The VISIR Upgrade Project
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.
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
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
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.
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.
- October 2011
A 183 GHz Precipitable Water Vapour (PWV) monitor has been delivered
to ESO by its manufacturer, Radiometer Physics GMBH of Meckenheim, Germany, and has successfully passed Preliminary
Acceptance Europe (PAE) after being tested at the UFS Schneefernerhaus (2650 m, below Zugspitze) in the Alps.
View of the UFS Schneefernerhaus.
The new Water Vapour Radiometer on the terrace of the UFS Schneefernerhaus.
- 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
- 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
The hardware upgrade of VISIR has started! After passing the shipment readiness review, the new detectors and other components of the hardware upgrade have been shipped to Paranal! The last set of observations on-sky obtained with VISIR in its old state was a set of close-out calibrations (a special set of measurements designed to get a quantitative estimate of the instrument performance before the upgrade) on the standard star HD 178345 on May 9, 2012. Subsequently, VISIR was taken off the telescope and taken to the integration hall where the new hardware will be integrated into the instrument.
The empty VISIR cryostat (instrument disassembled)
- 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
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.