Two background corrections can be performed with the package:
Interorder background: The scattered light in the interorder region is measured at a certain number of positions and the background map is provided by polynomial or spline interpolation. Interorder positions can be visualized with the commands:
SET/ECH BKGVISU=YES
LOAD/ECHELLE
and the interpolation and background subtraction is performed using SUBTRACT/BACKGROUND. This command also update the image descriptors to avoid background subtraction to be performed again by the FLAT, RESPONSE or REDUCE commands.
Sky background: Sky windows are defined on both side of the orders with the comamnd DEFINE/SKY and sky background is extracted using EXTRACT/SKY. The extracted sky can be subtracted from the extracted spectrum like in:
DEFINE/SKY object 2 CURSOR
EXTRACT/SKY object sky FILTER
SET/ECHELLE EXTMTD=AVERAGE SLIT=8
EXTRACT/ECH object ext
COMPUTE/IMAGE sub = ext - sky