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Dark Energyand
Large Synoptic Survey Telescope
Precision Calibration Apparatus:Calibrating the Throughput and Response of
Astronomical Instrumentation
Department of Energy Site VisitAugust 21, 2009
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
Peter DohertyHarvard University Laboratory for Particle Physics and Cosmology
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
2DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Precision Calibration: Introduction
We improve upon traditional celestial calibration sources by:• Measuring a source with a known spectrum, namely, a narrowband
tunable laser• Compare the system response (telescope throughput) to a known
detector (NIST-calibrated photodiode)• In a related (but separate) effort, continuously monitoring the
atmosphere during acquisition of astronomical data
Measurement of a source is a sum of integrals:
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
3DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Current and Future Efforts:
Calibrating the Telescope and Detector:
• Pan-STARRS Calibration Screen
• LSST Calibration Screen
• Portable Calibration System
Monitoring Atmospheric Throughput:
• Real time water vapor monitor system (Leibler)
• Tunable-Lidar monitoring of atmospheric extinction (with UNM/GTRI)
Precision Calibration: Current and Future
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
4DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Precision Calibration: Calibration Procedure
Wavelength Calibration Procedure
• Illuminate full telescope aperture with monochromatic light• Take a calibration “flat” while monitoring input light with calibrated
photodiode• Normalize flat to flux seen by photodiode• Move to the next wavelength and repeat, until entire visible
spectrum is spanned• Construct wavelength-dependent response for each pixel in the
telescope’s CCD camera
• End result: Measurement of relative system throughput, including telescope mirrors, corrector optics, filters, and detector
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
5DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Pan-STARRS Calibration Screen: Overview
Accomplished:Installation of the world’s most advanced telescope instrument calibration system in the Pan-STARRS dome at Haleakala Hawaii
Features:
Rear projection screen mounted inside telescope dome
Multiple fixed and tunable light sources:Quartz tungsten halogen white lightNIST SIRCUS Laser (680 to 1100 nm)Supercontinuumlaser and monochromator (450 to 1100 nm)
NIST calibrated photodiode for flux calibration
Digital Micro-mirror Device for image projection
Integrated into telescope control system
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
6DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Pan-STARRS Calibration Screen: Diagram
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
7DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Pan-STARRS Calibration Screen: Assembly
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
8DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Pan-STARRS Calibration Screen: Photograph
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
9DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Pan-STARRS Calibration Screen: Installed
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
10DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
System Enhancements 2009/2010:
Installation of Ekspla Tunable laser for wavelength coverage from 350 nm to 1100 nm with a single source
Improved Photodiode measurement and control system for more precise flux measurements
Closing the loop with the CCD/DMD image flattener
Further integration of instrument into telescope system software
Incorporating calibration data into the Pan-STARRS Image Processing Pipeline
Pan-STARRS Calibration Screen: Future Plans
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
11DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
LSST Calibration Screen: Overview
Similar in concept to Pan-STARRS calibration screen,but much different in scale:
Similarities:
Ekspla (or similar) tunable laser source withwavelength coverage from 350 nm to 1100 nm
NIST calibrated photodiode(s) for flux measurements
Differences:
Cannot use single DMD projector: not enough focallength, and a large central obscuration
Much larger!Pan-STARRS = 1.8 meters, LSST = 8.5 meters
Multiple small projectors?
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
12DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Comparison of Pan-STARRS Mirror Size to LSST Mirror Size
LSST Calibration Screen: LSST vs. Pan-STARRS
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
13DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Filling the LSST Aperture with “Small” Projectors
LSST Calibration Screen: Filling the Aperture
12 Projectors - 1.7m Diameter 48 Projectors - 0.85m Diameter
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
14DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
LSST Calibration Screen: Small Projector
Concept: A fiber fed parabolic reflector
Parabolic Mirror
Optical Fiber
Diffuse emitter and parabolic collimator. Light from a fiber is collimated and illuminatesa diffuser. The size of the diffuse emitter determines the range of angles into which lightis emitted. Uniform surface brightness on the emitter ensures uniform intensity into all angles.
Diffuser
Lens
LPPC is currently constructing a prototype in our optics lab
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
15DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
LSST Calibration Screen: “Leaky” Fiber Panel
Concept: A flat screen built of glowing optical fiber
Optical Fiber
Mirror
Collimator
Diffuser
A prototype screen assembled in LPPC LabWould a spiral work better?
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
16DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Portable Calibration System: Overview
A transportable light source and photon flux measurement system for calibrating throughput of astronomical telescopes and instrumentation
Makes use of existing observatory dome screen
Flexible I/O and triggering modes to support a wide variety of operating modes allowing integration with diverse telescope systems
In 2009/2010 LPPC will design and construct the Integrating Photodiode Amplifier. Other parts are COTS.
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
17DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Atmospheric Water Vapor: Overview
Variation in aerosols and water vapor are the main sources of temporal variation in atmospheric transmission, and the airmass dependence of extinction varies with wavelength.
To investigate these two effects (aerosols and water vapor) we are engaged in two lines of research:
1.Monitoring water vapor in the atmosphere via differential imaging
2.Measuring atmospheric aerosol content via lidar backscatter
We are engaged in experiments of both types.
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
18DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Calibration: Undergraduate Projects
Atmospheric Water Vapor via Differential Imaging
Concept: Monitor bright stars simultaneously in two pass-bands:940nm (on absorption line) and 880nm (off absorption line).
1.Monitor cloud density and correlate with simultaneous imaging through the CTIO 4m Blanco telescope
2.Distribution of water vapor and its variability spatially andtemporally as well as airmass dependence.
Two undergraduates travelled to CTIO in Chile with Dr. Stubbs inearly July and are working to reduce their data and determine the results.
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
19DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Monitoring Atmospheric Extinction
“Light from distant galaxies travels towards Earth-based telescopes for millions of years, and in the last millisecond of its trip about 20 percent of that valuable light, which carries information about the very structure of the universe, is lost as it traverses our atmosphere. For centuries, astronomers have looked through the atmosphere with their telescopes, but have seldom looked at the atmosphere in an effort to precisely correct for this lost light.”
-John McGraw, Professor of Physics and Astronomy, University of New Mexico
UNM/GTRI Astronomical Lidar for Extinction (ALE)
ALE has been developed by the University of New Mexico and the Georgia Institute of Technology Research Institute
Measures backscatter from the stratosphere to monitor minute-to-minute changes in extinction due to aerosols
Current system uses a fixed, 537 nm source
Harvard/LPPC will collaborate with ALE creators in testing the system using a tunable laser source with wavelength coverage from 410 to >1100 nm
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
20DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty
Precision Calibration Apparatus: Credits
Harvard University/LPPC:Christopher Stubbs, Professor of Physics and AstronomyPeter Doherty, Senior Instrumentation EngineerSteve Sansone, Scientific Instrument BuilderGautham Narayan, Graduate StudentClaire Cramer, Post-Doctoral Research ScientistCamille Leibler, Undergraduate StudentKenneth Gottlieb, Undergraduate Student
National Institute of Standards and TechnologyKeith Lykke, Physicist, Laser Applications GroupSteven Brown, Physicist, Laser Applications GroupJohn Woodward, Physicist, Laser Applications GroupAllan Smith, Physicist, Laser Applications Group
University of Hawaii, Institute for AstronomyJohn Tonry, Astronomer Jeffrey Morgan, Pan-STARRS Sr. Telescope Supervising Engineer Robert Calder, PS1 Operations Manager
Large Synoptic Survey TelescopeKirk Gilmore, LSST Camera System Scientist, SLACDavid L. Burke, Kavli Institute for Particle Astrophysics and Cosmology, SLAC
Laser Applications Group