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Glossary of Terms

channel - data channel from each 2kx2k detector through to the backend of the pipeline

pointing - a telescope slew to position with new guide star acquisition. Note that a microstep sequence is done within one pointing

read - a read is the act of physically reading a detector. This generally means the act of digitising the data, and can be either destructive (ie. followed by a clear) or non-destructive

exposure - An exposure is a sequence of one or more reads, that are used to produce a single output image

integration - An integration is a sequence of one or more exposures. Whereas the exposure is the result of a sequence of reads, the integration is a summation (or similar) of a sequence of exposures

integration sequence - An integration sequence is a sequence of integrations as the name suggests. It is characterised by the types of operations that can take place during it; an integration sequence will contain oversampling operations etc.

microstep sequence - a sequence of 1, 2x2 or 3x3 integrations taken with sub-pixel shifts.
A microstep sequence is one type of integration sequence

observation - An observation is a sequence of integration sequences that makes up a usable scientific observation. An observation is the level at which calibration frames (flats, skies, darks etc.) are collected

reduced frame - result of reducing an integration

superframe - the result from combining (interleaving) the reduced frames from a microstep sequence. Superframe is 2kx2k, 4kx4k or 6kx6k depending on microstep mode

loops - multiple exposures on one place to increase integration time

dithers - sequence of exposures or loops macrostepped in ``spiral'' pattern for use in bad pixel rejection, deep stacking etc.....

tile - any or all of four separate exposures, loops, dithers or pointings taken so as to cover a contiguous area of sky involving all 4 detectors

coadd - image resulting from combining loops taken sequentially

stack - image resulting from combining dithers including coadds if present

mosaic - complete contiguous image combined from tile exposures

confidence map - a normalised inverse variance weight map defining the ``confidence'' associated with the intensity value in each pixel, this also encodes for hot pixels, bad pixels, dead pixels and so on. The raw confidence maps for each frame output by the Data Acquisition System (DAS) will be derived from regular (frequency TBD) analysis of the calibration flats and darks. All output processed frames (stacked, tiled, mosaiced etc.) will also have an associated derived confidence map.

next up previous
Next: General Issues Up: APPENDICES Previous: APPENDICES
Nigel Hambly 2002-10-02