The VISIR Upgrade Project

Introduction

VISIR, the mid-infrared imager and spectrograph on the Very Large Telescope has now been successfully in operation for more than five years. Since the introduction of VISIR, mid-infrared detector technology has advanced significantly, and ESO, in collaboration with members of the consortium that built VISIR (CEA Saclay, France and ASTRON, the Netherlands) is currently launching a project to upgrade VISIR and its capabilities. A new detector will be the most prominent upgrade to the hardware providing better sensitivity, stability and overcoming the electronic artifacts. Based on feedback from the user community, it was decided that several other measures to optimize hardware, software and operations will also be implemented as part of the VISIR Upgrade Project.

Scope

The main part of the VISIR upgrade project will be the upgrade of the DRS (former Boeing) 256x256 BIB detector to a Raytheon 1024x1024 pixel Aquarius array. The new detector will offer a larger field-of-view (for imaging), and extended recorded spectral range (for spectroscopy), better cosmetics, and -- especially for spectroscopy -- improved sensitivity. In addition to this main part of the upgrade, several other new features will be implemented:

  • During the upgrade project, a prism will be installed in VISIR that will enable the entire N-band (8-12 μm) spectrum to be recorded in a single exposure in low-resolution (R = 200) spectroscopy mode. This new low-resolution prism mode is envisioned to largely replace VISIR's current low-resolution grism spectroscopy mode, which needs four different exposures to cover an equivalent wavelength range. This new observing mode will be offered in both visitor- and service-mode.

  • The stability of the images delivered by VISIR will be improved. We are working toward offering diffraction-limited image quality in the N- and Q-bands under median seeing conditions on Paranal with the post-upgrade VISIR.

  • New coronagraphic and sparse aperture masking (SAM) modes will be implemented in the course of the VISIR upgrade project. It is expected that initially these modes would be offered for visitor-mode observations only.

  • Precipitable Water Vapour (PWV) is the main source of opacity at mid-infrared wavelengths. Furthermore, the PWV contents of the atmosphere is highly variable. To be able to better match the scientific needs of each programme to the ambient conditions, ESO is installing a PWV monitor on Paranal as part of the VISIR upgrade project. PWV is anticipated to become a user-defined constraint for VISIR service-mode observations starting with ESO period 90.

  • The VISIR data-reduction pipeline will be upgraded to support the new detector and the new observing modes. In addition, several existing shortcomings will be remedied.

Schedule

The VISIR Upgrade Project has successfully passed it Preliminary Design Review (PDR) and Final Design Review (FDR) in September 2010 and July 2011, respectively. VISIR will be unavailable for science observations during the implementation phase of the upgrade project (June 2012-Early 2014). The post-upgrade VISIR is currently expected to be offered back to the user community for regular science observations starting in ESO period 93 (from April 2014 onwards). Further news about the upgrade project will be listed in the News section of this web-page.

News

  • June 2011
  • October 2011
  • December 2011
    • The Precipitable Water Vapour (PWV) monitor has been installed and successfully commissioned on Paranal! Initial estimates of the performance of the PWV monitor show that it meets all specifications:

  • PWV range 0.5-9 mm validated
  • PWV precision: ca 30 μm
  • PWV accuracy: ca 0.1 mm
  • High time resolution (sec)
  • All sky pointing, 2D capability
  • Autonomous operation


    • The new Water Vapour Radiometer with the commissioning team in front of VLT UT4 (Yepun).


    Comparison of Water Vapour Radiometer measurements (blue dots) with in-situ water-vapour measurements from radiosonde launches attached to weather balloons (black diamonds) and values derived from various other instruments.

  • May 2012
  • June 2012
    • First light has been achieved (in the integration hall) with the new Aquarius detectors assembled within VISIR!




  • July 2012
    • VISIR has been successfully re-assembled, and has been mounted back on VLT UT3 (Melipal). Re-commissioning of the upgraded VISIR will start on July 28th.

    The re-commissioning team:

    July 29: First light on-sky has been achieved with VISIR 2.0 in imaging mode!

  • August 2012
    • August 1: First light on-sky has been achieved with the new low-resolution prism mode!

    August 12: The first VISIR re-commissioning run has ended. The optical quality of the new VISIR is superb, and all modifications including the new prism based low resolution spectroscopy work well. Offline and on-sky tests of the new modes (various flavours of coronagraphy and SAM-imaging) are very encouraging.

    However, VISIR is not yet ready for science operations. During the first re-commissioning run there were performance problems of the new Aquarius arrays read-out by the new NGC detector controller. In its present state the instrument does not meet the sensitivity expectations.

    VISIR will therefore be dis-mounted from VLT UT3 (Melipal) before the end of August 2012, for further testing. If deemed necessary, the imaging detector may be exchanged before re-mounting VISIR back on the telescope in early September. At present, we expect further re-commissioning activities of VISIR to take place in the bright time period in October.

  • October 2012
    • Further testing has confirmed that VISIR's sensitivity after the upgrade is out of specification. Therefore the instrument has been taken off the telescope and various issues are still being worked on in order to properly diagnose the problem and quantitatively characterize the performance parameters. The situation is being analyzed and a short term as well as a long term recovery plan are being drafted. Until the instrument behaviour is fully understood and characterized, VISIR will not be available for operations. This situation is expected to last for the remainder of ESO period 90 (until the end of March 2013). Therefore all VISIR observing runs for ESO period 90 have been canceled.
  • December 2012
    • Work on the VISIR recovery plan is on-going. In collaboration with the manufacturer, ways to mitigate the effects on the final sensitivity of the behaviour of the new detectors in the high-background regime (for imaging) are being studied. In addition, the detector for the spectroscopic arm will be exchanged. No observing time on VISIR will be allocated until the instrument has successfully been re-commissioned. Therefore no VISIR proposals are accepted for ESO periods 91 and 92.