5 Conlusions

We have presented in this paper the final FIRBACK data reduction using: (1) The Phot Interactive Analysis version 7.2.2 and (2) extra developments (corrections of the flat-field, long and short term transients, transients induced by cosmic rays and adapted reprojection). Most of these extra developments have been made possible by the perfect redundancy inside each raster (one pixel overlap in both Y and Z direction). We have then checked the absolute calibration using PHT25 measurements and the footprint measured on Saturn (compared to the footprint model). We have shown that the ISOPHOT 170 $\mu$m extended emission calibration has to be corrected by a factor 0.89, which comes from the difference in solid angle between the PIA v7.2 and the modeled footprint.

Using this data reduction and calibration, we obtain an absolute calibration which is in remarquable agreement (better than 10$\%$) with brightness extrapolation that uses DIRBE data and HI column density measurements. We have in FIRBACK fields a very high signal to noise ratio (greater than 50). The main limitation comes in fact from the extragalactic source confusion itself (Dole et al. 2001).

Acknowledgements

We would like to thank A. Abergel, C. Gabriel, U. Klaas, M.-A. Miville-Deschênes and the ISOPHOT team for many interactions concerning the data reduction and the footprint analysis. We thanks Danny Dale for his help in using the template spectra for IRAS extrapolation. We thank J. L. Puget for his helpful advice all along the data reduction process.