The implications of the spectrograph designs for calibration procedures and the complexity of data reduction will depend largely on details of their realisation. There are, however, some generic differences which carry implications for the scientific performance. These can be divided into the following categories:
The overall quality of the calibration will depend on mechanical and detector stability and on the overall levels of parasitic light within the instrument. There are likely to be significant differences between the behaviour of the IFS and MOS instruments. The IFS should be mechanically stable with no or few (at least for the LR channel) moving parts and a fixed focal plane configuration. The MOS has an active focal plane and most probably exchangable or moving gratings. The effects produced by a micro-mirror/shutter array in the focal plane will need to be well understood. While such a device has the advantage of being able to block bright sources from the instrument, the diffration produced by the regular grid of moveable elements may produce coherent patterns of parasitic light within the spectrograph.
An important issue which applies, in a generic sense, to both concepts is the coverage of the 1-5 micron band by one or two separate channels with different detector arrays. The noise performance of the detectors depends critically on their upper wavelength cutoff and the level of parasitic light depends on the bandpass of the channel.
The data reduction process is significantly different for the two instrument types. For the IFS, the geometry in the telescope and the spectrograph focal planes is known and stable while for the MOS, the spectrum extraction and wavelength calibration requires a precise knowledge of the field being observed.