SWS does not use spatial chopping, hence all spectra will contain some contribution by zodiacal light and galactic background. In most cases, this will be negligible compared to the source flux. The zodiacal background component is the most important over the largest part of the SWS wavelength range, with a continuous spectrum corresponding to a dust temperature of about 260K, that does not affect searches for line emission. As an order of magnitude estimate, a typical zodiacal light flux density seen within a SWS aperture will be about 0.3Jy. In some cases, e.g. for faint sources in regions of active star formation close to the galactic plane, it may however be necessary to consider mapping or taking an independent background spectrum close to the source via a concatenated observation (see the ISO Observer's Manual).