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Question:

What is Landsat 7 ETM+ SLC-off data?

Answer:

Landsat 7 ETM+ SLC-off data refers to all Landsat 7 images collected after May 31, 2003, when the Scan Line Corrector (SLC) failed. These products have data gaps, but are still useful and maintain the same radiometric and geometric corrections as data collected prior to the SLC failure.

The Landsat 7 page provides information about the SLC-off data products.