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LIRIS Readout Modes and Data Formats

LIRIS readout modes

  • CDS (correlated double sampling) is the standard readout mode, recommended for imaging.
  • MNDR (multiple non descructive read) can be used to reduce the readout noise, which decreases with the square root of the number of reads. This is especially useful for spectroscopy, where the background is no longer the dominating source of noise. The MNDR mode can be set with
    SYS> rmode liris mndr <Nr> <Nav>
    where <Nr> is the number of multiple reads and must be between 1 and 16. For Nr = 1 the MNDR is identical with CDS. <Nav> is the number of averaged exposures.
    For spectroscopy we recommend Nr=4.
  • The readout speed can be set to slow or fast:
    SYS> rspeed liris <speed>
  • It is possible to read only certain windows from the detector. However, we do not recommend to use this mode due to hardware limitations (see the link), and since it usually leads to confusion during data reduction.


LIRIS data formats

  • diff: The FITS file has only one extension that contains the difference between the actual exposure and the pre-read. This is the recommended read mode.
  • diff_pre: The first FITS extension contains the difference between the exposure and its pre-read, and the second one contains the pre-read only.

       SYS> storemode liris <format>

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Contact:  (LIRIS Instrument Specialist)
Last modified: 02 May 2012