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Mirror rotation correlated noise

Description

The relative differences of the MODIS dn response versus scan angle (RVS) between the two mirror sides change at different instrument electronic configurations for some of Terra MODIS TEB bands. This characteristic is called the mirror side correlated noise (MSCN). Obvious changes due to the MSCN are observed for bands 33 to 36.

Impact to L1B Data Set

This effect causes calibration biases and mirror side striping in the early mission before 2002/09/17, a time when three different electronic configurations (A1, B and A2) were used, whereas the current electronic configuration is A/B. The biases can reach 1% at large scan angles.

Estimated Impact to L2 Science Products

Science research with data in the early mission will be impacted until the biases can be corrected.

Cause of Effect

The Terra MODIS pre-launch tests did not have sufficient data sets to derive the TEB RVS. Therefore, two deep space maneuvers were conducted during March and April 2003 to derive the RVS. This characterization was applied to the entire mission. These deep space maneuvers were conducted at A/B electronic configuration on Terra MODIS. Because there are no corresponding RVS results for other electronic configurations used in the early mission, the RVS characterization could incur increased uncertainty when applied to other electronic configurations.

Mitigation Approach/Added Testing to Characterize Effect

Striping due to mirror side differences can be mitigated depending on the availability of MODIS observations when the instrument nadir aperture door is closed. This approach can adjust the RVS of one mirror side by minimizing the observed door temperature differences between the two mirror sides. However, this method does not correct the absolute biases caused by the RVS dependence on electronic configuration.

Estimated Schedule to Complete

No further action is proposed.

History of Characteristic

Historically, two adjustments to the RVS of mirror side 2 were performed in Collections 3 and 4 before the deep space maneuvers conducted in March and April 2003. After the RVS results were derived from the deep space maneuvers, they were applied to produce Collection 5 (and later) L1B data products for the entire mission. MSCN studies have been documented in internal memos M974, M977, and M1062.