we first derived the rms level of the temporal fluctuations for each pixel of a given raster map, taking into account the overlap of the individual raster frames (each sky position in the map was observed on average in two independent individual frames). The resulting average rms noise per pixel depends on the level of the diffuse mid-IR emission in the raster, and thus varies from core to core. Typical values are $\sim$ 0.05 MJy/sr for regions with low mid-IR background (e.g. Taurus, Eastern part of the $\rho$ Oph complex) and $\sim$ 0.1 MJy/sr for regions with high mid-IR background (e.g. L328 and L310). This temporal rms noise however does not take flatfield noise (estimated to be $\sim$ 5%) into account and could be underestimating the total amount of noise. Another approach to estimating the noise in an image is by calculating the rms noise level of the spatial fluctuations over regions showing very little structure. By doing so, we a priori overestimate the noise level since we do not discriminate between true instrumental noise in the image and small-scale spatial structure in the (emitting and/or absorbing) source. The rms values listed in Table \[sources\] and the error bars used 