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Knowledgebase: IRAC
How should I decide which dithering pattern to use for a given IRAC observation?
Posted by Seppo Laine on 21 November 2008 11:52 AM
You want to select the dither pattern in such a way that every part of your target that is of interest to you will be imaged at least three times. If your object has spatial variations on a certain large scale, you will want to select a large enough dither pattern to enable you to separate these variations from the flat-field/sky dark variations of the instrument. If you plan to attempt superresolution, use the appropriate subsampling size (1/2, 1/3 or 1/4 pixel) together with a medium scale size dither pattern. For sources with a size similar to array size, use a small map with a large or medium-scale dither pattern. The small cycling dither pattern should only be used in conjunction with mapping as the small offsets alone are insufficient to move bright stars out of the straylight zones. If observations (AORs) in your program may be scheduled consecutively, they may produce residuals which would impact your science. In that case, we suggest using different starting dither positions if using the cycling dither pattern. For other (fixed) dither patterns, you can achieve some measure of randomization by converting fixed targets to cluster targets with a few pixel offset from target to target. Make sure you check the observe offsets only box in the AOT template in Spot if you use this strategy.

For more advice on IRAC dithering, please see examples in the Spitzer Observer's Manual (SOM) and read the IRAC dither section in the SOM carefully.