Data Reduction Terminology

Background The contribution to the counts in a pixel from the dark current and the thermal background of the instrument.
Dark current Electrons introduced into the pixel from sources other than photons
Final read the last read of an observation
Loop In NDR mode, during an integration the detector may be sampled a number of times with a delay between sucessive samples. The number of loops is the number of samples that have a time delay between them. i.e. in 4 Loop, 2 Read mode, the chip is read out twice at the start of the integration, this is loop 1 reads 1 and 2. The chip is then allowed to integrate, and is then read out again twice. This is loop 2, reads 1 and 2, following another delaly, loop 3 reads 1 and 2 and a final dealy before loop 4 reads 1 and 2. Thus loops have integration time between them, reads do not.
NDR Non Destructive Read. Unlike with CCD's the act of measuring and recording the signal from the pixels does not reset the pixels. Thus it is possible to read out the array a number of times during an integration and effectively watch the pixels integrate. This is non destructive readout mode.
Observation A reset, followed by a set of loops and reads at one position
PixCel PixCel is the software package which controls the CCD. PixCel will mosaic the four quadrants together, and will output one FITS file for every read.
Read The act of measuring and recording the output voltages from each of the pixels on the chip, to produce one data frame. If this is done repeatedly, producing a series of data frames with no time delay between them, then this would be a number of successive reads.
Reset Apply a defined voltage VRESET to every pixel on the detector to remove accumulated counts and initialise the device.
Sky Photons from the sky
Thermal background Detected photons that are produced by the Black Body emission from the Instrument.
Zeroth read The read containing the bias level for each pixel. (Currently loop1 read 2.)

Andrew J. Dean. <>
Last modified: Thu Feb 10 15:49:12 2000