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: http://www.stsci.edu/instrument-news/handbooks/nicmos/c12_pipeline.doc2.html
Дата изменения: Thu Aug 7 20:42:46 1997 Дата индексирования: Tue Feb 5 12:26:38 2013 Кодировка: Поисковые слова: arp 220 |
The basic sequence of steps in the STScI pipeline system (also known as OPUS) is:
The calibration step has several goals:
An illustrative (partial) counter example to this procedure is the WFPC2 CRSPLIT proposal instruction. This results in two WFPC2 exposures from a single line on the exposure logsheet (the way in which observers specify commands for HST). However, the HST ground system treats a CRSPLIT as two distinct exposures which are commanded, processed, calibrated, and archived separately. The pipeline does not combine these two images (datasets) to create the single image without cosmic ray events which was the observer's original intention. Presently, the observers (and any future archival researchers) are left to perform this task on their own.
The second generation instruments present many instances in which the combination of data from two or more exposures is necessary to create a scientifically useful data product. Both NICMOS and STIS will need to combine exposures to remove cosmic rays and to improve flat fielding (by dithering or stepping). For NICMOS, the HST thermal background is expected to have significant temporal variations. Multiple exposures (dithered for small targets and offset onto blank sky-chopped-for larger targets) will be necessary to measure and remove this background. While this has been standard practice for ground based infrared observations and is the basis of essentially all existing infrared data reduction schemes, it is a new paradigm for the HST ground system.
An association is a set of one or more exposures along with an association table and, optionally, one or more products. We define the following terms:
From a high level, an association is a means of identifying a set of exposures as belonging together and being, in some sense, dependent upon one another. The association concept permits these exposures to be calibrated, archived, retrieved, and reprocessed (within OPUS or STSDAS) as a set rather than as individual objects. In one sense, this is a book-keeping operation which is being transferred from the observer to the HST data pipeline and archive.
Associations are defined by optional parameters on a single exposure logsheet line. That is, there is a one-to-one correspondence between proposal logsheet lines and associations (although it is possible to have exposures which are not in associations).
Observers may obtain one or more exposures at each of one or more positions on the sky using the NICMOS proposal grammar. Typically usage will be: