The command BACKGROUND/SMOOTH enables to define the background without previous order definition. This feature is useful for example to correct for the background the image required for the order definition. This command involves an iterative algorithm which performs the following operations:
A more elaborated scheme is required if the contribution to the background from adjacent orders is important, this occurs when the distance between orders is small. All above methods are implemented in command BACKGROUND/ECHELLE and selected by the echelle keyword BKGMTD.