Landsat 7 Instrument to Attitude Control System Alignment Update
Landsat 7 sensor alignment involves calibrating the spacecraft navigation base reference system, commonly referred to as the Attitude Control System (ACS), to the Landsat 7 Enhanced Thematic Mapper Plus (ETM+) sensor and its boresight. This calibration improves upon the geodetic accuracy of the imagery which in turn improves the accuracy of the Level-1 products.
Return to Collection 2 Level-1 Data Overview
Trending of geodetic accuracy results for Landsat 7 Collection 1 ETM+ data indicated a small linear, growing, misalignment between the attitude control system and the sensor’s boresight.
This update for Collection 2 affects scenes acquired between 2013 to 2019. (This update was implemented into Collection 1 processing for scenes acquired since late 2019; therefore, users may not find significant differences between the accuracy of Collection 1 and Collection 2 L1GT products acquired since late 2019.)
The updates to the Landsat 7 ETM+ sensor alignment are best illustrated by looking at the mean geodetic offset of the Landsat 7 ETM+ systematic imagery. The graphs below illustrate the along- and across-track mean, and root mean squared error (RMSE), grouped by quarters from late 2013 to early 2018, both prior to the update (Collection 1) and after the sensor alignment update (Collection 2). An upward trend in the across- track mean can be seen in the left graph prior to the update. This upward trend is not present in the results post sensor alignment update. Seasonal dependencies and site selection for the scenes used in this assessment causes a degree of variability in the measured mean and RMSE and is expected.
