A slice across the Galactic plane at ℓ = 30.51° of the SPIRE 500 μm image, demonstrating the cirrus emission removal method. The top panel shows the 500 μm data with the background fits (solid gray: first iteration Gaussian fit to the smoothed background, dashed gray: first iteration convolved background, solid black: same as gray, final iteration, dashed black: same as gray, final iteration). Note that the final background (dashed black line) fits the low-lying diffuse emission nicely, including its asymmetry about b = 0°. The bottom panel shows the final background subtracted science image cut along the same Galactic longitude, with the final source cutoff drawn as a dashed black line at 65 MJy/sr.