The essential basic difference with 2-D data is that we are not looking to extract a region of the CCD frame into a single spectrum but wish to preserve the spatial direction in order to study changes in the spectrum with position.
Given this, the initial image preparation is the same as for 1-D data which is described in Image Preparation and Flat Fielding.
The order in which 2-D data is calibrated is different to that for 1-D data. Many of the tasks in processing the data (e.g. background sky emission line subtraction) require the 2-D frame to be correctly oriented with spatial and dispersion axes perpendicular.
As can be seen in the example arc line image (see the figure below for an example) the lines have a definite curvature along the spatial axis. This is due to the different path lengths the light takes through the optics along the slit. Correcting for this is carried out along with wavelength calibration.
Simple Spectroscopy Reductions
