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Definitive Ephemeris

By Landsat Missions

Definitive Ephemeris were used for geometrically correcting Landsat 7 data to 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.

Landsat 7 scenes were initially processed with predicted ephemeris shortly after acquisition, and were then reprocessed with Definitive Ephemeris one to two days later. 

Landsat 8 or Landsat 9 do not require definitive ephemeris, since the Payload Correction Data (PCD) for the satellites 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 each of the Landsat spacecrafts- is provided on the following pages: 

Section 5 of the Landsat 7 Data Users Handbook provides more technical information about Definitive Ephemeris and how it was used in Landsat 7 product generation.  

Definitive Ephemeris files became available two days after acquisition. Files can be accessed by choosing one of the options below.