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The U.S. Geological Survey (USGS) has completed development of a major new product enhancement for Landsat 7 Enhanced Thematic Mapper Plus (ETM+) data captured after the Scan Line Corrector (SLC) anomaly.
Gap-filled product options will now allow the data merge of one or more SLC-off fill scenes for generation of a final gap-free image. Users may select from up to four SLC-off scenes, in addition to an optional SLC-on scene, to create a final data merged product.
The technique used to generate the new product is similar to the previous gap-filled products. The major advantage of this new product is a much improved temporal match of fill scenes used to produce the final image. The SCL-off to SLC-off product will now allow the use of scenes from consecutive passes to fill the gaps of the target scene.
The cost of the new SLC-off to SLC-off product option is $300 per scene. Data products that are generated using only Landsat 7 SLC-on data for the gap-fill (acquired prior to the SLC failure) will continue to be offered at the previous price of $275 per scene. Standard SLC-off products (with the data gaps included) or SLC-off interpolated products are also available for $250 per scene.
This new product represents a continuing effort by the USGS Landsat Project at the EROS Data Center in Sioux Falls, South Dakota to increase the utility of the Landsat 7 Enhanced Thematic Mapper Plus (ETM+) data affected by the non-functional scan line corrector. Previously released products designed to compensate for the scan line corrector problem include a fully interpolated option and an SLC-on to SLC-off data merge option.
The primary difference between an SLC-off Landsat 7 product compared to data collected prior to the anomaly will be the presence of duplicated data in the SLC-off image for Level Zero Reformatted ( L0Rp ) and Level One Radiometrically Corrected (L1R) data. In the case of a Level One Geometrically Corrected ( L1G ) product, the USGS processing systems use a variety of methods to replace the duplicated image data.
The total loss of image data has been estimated to be approximately 22% over any given scene. The maximum width of the data gaps along the edge of the image (or duplicated data, in the case of L0Rp/L1R) would be equivalent to one full scanline, or approximately 390 to 450 meters. The precise location of the missing scan lines will vary from scene to scene.
SLC-off Data Product: Level 0Rp
The Level 0Rp (L0Rp) SLC-off data product will contain alternating areas of duplicated scanlines (14 pixels wide) along the edge of the scene (Figure 1). Width of the duplicated regions will gradually diminish toward the center of the scene. The center of the image will contain nominal image data
Level 1G Standard – This product includes the original data gaps. Duplicated pixels have been replaced with null values (zero-fill) and the image will therefore contain alternating “stripes” of missing data. ($250 per scene)
Level 1G Gap-filled – This product provides a fully populated image, in which all of the missing image pixels in the original SLC-off image have been replaced with histogram-matched data values derived from one or more alternative acquisition dates. ($275/$300 per scene)
Level 1G Interpolated – Maximum (15-pixel) interpolation provides a fully populated image, in which all missing pixels have been filled with DN values interpolated from neighboring scan lines. Note that all replacement data values are derived from within the current SLC-off image. ($250 per scene)
Level 0Rp product, showing nominal image data at the scene center (Image Source: USGS)
Source: USGS LANDSAT Project