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3.6 Sparse Maps

A special mode of mapping was sparse mapping. This was a sequence of irregularly spaced positions within an area of 3 degrees in diameter, with the first selected pointing determining the centre. Contrary to the normal mapping modes, multi-filter observations were carried out such that the complete set of requested filters was measured at each position before moving to the next position. This mode facilitated observations of a cluster of sources in a small area. As the detector remained switched-on all the time the signal stability was increased and the times for overheads were reduced. Additionally, the dynamic range of the detector was adjustable to the brightness at each individual position. It was recommended to perform the sequence such, that the total intensity increased in order to avoid strong, long lasting signal transients which usually occured when moving from a very bright spot to a faint patch.

ISO Handbook Volume IV (PHT), Version 2.0.1, SAI/1999-069/Dc