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Question:

What is the geometric accuracy of a Landsat 7 ETM+ systematically corrected data product?

Answer:

Landsat 7 ETM+ was designed to provide a geometric accuracy of at least 250 meters (1 sigma) in low-relief areas at sea level. However, the use of definitive ephemeris for L1GS (systematic) correction frequently provides a geometric accuracy within 30-50 meters.

The .MTL field "EPHEMERIS_TYPE" displays either PREDICTED or DEFINITIVE.  Predicted ephemeris is applied immediately after data acquisition. Shortly after initial processing (about 1 day), the data are reprocessed using definitive ephemeris.

The Landsat 7 Image Assessment System (IAS) Geometric Algorithm Theoretical Basis Document provides more details about processing and geometric correction for Level-1G data products.