the user may select up to four SLC-off scenes and/or a single SLC-on scene (prior to May 2003) to create a final data-merged product.

Figure 1 illustrates the edge portion of an original SLC-off scene after Level 1 processing. Figure 2 illustrates the same location after gap-fill, using histogram-matched data from a previously acquired SLC-on scene with equivalent seasonality.

The histogram-matching technique chosen by the United States Geological Survey (USGS) Earth Resources Observation and Science (EROS) consists of a localized linear transform performed in a moving window throughout the missing pixel region. Histogram matching is a procedure that is often used to correct striping or banding in imagery, and it can be applied in a similar fashion to fill the scan gaps in SLC-off data. For each of the input scenes, data in the scan gap region will be locally histogram-matched to the SLC-off primary scene, thus transforming the previously acquired scene (SLC-off or SLC-on) data into equivalent values for the SLC-off scene. The transformed data are then used to replace the missing pixels. Please see the gap-fill methodologies for detailed information about the histogram matching procedure:

The gap-filled SLC-off product that is delivered to the user includes the final gap-filled image and the Gap mask (one file per band) NOTE: The original ("primary") SLC-off scene and the original ("fill") SLC-off and/or SLC-on scenes will not be included in the final product.

To download samples of the USGS gap-filled products, see the Sample Products page.

All SLC-off data products may be searched and ordered through EarthExplorer or the USGS Global Visualization Viewer (GloVis)

The distribution of Landsat 7 ETM+ L1Gt and L1T Terrain correction data is restricted to U. S. Government and its affiliated users. Please contact USGS EROS Customer Services if you have questions regarding this policy.

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Page Last Modified: May 12, 2008


Figure 1. SLC-off image (path 39, row 37, acquired Sept. 17, 2003)	Figure 2. Same image, with gaps filled by local linear histogram-matched data acquired Sept. 14, 2002