Assessment of the modis scan mirror on-orbit response changes

The MODIS instrument on NASA's Terra and Aqua spacecrafts is a multispectral radiometer with a whiskbroom scanning design, using a two-sided scan mirror as the primary Earth-facing optical element. Accurate characterization of the on-orbit changes of both sides of the scan mirror is crucial to the calibration of the Level 1B data products. This paper reviews the performance of the Terra and Aqua MODIS scan mirrors over the missions for both the reflective solar and thermal emissive bands, including degradation in gain and response versus scan angle, and differences between the two mirror sides. Particular attention is given to a recent electronic reset event experienced by Terra MODIS in 2022 that led to changes in the zero-signal bias and gain characterization between the two mirror sides. Calibration algorithm changes were made to mitigate the impact of this event, leading to reduced mirror side striping in the Earth scene imagery.