Sample spectra in OMC-3 field. Frame a shows the Herschel 250 μm map and the outline of the PACS coverage. The white circles indicate the reference area used for background subtraction. Frame b shows spectra for background-subtracted data at the positions marked in frame a with blue, magenta, and red circles. The data correspond to 1’ (solid symbols; Spitzer, WISE, Herschel) or 2’ resolution (open symbols; AKARI, with 30% error bars). The average spectrum over the PACS coverage is drawn with a black dashed line.