Left: factor by which background subtraction reduces en-route drift (red), long-duration RFI (green), large-scale astronomical signal (blue; see Section 3.3.4), elevation-dependent signal (purple; see Section 3.3.4), and short-duration RFI (black; see Section 3.6.2) in our simulated data for background-subtraction scales of 3, 6, 12, and 24 beamwidths (dashed curves). Factor by which background and RFI subtraction (see Section 3.6) reduce these contaminants (solid curves). Right: fraction of the noise level to which these contaminants are reduced. If nothing is plotted, the contaminant is completely eliminated on this scale. For these measurements, each contaminant was simulated separately and in the absence of sources.