Basic Data Modes: STARE and NDSTARE
ALICE (Array Limited Infrared Control Environment) is a transputer-based computer and electronics system which controls the IRCAM/TUFTI array configuration, the exposure and readout of the array, and pre-processes the imaging data before transmission to the host computer. Multiple, coadded, images have their data counts divided by the number of coadds before the single frame is stored to disk.
In STARE mode the array is reset and read after the user-defined on-chip exposure times. With NDSTARE the array is reset, read immediately, and read again after the user-defined on-chip exposure time. The difference between the post-exposure and pre-exposure images is taken and stored. Hence NDSTARE removes the bias level of about 25000 counts, also use of NDSTARE reduces the read noise from about 56 electrons to about 40 electrons. However the extra overhead of the additional read makes NDSTARE inappropriate for exposures shorter than about 1 second – it is not efficient, and moreover many short NDSTARE exposures can lead to BDS errors.
Minimum exposures times are set by the number of pixels being read out and by the readout mode. IRCAM/TUFTI has “Standard” and “Fast” readout modes available; “Standard” should be used if possible as “Fast” results in noisier data (to avoid saturation change the array bias level and use “Deepwell” in preference to “Fast” readout, see the linearity discussion in the next section). The overhead in reading out is equal to the minimum exposure time.