The pipeline recipe that reduces LW spectroscopic data is called isaacp lw_spjitter and it uses an initialisation file, which contains parameters that define how the recipe runs. To generate one, type isaacp lw_spjitter -g lw_spjitter.ini at the prompt and this will create an initialisation file called lw_spjitter.ini. This file can be edited and modified by the user to setup some parameters.
The initialisation file contains parameters which indicate
The recipe first classifies the frames into the three frame types: int, hcycle1 and hcycle2. It then classifies the int frames according to offsets that are recorded in the header, i.e. frames of type A and type B, and subtracts frames of type B from type A. This removes the residual background very well. Images are then flat fielded. If the flat field is missing, the recipe skips the flat fielding step.
The list of combined images are corrected for slit curvature, wavelength calibrated, shifted and recombined together to form the final combined 2d spectrum. If possible, the wavelength calibration is done with the sky lines in the half-cycle frames. Otherwise, it uses a physical model.
Then, at the end, the spectrum is detected and extracted.