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Download Definitive Ephemeris

Definitive Ephemeris is used for geometrically correcting Landsat 7 data and provides improved accuracy over predicted ephemeris.

An ephemeris is a set of data that provides the assigned places of a celestial body (including a manmade satellite) for regular intervals. Definitive Ephemeris shows the position and velocity of the spacecraft at the time imagery is collected, and shows the position and velocity of the satellites in one-minute intervals.

Newly-acquired Landsat 7 scenes are initially processed with predicted ephemeris, and are reprocessed with Definitive Ephemeris applied within 1 to 2 days of acquisition.

There is no Definitive Ephemeris for Landsat 8, since the Payload Correction Data (PCD) for the satellite is very accurate. Telemetry information in the form of Two-Line Element (TLE) Set — which lists the orbital elements that describe the state (position and velocity) of the spacecraft — is listed on

Section 5 of the Landsat 7 Data Users Handbook provides more techicnal information about Definitive Ephemeris. 

Definitive Ephemeris files are available two days after acquisition, and can be accessed by choosing one of the options below: