===== Imaging N =====
Use case: //Dust continuum imaging in AGNs//

===== Operational procedure =====
==== Preparation ====
  * ETC
  * p2pp kind of OB preparation (including usage of ETC)


==== Acquisition ====

During the preset, the telescope is sent to the position of the target. The AO NGS is automatically centered on the WFS (no interaction needed). In case of the off-axis NGS (SEQ NGS ISTARGET = F), an internal WFS mirror (field selector) will be tilted such that the off-axis NGS falls exactly onto the WFS. The operator may be asked to perform fine centering of the target on the detector.

Template options: 
  * [[metis_img_n_acq|METIS_img_n_acq]]


==== Science sequence ====

In the N-band, the fluctuations of the thermal background and the detector noise require chopping (~1Hz for the GeoSnap detector). Since the simple subtraction of two chopped frames (on- and off-axis positions) leaves chopping residuals, we additionally need to regularly offset (nod) the telescope. 

Template options: 
  * [[METIS_img_n_obs_genericchopnod|METIS_img_n_obs_GenericChopNod]]


===== Required calibrations =====
  * Sky background subtraction via chopping or dithering (dependent on the detector) or drift scanning (tbd) and nodding
    * Associated pipeline recipes ''chop-difference frames'' and ''nod-difference frames''
      * subtract sum (median?) of sky frames from sum (median?) of target frames for each nod position to produce chop-difference frames
      * subtract the sum of all nod A positions from the sum of all nod B positions to produce nod-difference frame
  * flux calibration (sky atmosphere modeling + one/few standard observations per night?)
    * Associated pipeline recipe ''flux-calibrate IMG_N''
      * applies (previously determined) flux conversion factor to raw counts of the nod-difference frame to produce background-subtracted, flux calibrated image (cube?)
  * PSF re-construction(?)

===== Science data products =====
  * background-subtracted, flux-calibrated image (cube, tbd). Units: [photons/s/pix] (tbc)
  * corresponding uncertainties (cube)
  * PSF (cube)

===== Discussion =====
 [[img_n_discussion|img_n_discussion]] 