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F.5 Assessment of the Method

From the comparison of the final maps of the two GRB observations shown in Figure  F.3 we can estimate the reliability of this processing method. At first glance we see that the structure of the diffuse emission is very similar in both maps; the LTT correction applied seems to restore properly the large scale structure. Furthermore, almost all point like structures are present in both maps, giving confidence in the bad pixel identification performed. The difference of the two final sky images is shown in Figure  F.3f. It is dominated by small-scale structure noise but large-scale structures are also apparent, probably due to error in the LTT correction. Extra noise is seen at point source positions. This was expected as memory effects are not fully corrected on point sources and as we are undersampling the point spread function. One also notices that the noise level is higher at the edges of the difference map, due to less redundancy in these regions.

The noise level is reduced by a factor of ten at 8 arcmin scale and a factor of two at the resolution limit. Actually, the final maps are dominated by the readout and photon noise.


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Next: G. List of Acronyms Up: F. Optimising ISOCAM Data Previous: F.4 Bad Pixel Identification
ISO Handbook Volume II (CAM), Version 2.0, SAI/1999-057/Dc