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6.2.1 Planning Imaging Observations
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FLITECAM Imaging observations can be obtained in two different modes: Stare (with or without dithers), and Nod-Off-Array. The choice depends on the target and astronomical background. Chopping is not supported with FLITECAM.
Stare mode observations involve a single telescope pointing centered on the source with dither pattern relative to it to facilitate background subtraction and image calibration. Dithering can be performed by selecting from pre-programmed dither patterns, or by defining a custom pattern. Observational experience has shown that stare observations without dithers are particularly challenging with FLITECAM due to thermal background issues. Therefore, we recommend using dithers with at least 9 points, parcuarly longward of 2.2 microns.
If the science target is extended or if it is located in a crowded region or region of extended emission, dithering alone may not be able to produce a suitable sky background frame. In this case the GI may elect to observe using Nod-Off-Array mode which will complete a dither on-source and then nod the telescope to a defined "sky" position and complete a dither there as well. Selection of the nod direction and amplitude depends on the field of view around the target and will need to be chosen carefully to access a clean "sky" position and allow proper background subtraction.
The observing efficiency for FLITECAM Stare mode observations with dithering is expected to be on the order of 70%. Observations in Nod-Off-Array mode are expected to result in a decrease in observing efficiency to around 35%. However, these efficiencies are built-in to the SOFIA Proposal Tool (SPT) and do not need to be specified by the GI.