Parameters related to the mosaic step

The OBS1_SearchMode parameter concerns only images at a Science Window level. In the mosaic image the software always looks for K=OBS1_ToSearch sources (more significant than OBS1_MinCatSouSnr for catalog sources, or OBS1_MinNewSouSnr for the new sources), regardless the real number of sources in the field of view. Thus, if you are working with a crowded part of the sky (mainly Galactic plane and Centre) you should use a high OBS1_ToSearch number (at least 50).

There are two ways to calculate the source flux in the mosaic given the original Science Window information:

• OBS1_PixSpread = 0
  The whole input (Science Window) pixel count is put into one output (mosaic) pixel, no "spread" is done. This method optimises the flux and signal-to-noise ratio (SNR) evaluation but can sometimes give some undesired effects such as double source peaks.
• OBS1_PixSpread = 1 (default value)
  The input pixel count is spread between different output map pixels. This method is better for the source position estimate but is less accurate than the previous method for source flux estimation. SNR in the new spread mosaic will be lower than in the previous case. The source flux in this case is reduced with respect to the weighted mean of individual science windows (or mosaic obtained with OBS1_PixSpread = 0). It is not feasible to give the general estimate of this flux reduction, as it depends on image binning conditions and is different for each source position. The displacement of the center of the mosaic could be enough to change source flux. Thus, the mosaic created with OBS1_PixSpread = 1 is not suitable for flux estimation.

It is possible to decide whether you want the mosaic to be created along with the Science Window image reconstruction, or if you prefer it to be created later on. The mosaic production is controlled by the OBS1_DoPart2 parameter:

• OBS1_DoPart2 = 0
  The mosaic step is not performed and the imaging part ends after the Science Window based part.
• OBS1_DoPart2 = 1 (default value)
  The mosaic is done after the Science Window image reconstruction, in the same run.
• OBS1_DoPart2 = 2
  The mosaic is performed for images obtained from different, already existing, runs (see 9.4.1).