U.S. Analysis Ready Data (ARD) uses Landsat scenes that are placed into Collection-based tiers (Tier 1 and/or Tier 2).
Newly-acquired Landsat 7 ETM+ and Landsat 8 OLI/TIRS data are processed upon downlink but use predicted ephemeris (Landsat 7), initial bumper mode parameters (Landsat 7), or initial TIRS line-of-sight model parameters (Landsat 8), and the data are intially placed into the Real-Time Tier, which is not used in ARD processing.
- Landsat 7 ETM+ acquisitions are processed immediately using predicted ephemeris and initial bumper mode parameters and placed into the Real-Time tier. Shortly after initial processing (about 1 day), the data are reprocessed using definitive ephemeris, but remain in the Real-Time tier. During a period of instrument trending/characterization (about 26 days), calibration parameter adjustments finalize the geometric correction model, and the data are reprocessed and placed into either Tier 1 or Tier 2.
- Landsat 8 TIRS data may not meet specifications for co-registration with OLI. TIRS line-of-sight model parameters are refined based on data acquired during biweekly calibration maneuvers and scenes are reprocessed within 14 to 16 days of acquisition and placed into either Tier 1 or Tier 2.