Operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Administration under Contract Nas5-03127 Title: Self –calibration and the Dither Patterns for Nircam and Miri

1.0 ABSTRACT NIRCam and MIRI have recently put together sets of imaging dither patterns that have been optimized for the anticipated science goals of each instrument. The MIRI set contains patterns that are explicitly optimized for self-calibration, whereas the NIRCam patterns are all optimized for sub-pixel resolution, L-flat mitigation, and gap coverage, without the explicit goal of self-calibration. A data set that is optimized for self-calibration is taken in such a way that the flat fields and/or the bias can be solved-for internally, without reference to formal calibration observations. There are circumstances where such a self-calibration can improve the final data quality. This document will describe why self-calibration is a relevant goal for MIRI, but not for NIRCam. 2.0 INTRODUCTION NIRCam and MIRI have recently put together sets of dither patterns that have been optimized for the anticipated science goals of each instrument (see Anderson 2009 for the proposed NIRCam patterns and Chen 2009 for the proposed MIRI patterns). The question has come up informally as to why MIRI has patterns that are optimized for self-calibration, whereas NIRCam does not. This document is an effort to address that question. We begin with a brief presentation of the dithering strategies devised for the two instruments. We will then give a brief description of the goals and requirements for self-calibration. Finally, we will discuss how the dither strategies for NIRCam and MIRI relate to self-calibration. 3.0 CURRENT NIRCam AND MIRI DITHER STRATEGIES In this section we will give an overview of the dithering strategies devised for NIRCam and MIRI imaging. Both instruments have divided their dithering strategies into primary