Monitoring Image Alignments and Flat Fields for AIA/SDO Data Images

The images from the 4 telescopes on the Atmospheric Imaging Assembly (AIA) on board the NASA Solar Dynamics Observatory (SDO) have different offsets (from sun center), plate scales, and absolute rotations that can be measured and corrected for accurate alignment. The most variable of these is the offsets presumably due to small thermal flexings of the telescopes. Here we describe the techniques used to make these measurements and show how the image alignments vary with time. Weekly measurements are made as part of the data monitoring that capture much of the drift in the geometric corrections but shorter time variations of typically a pixel also exist in the offsets. Angles and scales have much better short term stability. We hope to eventually capture these variations for the mission or at least provide software for end users.

We also describe progress made in determining flat fields for the 10 wavebands and show how these have been varying over the mission to date.

This work was supported by NASA under the SDO/AIA contract NNG04EA00C.