RIX Roy: IMprove background subtraction N-band

[hugobuddel]

Comment roy on 10.4.2:

"1) we will use a 3-point chopping pattern (VISIR uses a 2 point pattern)
2) this is very new info: we may do extensive spatial modulation (dithering) within a nod half cylcle; i.e. we do our 3-point chop
pattern a few times, then slightly move the central position and repeat the 3-point chop pattern, and do this n times in a nod-half
cycle (then do the nod and repeat the same pattern in the other nod position). This is to mitigate the (many) bad/hot pixels in the
GeoSnap array. We are still trying to get a better GeoSnap, but likely we will adopt this scheme regardless of what GeoSnap
exactly will be used (just that the dithering amplitude will depend on the individual device used)."

This would need to be updated in the N-band recipe section and perhaps in section 4 and 5 too