previous observation. For a few dense cores (L1672, SA187, and GF5), the field contained strong IRAS point sources and a shorter (0.28s) integration time per read-out was adopted in order to avoid saturation on the camera detectors. In these cases, the number of read-outs was 44 at each raster position and the total area mapped was $19.7\arcmin \times 18.8\arcmin$ for L1672 and SA187. In addition to the existing LW2 (5–8.5 $\mu$m) and LW3 (12–18 $\mu$m) maps of Abergel et al. (1996, 1998) with 6$\arcsec$ pixels, we took two new images of Oph D in the filters LW6 (7–8.5 $\mu$m) and LW9 (14–16 $\mu$m) with a pixel field of view of 3$\arcsec$. The Oph D field was covered by a raster of $6 \times 3$ images with an overlap of 22 pixels in both directions. The raster was tilted by 20$\degr$ with respect to the Celestial North in order to follow the core’s elongation (see Fig. 2d of MAN98 and Fig. 1 of Abergel et al. 1998). For these images of Oph D, 15 exposures were taken at each raster position with an integration time of 10 sec per read-out. The total area covered was $2.6\arcmin \times 4.1\arcmin$.

### Data reduction

