Arizona State University College of Liberal Arts and Sciences


AR 11258 — STIS/CCD Side-2 pattern noise removal
Apr 28 2015 — This web site was off-line the past weeks due to a server hardware failure. We regret any inconvenience this may have caused.
May 30 2014 — This web site will be offline for several hours starting 2 PM (MST = UT - 7h) for physical relocation to a different room and maintenance.

When STIS resumed operations in July 2001 using the redundant "Side-2" electronics, the read-noise of the CCD detector appeared to have increased by ~1 e due to a superimposed and highly variable "herring-bone" pattern noise. For many programs that aim to detect signals near the STIS design limits, the impact of this noise is far more serious than implied by a mere 1 e increase in the amplitude of the read-noise, as it is of a systematic nature. Peak-to-valley deviations on spatial scales of only a few pixels can be as large as ~8 e.

    
Example — [left] A portion of a raw, gain=4 BIAS frame o6hn4x020, taken in 2002 February; [middle] the pattern-free cleaned version available here; [right] move your cursor over the image to blink between the original and pattern-free frames. The pattern noise is even more apparent in gain=1 frames.

We perfected a method to cleanly and robustly detect and remove this pattern-noise from raw STIS CCD frames (Jansen, Collins & Windhorst 2002). After removal of the pattern noise, we successfully reproduce the nominal "Side-1" CCD read-noise as observed prior to 2001 July. As part of an approved Cycle 16 Archival Calibration Legacy program (AR 11258; PI: Rolf Jansen) we removed the pattern noise from all 75345 raw, un-binned, full-frame "Side-2" STIS/CCD frames (47192 datasets) taken between 2001 July and the short that rendered STIS inoperable early in 2004 August. A more detailed paper describing the method, the nature of the noise, and trends therein over time is Jansen et al. 2010 (in: 'The 2010 STScI Calibration Workshop', Eds. S. Deustua & C. Oliveira, [STScI; Baltimore], pp.449–455 ).

In Fall 2012, Jansen also removed the pattern noise from all 30584 raw, un-binned, full-frame "Side-2" STIS/CCD frames (12958 datasets) taken between 2009 June 2 and 2011 October 31, i.e., presently public data taken after the repair of STIS during the final HST Servicing Mission (Jansen 2013, AAS#221 [344.11]).

Unbinned subframe-readout "Side-2" STIS/CCD data, i.e., with 1060×N for even N ≥ 16 pixels, is now also supported. For the smaller (≤ 256 pixel) formats, one should expect only partial removal of the pattern noise (since there is much less information in the frequency power spectrum). Nonetheless, a marked improvement over uncorrected data was demonstrated.

Through this web-portal, users may search for and download pattern-free datasets of interest (or, alternatively, pattern-only datasets) via a series of index pages. In the future, we may support requests of all data for a given observing program (Proposal ID) at once.


July 2001 – August 2004 June 2009 – October 2011
Search by Proposal ID Search by Principal Investigator Search by Proposal ID Search by Principal Investigator
Search by Target Name Search by Date of Observation Search by Target Name Search by Date of Observation
Search by Right Ascension Search by Exposure Time Search by Right Ascension Search by Exposure Time

Pattern-free bias calibration reference images Pattern-free bias calibration reference images
Pattern-free dark calibration reference images Pattern-free dark calibration reference images

Documentation and Software (written and tested on machines running Redhat-like Linux)

Past/present team members: Rolf Jansen (PI; ASU), Rogier Windhorst (ASU), Hwihyun Kim (ASU), Nimish Hathi (UCR,OCIS), Paul Goudfrooij (STScI), & Nick Collins (CUA/IACS,GSFC). Most of this work was funded by grants HST-AR-11258 and HST-GO-9066 from STScI, which is operated by AURA under NASA contract NAS5-26555.



    
Example 2 — [left] A portion of a raw, gain=1 image (o6g354010) of Herbig-Haro object HH 30, taken in 2003 January; [middle] the pattern-free cleaned version available here; [right] move your cursor over the image to blink between the original and pattern-free frames.


In case of problems with this page, contact: Rolf.Jansen @ asu.edu , tel.: (480)727-7119
Last updated: Apr 28, 2015

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