The Dark Energy Survey (DES) is an operating optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES has completed its third observing season out of a nominal five. This paper describes DES “Year 1” (Y1) to “Year 3” (Y3), the strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of the first three season's data, and describes how we are adjusting the survey strategy in the face of the El Niño Southern Oscillation.
The Dark Energy Survey (DES) is a next generation optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES started its first observing season on August 31, 2013 and observed for 105 nights through mid-February 2014. This paper describes DES “Year 1” (Y1), the strategy and goals for the first year's data, provides an outline of the operations procedures, lists the efficiency of survey operations and the causes of lost observing time, provides details about the quality of the first year's data, and hints at the “Year 2” plan and outlook.
The Dark Energy Camera (DECam) is a new 520 Mega Pixel CCD camera with a 3 square degree field of view built for
the Dark Energy Survey (DES). DECam is mounted at the prime focus of the Blanco 4-m telescope at the Cerro-Tololo
International Observatory (CTIO). DES is a 5-year, high precision, multi-bandpass, photometric survey of 5000 square
degrees of the southern sky that started August 2013. In this paper we briefly review SISPI, the data acquisition and
control system of the Dark Energy Camera and follow with a discussion of our experience with the system and the
lessons learned after one year of survey operations.
Scientific CCD detectors are typically readout using the Correlated Double Sampling (CDS) technique. At low
pixel rates, noise of ~2e- RMS is typically achieved. The limitation for reaching lower noise comes from the 1/f
component on the output of the CCD, and this noise cannot be eliminated using CDS. A new readout technique
based on a digital filter is presented here for suppressing the 1/f. Using this new technique a noise of 0.4e- is
The Dark Energy Survey Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square
degree, 570 Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be
used to perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. All components of
DECam have been shipped to Chile and post-shipping checkout finished in Jan. 2012. Installation is in progress. A
summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and
commissioning will be presented.
The Dark Energy Survey CCD imager was constructed at the Fermi National Accelerator Laboratory and delivered to
the Cerro Tololo Inter-American Observatory in Chile for installation onto the Blanco 4m telescope. Several efforts are
described relating to preparation of the instrument for transport, development and testing of a shipping crate designed to
minimize transportation loads transmitted to the camera, and inspection of the imager upon arrival at the observatory.
Transportation loads were monitored and are described. For installation of the imager at the telescope prime focus,
where it mates with its previously-installed optical corrector, specialized tooling was developed to safely lift, support,
and position the vessel. The installation and removal processes were tested on the Telescope Simulator mockup at
FNAL, thus minimizing technical and schedule risk for the work performed at CTIO. Final installation of the imager is
scheduled for August 2012.
We describe the preliminary design of the Dark Energy Spectrometer (DESpec), a fiber-fed spectroscopic instrument
concept for the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (CTIO). DESpec would take
advantage of the infrastructure recently deployed for the Dark Energy Camera (DECam). DESpec would be mounted in
the new DECam prime focus cage, would be interchangeable with DECam, would share the DECam optical corrector,
and would feature a focal plane with ~4000 robotically positioned optical fibers feeding multiple high-throughput
spectrometers. The instrument would have a field of view of 3.8 square degrees, a wavelength range of approximately
500<<1000 nm, and a spectral resolution of R~3000. DESpec would provide a powerful spectroscopic follow-up
system for sources in the Southern hemisphere discovered by the Dark Energy Survey and LSST.λ
The Dark Energy Camera and its cooling system has been shipped to Cerro Tololo Inter-American Observatory in Chile
for installation onto the Blanco 4m telescope. Along with the camera, the cooling system has been installed in the Coudé
room at the Blanco Telescope. Final installation of the cooling system and operations on the telescope is planned for the
middle of 2012. Initial commissioning experiences and cooling system performance is described.
The Dark Energy Camera (DECam) is the new wide field prime-focus imager for the Blanco 4m telescope at CTIO.
This instrument is a 2.2 sq. deg. camera with a 45 cm diameter focal plane consisting of 62 2k × 4k CCDs and 12 2k × 2k
CCDs and was developed for the Dark Energy Survey that will start operations at CTIO in 2011. DECam includes the
vessel shell, the optical window cell, the CCDs with their readout electronics and vacuum interface, the focal plane
support plate and its mounts, and the cooling system and thermal controls. Assembly of the imager, alignment of the
focal plane and installation of the CCDs are described. During DECam development a full scale prototype was used for
multi-CCD readout tests. This test vessel went through several stages as the CCDs and related hardware progressed
from early prototypes to final production designs.
The Dark Energy Camera (DECam) is the new wide field prime-focus imager for the Blanco 4m telescope at CTIO. This
instrument is a 3 sq. deg. camera with a 45 cm diameter focal plane consisting of 62 2k × 4k CCDs and 12 2k × 2k CCDs
and was developed for the Dark Energy Survey that will start operations at CTIO in 2011. The DECam CCD array is
inside the imager vessel. The focal plate is cooled using a closed loop liquid nitrogen system. As part of the development
of the mechanical and cooling design, a full scale prototype imager vessel has been constructed and is now being used
for Multi-CCD readout tests. The cryogenic cooling system and thermal controls are described along with cooling
results from the prototype camera. The cooling system layout on the Blanco telescope in Chile is described.
The Dark Energy Survey Camera (DECam) will be comprised of a mosaic of 74 charge-coupled devices (CCDs). The
Dark Energy Survey (DES) science goals set stringent technical requirements for the CCDs. The CCDs are provided by
LBNL with valuable cold probe data at 233 K, providing an indication of which CCDs are more likely to pass. After
comprehensive testing at 173 K, about half of these qualify as science grade. Testing this large number of CCDs to
determine which best meet the DES requirements is a very time-consuming task. We have developed a multistage
testing program to automatically collect and analyze CCD test data. The test results are reviewed to select those CCDs
that best meet the technical specifications for charge transfer efficiency, linearity, full well capacity, quantum efficiency,
noise, dark current, cross talk, diffusion, and cosmetics.
Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely
red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty
two 4k2k and twelve 2k2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and
a eld of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will
cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from
To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down
for the design of DECam. Among them, the
atness of the focal plane needs to be controlled within a 60-micron
envelope in order to achieve the specied PSF variation limit. It is very challenging to measure the
the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image
based techniques to measure the
atness of the focal plane. By imaging a regular grid of dots on the focal plane,
the CCD oset along the optical axis is converted to the variation the grid spacings at dierent positions on the
focal plane. After extracting the patterns and comparing the change in spacings, we can measure the
to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal
plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the
pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by dierent
CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are
in good agreement with the direct optical measurements.
The Dark Energy Camera is a new prime-focus instrument to be delivered to the Blanco 4-meter telescope at the Cerro
Tololo Inter-American Observatory (CTIO) in 2011. Construction is in-progress at this time at Fermilab. In order to
verify that the camera meets technical specifications for the Dark Energy Survey and to reduce the time required to
commission the instrument while it is on the telescope, we are constructing a "Telescope Simulator" and performing full
system testing prior to shipping to CTIO. This presentation will describe the Telescope Simulator and how we use it to
verify some of the technical specifications.
We have developed a design for packaging Charged Coupled Devices (CCDs) for use as optical imaging devices for
space applications, although the design is also useful for any large ground-based mosaic. We have constructed and
assembled prototype packages using this design. Testing of these prototypes has demonstrated that these packaged
CCDs are flight worthy. The design, construction, and testing of these prototypes are described in this article.
The Dark Energy Camera is an wide field imager currently
under construction for the Dark Energy Survey.
This instrument will use fully depleted 250 μm thick
CCD detectors selected for their higher quantum efficiency
in the near infrared with respect to thinner devices.
The detectors were developed by LBNL using
high resistivity Si substrate. The full set of scientific
detectors needed for DECam has now been fabricated,
packaged and tested. We present here the results of
the testing and characterization for these devices and
compare these results with the technical requirements
for the Dark Energy Survey.
The Dark Energy Survey Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 520
Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to
perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. Construction of
DECam is well underway. Integration and testing of the major system components has already begun at Fermilab and
the collaborating institutions.
Fully depleted, back-illuminated, p-channel CCDs developed at Lawrence Berkeley National Laboratory exhibit high
quantum efficiency in the near-infrared (700-1050nm), low fringing effects, low lateral charge diffusion (and hence
small, well-controlled point spread function), and high radiation tolerance. Building on previous efforts, we have
developed techniques and hardware that have produced space-qualified 4-side abuttable, high-precision detector
packages for 10.5μm pixel, 3.5k x 3.5k p-channel LBNL CCDs. These packages are built around a silicon carbide
mounting pedestal, providing excellent rigidity, thermal stability, and heat transfer. Precision fixturing produces
packages with detector surface flatness better than 10μm P-V. These packages with active areas of 36.8mm square may
be packed on a detector pitch as small as 44mm. LBNL-developed Front End Electronics (FEE) packages can mount
directly to the detector packages within the same footprint and detector pitch. This combination, along with identically
interfaced NIR detector/FEE packages offers excellent opportunities for high density, high pixel count focal planes for
space-based, ground-based, and airborne astronomy.
DECam is a 520 Mpix, 3 square-deg FOV imager being built for the Blanco 4m Telescope at CTIO. This facility
instrument will be used for the "Dark Energy Survey" of the southern galactic cap. DECam has chosen 250 μm thick
CCDs, developed at LBNL, with good QE in the near IR for the focal plane. In this work we present the characterization
of these detectors done by the DES team, and compare it to the DECam technical requirements. The results demonstrate
that the detectors satisfy the needs for instrument.
The Dark Energy Survey is planning to use a 3 sq. deg. camera that houses a ~ 0.5m diameter focal plane of 62 2k×4k
CCDs. The camera vessel including the optical window cell, focal plate, focal plate mounts, cooling system and thermal
controls is described. As part of the development of the mechanical and cooling design, a full scale prototype camera
vessel has been constructed and is now being used for multi-CCD readout tests. Results from this prototype camera are
DECam, camera for the Dark Energy Survey (DES), is undergoing general design and component testing.
For an overview see DePoy, et al in these proceedings. For a description of the imager, see Cease, et al in
these proceedings. The CCD instrument will be mounted at the prime focus of the CTIO Blanco 4m
telescope. The instrument temperature will be 173K with a heat load of 113W. In similar applications,
cooling CCD instruments at the prime focus has been accomplished by three general methods. Liquid
nitrogen reservoirs have been constructed to operate in any orientation, pulse tube cryocoolers have been used
when tilt angles are limited and Joule-Thompson or Stirling cryocoolers have been used with smaller heat
loads. Gifford-MacMahon cooling has been used at the Cassegrain but not at the prime focus. For DES, the
combined requirements of high heat load, temperature stability, low vibration, operation in any orientation,
liquid nitrogen cost and limited space available led to the design of a pumped, closed loop, circulating
nitrogen system. At zenith the instrument will be twelve meters above the pump/cryocooler station. This
cooling system expected to have a 10,000 hour maintenance interval. This paper will describe the
engineering basis including the thermal model, unbalanced forces, cooldown time, the single and two-phase
We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey.
DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo
International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector,
five filters (g,r,i,z,Y), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of
62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of
view. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley
National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms,
and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.
A description of the plans and infrastructure developed for CCD testing and characterization for the DES focal plane detectors is presented. Examples of the results obtained are shown and discussed in the context of the device requirements for the survey instrument.
The Dark Energy Survey Camera focal plane array will consist of 62 2k x 4k CCDs with a pixel size of 15 microns and
a silicon thickness of 250 microns for use at wavelengths between 400 and 1000 nm. Bare CCD die will be received
from the Lawrence Berkeley National Laboratory (LBNL). At the Fermi National Accelerator Laboratory, the bare die
will be packaged into a custom back-side-illuminated module design. Cold probe data from LBNL will be used to
select the CCDs to be packaged. The module design utilizes an aluminum nitride readout board and spacer and an Invar
foot. A module flatness of 3 microns over small (1 sqcm) areas and less than 10 microns over neighboring areas on a
CCD are required for uniform images over the focal plane. A confocal chromatic inspection system is being developed
to precisely measure flatness over a grid up to 300 x 300 mm. This system will be utilized to inspect not only room-temperature
modules, but also cold individual modules and partial arrays through flat dewar windows.
A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Iz supernovae and to standardize the magnitude of each candidate by determining explosion parameters. The spectrograph is also a key element for the calibration of the science mission. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have high efficiency and low spectral resolution (R~100), constant through the wavelength range (0.35-1.7μm), adapted to the scientific goals of the mission.