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7 Conclusion

 

The data processing techniques presented here are based on the fact that each position on the sky has been observed several times and by different pixels along the observation. Taking advantage of this redundant information inherent to raster mode observations, we are able to control some instrumental effects which degrade the signal, reduce the noise level and finally bring images obtained with the LW channel of ISOCAM to a quality level close to optimal. The principal of the method presented could be generalized to all observations with spatial redundancy.

The quality of the final images is limited by our ability to separate the various instrumental effects. We have adopted a sequential approach where each of the problems is treated one after the other, but a global minimization would be a better way to find the optimal solution. However, such an approach seems to be out of reach for ISOCAM since several instrumental problems (e.g. the LTT and response variation after glitches and point sources) are presently not understood.

All raster ISOCAM observations can benefit from the data processing described here. This includes mapping of solar system extended objects (e.g. comet dust trails), nearby clouds and star forming regions, images from diffuse emission in the Galactic plane and external galaxies. Several publications based on the interpretation of ISOCAM observations reduced by the present method are being prepared.

Acknowledgements
We thank the different teams at IAS, CEA-Saclay, ENS-Paris and ESA for their outstanding work and continuous support during all phases of the ISO project. The Fond FCAR du Québec and the National Science and Engineering Research Council of Canada provided funds to support this research project. MAMD warmly thanks Leo Metcalfe for very helpful discussions and Do Kester for his judicious comments.


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