Optimizing ISOCAM data processing using spatial redundancy

M.-A. Miville-Deschênes^1,2, F. Boulanger¹, A. Abergel¹, and J.-P. Bernard¹

1 - Institut d'Astrophysique Spatiale, Université Paris-Sud, Bât. 121, 91405 Orsay, France
2 - Département de Physique, Observatoire Astronomique du Mont Mégantic, Université Laval, Sainte-Foy, Québec, G1K 7P4, Canada

Abstract:

Several instrumental effects of the Long Wavelength channel of ISOCAM, the camera on board the Infrared Space Observatory, degrade the processed images. We present new data-processing techniques that correct these defects, taking advantage of the fact that a position in the sky has been observed by several pixels at different times. We use this redundant information (1) to correct the long-term variation of the detector response, (2) to correct memory effects after glitches and point sources, and (3) to refine the deglitching process. As an example we have applied our processing to the gamma-ray burst observation GRB 970402. Our new data-processing techniques allow the detection of faint extended emission with contrast smaller than 1% of the zodiacal background. The data reduction corrects instrumental effects to the point where the noise in the final map is dominated by the readout and the photon noises. All raster ISOCAM observations can benefit from the data processing described here. This includes mapping of solar system extended objects (comet dust trails), nearby clouds and star forming regions, images from diffuse emission in the Galactic plane and external galaxies. These techniques could also be applied to other raster type observations (e.g. ISOPHOT).

Key words: techniques: image processing -- infrared: general -- instrumentation: detectors