Pre-processing

All raw data should be pre-processed in the following ways before processing with ECHOMOP:

  -  Ensure that the frame is stored in a Starlink-standard
     sdf file in an NDF array .DATA_ARRAY (the CONVERT suite
     of tasks provides image format conversion facilities).

  -  Rotate the data frame 90 deg. if necessary to achieve an
     orientation where the long axis of each order is
     in the X-pixel (horizontal) direction.

  -  Subtract the bias current value from all raw frames using
     the appropriate KAPPA or FIGARO command.

  -  Do not multiply CCD frames by the prevailing ADU-to     electron conversion factor prior to reduction.  ECHOMOP
     tasks prompt for this value and use it to generate resulting
     spectra with counts in photons.

If a cosmic ray contaminated frame is to be used for tracing the paths of the orders across the frame then

  -  Use ech_decos1 to clean cosmic rays from the trace frame.
     Note: this task flags cosmic rays in a quality array and
     does not actually alter any of the data frame values.
     This is the recommended approach in this situation.  The
     ech_decos1 task may be used stand alone, or it may be
     invoked from the main task by setting TUNE_CRTRC=YES at
     the start of a reduction.

  -  If you have many `identical' object frames then these may
     be processed together to provide a more reliable cosmic
     ray rejection.  The command procedure

        $ECHOMOP_SOURCE/decos_many

     provides this facility and should be the preferred method when
     multiple frames are available.  The procedure calculates a
     median image and then rejects pixels which deviate by more than
     n sigma from the median value (note that this means that all
     the frames must be of equal exposure time).  Bad pixels are
     flagged by placing values in the quality array of the frame
     concerned.