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Landsat 7 ETM+ Focal Plane Adjustments for Improved Band Alignment

By Landsat Missions

Landsat 7 ETM+ band alignment calibration involves determining band-to-band misregistration and new focal plane locations for each band, and then incorporating the updated numbers into Landsat Collection 2 Level-1 data processing.  

Return to Collection 2 Level-1 Data Overview

 

Trending of individual band registration accuracy for Landsat Collection 1 Landsat 7 ETM+ data indicated some cold-to-warm focal plane misalignments.  These misalignments were not constant throughout the mission but were affected by major events during the Landsat 7 ETM+ mission — these include the Scan Line Corrector (SLC) failure to Bumper Mode Operations in 2003, Bumper Mode Operations to the launch of Landsat 8 in 2013, and the launch of Landsat 8 to present.

Offsets were found only in Bands 5, 6, and 7; these were the only bands adjusted for Collection 2. 

The graphs below illustrate the registration displacement observed in Collection 1 Bands and 7 data, compared to the Collection 2 result after the adjustments were made. The misregistration prior to updates is shown in the left graph, while what can be considered the post-calibration residual error is shown in the right graph. The graphs illustrate the results segmented by time frame of the adjustment:

  1. Launch to SLC failure - April 15, 1999 to May 31, 2003
  2. SLC Failure to Bumper Mode - June 1, 2003 to March 31, 2007
  3. Bumper Mode to Landsat 8 launch - April 1, 2007 to May 31, 2013
  4. Landsat 8 to present - June 1, 2013 to present
Landsat 7 ETM+ Focal Plane Adjustments for Improved Band Alignment
Sources/Usage: Public Domain. View Media Details

Since the only bands demonstrating a measurable offset with respect to the panchromatic band (which is used as a reference for the sensor band alignment) were Bands 5, 6, and 7, this adjustment represents a change to the cold focal plane with respect to the warm focal plane of the Landsat 7 ETM+ instrument. Band 6 is adjusted based on the measured registration of Bands 5 and 7, then scaled according to the ratio between the Instantaneous Field of View (IFOV) of the bands. 

One 30-meter Landsat 7 ETM+ pixel has a nominal IFOV of 42.5 micro-radian, therefore the adjustment made to the band alignments represents a change of less than 0.1 pixel.  While this adjustment is measurable, it is less than the 0.28 pixels requirement allocated to the cold to warm focal plane budget. These results are based on the Collection 1 processed Landsat 7 ETM+ data; calibration adjustments for the Landsat 7 ETM+ band alignment prior to the creation of the Collection 1 archive are not  represented.