The Solar Radiation and Climate Experiment (SORCE) recorded daily Solar Spectral Irradiance (SSI) measurements from 2003 to 2020, overlapping with the Total and Spectral Irradiance Sensor (TSIS1) for ∼2 years (Mar. 2018 - Feb. 2020). We use data from the Spectral Irradiance Monitors (SIM), spanning 704 days and 554 time-matched observations, to compare absolute irradiance calibrations in a truly unique space-based UV-IR spectroscopic overlap study. This 200–2400 nm comparison was conducted during the Solar Cycle 24 minimum, so observed differences are likely instrumental. We find peak-to-peak (maximum) absolute scale differences of 12% with a mean fractional difference of 0.7 ± 2.9%. A multiplicative scale correction factor (STICR) has been developed to reconcile the TSIS1 and SORCE SIM irradiance differences. Applying this correction to the SORCE-SIM V27 dataset, we provide a re-calibrated dataset known as the TSIS1-SIM Adjusted Values (TAV). We discuss the challenges in the creation of STICR and TAV, and lessons learned about using temporally overlapping space observatories to provide a continuous solar observation record.
Solar observations are intrinsically harsh to optics and detectors. Space measurements in particular expose the spacecraft and payload to charged particles and UV radiation which causes changes in the transmission profile of windows and optics. These affect the absolute accuracy of the measurements over time. Astronomical observations typically rely on standard stars and calibration sources to track and correct changes in the instrument. This method was used with the SORCESOLSTICE instrument during its 17 year Solar Spectral Irradiance (SSI) measurement record covering more than 9 orders of magnitudes in brightness between stellar and Solar observations. Other instruments are designed with multiple identical channels which are used at various cadence to track degradation differentially. We present the advantages and issues discovered with each method and the benefits of following a constant and regular observation plan to improve the accuracy of the degradation corrections.
The Solar Radiation and Climate Experiment (SORCE) is a NASA-sponsored satellite mission that has been providing measurements of incoming solar x-ray, ultraviolet, visible, near-infrared, and total solar radiation since April 2003. These measurements are key to enable advances in understanding the long-term solar influence of the Earth's climate. We are presenting the methods used for calibrating the SORCE Solar Irradiance Measurement (SIM) and for tracking the instrument degradation over the lifetime of the instrument.
The Solar Radiation and Climate Experiment (SORCE) is a NASA-sponsored Low-Earth-Orbit satellite mission
providing measurements of incoming x-ray, ultraviolet, visible, near-infrared and total solar radiation. SORCE is
currently in its 10th year of operation. The Spectral Irradiance Monitor (SIM) instrument has been providing daily solar
spectrum covering the wavelength range from 240 to 2400 nm at a resolution between 0.60-33 nm using a single optical
element. SIM was designed to provide an absolute accuracy of < 2% over the wavelength coverage and a goal of longterm
accuracy of 0.03% per year. The exposure of the optics, detectors and electronics to the harsh space environment
causes changes in their properties. With the very high accuracy goals, it is critical to keep track of these changes as
precisely as possible throughout the lifetime of the mission.
We will be reviewing the methods used to track and correct for SIM instrumental degradation of the optics and the
detectors since the start of the mission. We will also discuss lessons learned in the design of long lived solar observing
missions and how they were applied to the SIM instrument on the coming Total Solar Irradiance Sensors (TSIS) mission.
John Wilson, F. Hearty, M. Skrutskie, S. Majewski, R. Schiavon, D. Eisenstein, J. Gunn, J. Holtzman, D. Nidever, B. Gillespie, D. Weinberg, B. Blank, C. Henderson, S. Smee, R. Barkhouser, A. Harding, S. Hope, G. Fitzgerald, T. Stolberg, J. Arns, M. Nelson, S. Brunner, A. Burton, E. Walker, C. Lam, P. Maseman, J. Barr, F. Leger, L. Carey, N. MacDonald, G. Ebelke, S. Beland, T. Horne, E. Young, G. Rieke, M. Rieke, T. O'Brien, J. Crane, M. Carr, C. Harrison, R. Stoll, M. Vernieri, M. Shetrone, C. Allende-Prieto, J. Johnson, P. Frinchaboy, G. Zasowski, A. Garcia Perez, D. Bizyaev, K. Cunha, V. Smith, Sz. Meszaros, B. Zhao, M. Hayden, S. D. Chojnowski, B. Andrews, C. Loomis, R. Owen, M. Klaene, J. Brinkmann, F. Stauffer, D. Long, W. Jordan, D. Holder, F. Cope, T. Naugle, B. Pfaffenberger, D. Schlegel, M. Blanton, D. Muna, B. Weaver, S. Snedden, K. Pan, H. Brewington, E. Malanushenko, V. Malanushenko, A. Simmons, D. Oravetz, S. Mahadevan, S. Halverson
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) uses a dedicated 300-fiber, narrow-band
near-infrared (1.51-1.7 μm), high resolution (R~22,500) spectrograph to survey approximately 100,000 giant stars across
the Milky Way. This three-year survey, in operation since late-summer 2011 as part of the Sloan Digital Sky Survey III
(SDSS III), will revolutionize our understanding of the kinematical and chemical enrichment histories of all Galactic
stellar populations. We present the performance of the instrument from its first year in operation. The instrument is
housed in a separate building adjacent to the 2.5-m SDSS telescope and fed light via approximately 45-meter fiber runs
from the telescope. The instrument design includes numerous innovations including a gang connector that allows
simultaneous connection of all fibers with a single plug to a telescope cartridge that positions the fibers on the sky,
numerous places in the fiber train in which focal ratio degradation had to be minimized, a large mosaic-VPH (290 mm x
475 mm elliptically-shaped recorded area), an f/1.4 six-element refractive camera featuring silicon and fused silica
elements with diameters as large as 393 mm, three near-infrared detectors mounted in a 1 x 3 mosaic with sub-pixel
translation capability, and all of these components housed within a custom, LN2-cooled, stainless steel vacuum cryostat
with dimensions 1.4-m x 2.3-m x 1.3-m.
As a proof-of-concept, we have constructed and tested a cryogenic polarimeter in the laboratory as a prototype
for the MUSIC instrument (Multiwavelength Sub/millimeter Kinetic Inductance Camera). The POLOCAM
instrument consists of a rotating cryogenic polarization modulator (sapphire half-waveplate) and polarization
analyzer (lithographed copper polarizers deposited on a thin film) placed into the optical path at the Lyot stop
(4K cold pupil stop) in a cryogenic dewar. We present an overview of the project, design and performance
results of the POLOCAM instrument (including polarization efficiencies and instrumental polarization), as well
as future application to the MUSIC-POL instrument.
The Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) uses a large-format cross delay line
(XDL) detector in its Far Ultraviolet (FUV) channel. While obtaining spectra, light falls non-uniformly on the detector
due to the optical design and the spectral properties of the object being observed; in particular, bright emission lines
from geocoronal Lyman-alpha can fall on the detector in more than 20 locations. As a result, some areas of the detector
have received a much greater exposure than others. This non-uniform illumination has led to a time- and position-dependent
change in the gain of the microchannel plates, which causes variations in the overall detector performance.
We will discuss the effects of this gain sag on the science data, and discuss mitigation strategies which are being
implemented in order to maximize the detector lifetime.
The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope (HST) during Servicing
Mission 4 (SM4) in May 2009. COS is designed to obtain spectra of faint objects at moderate spectral resolution (R >
16,000) in two channels: FUV, covering wavelengths from 1150 to 1450 Å; and NUV, covering 1700 - 3200 Å. Two
low resolution gratings (R > 1500) cover the < 900 - 2050 Å (FUV) and 1650 - 3200 Å (NUV) wavelength regions. An
imaging capability is also available on the NUV channel.
As part of the Hubble Servicing Mission Observatory Verification (SMOV) program, an extensive period of checkout,
fine-tuning and preliminary characterization began after the installation of COS. The COS SMOV program was a
cooperative effort between the Space Telescope Science Institute and the Instrument Definition Team based at the
University of Colorado. Nearly 2800 COS exposures in 34 separate observing programs were obtained during the course
of SMOV. Early activities included an initial instrument functional checkout, turn-on and initial characterization of the
detectors, NUV and FUV channel focus and alignment, and target acquisition verification and assessment. Once this
initial period was completed, science-related calibrations and verifications were performed in order to prepare the
instrument for normal science operations. These activities included wavelength calibration, flux calibration, detector flat
field characterization, spectroscopic performance verification, high S/N operation, and thermal and structural stability
measurements. We discuss the design, execution and results of the SMOV program, including the interrelationships
between the various tasks, and how the pre-launch plan was adjusted in real-time due to changing conditions.
The Cosmic Origins Spectrograph (COS) was installed on the Hubble Space Telescope (HST) in May 2009 during
Servicing Mission 4 (SM4). This paper discusses the initial on-orbit performance of the HST-COS far ultraviolet (FUV)
detector designed and built by the Experimental Astrophysics Group at the Univ. of California, Berkeley. The HST-COS
FUV detector is an open face, photon counting, microchannel plate (MCP) based device employing a cross delay
line (XDL) readout. The detector consists of two separate, end-to-end segments (2x 85mm x 10mm - 179mm x 10mm
total with a gap between segments), each digitized within a 16384x1024 space. The input surface is curved to match the
Rowland circle of HST-COS. The CsI photocathode and open face nature result in sensitivity from <900Å to ~1750Å.
Spatial resolution is approximately 25-30μm. Comparisons of on-orbit behavior relative to expectations from ground
testing are performed. Areas of discussion include background (rate and morphology), sensitivity (system throughput
and short wavelength response), and imaging performance (apparent spatial resolution and flat field fixed pattern). A
measured increase in the MCP gain relative to ground testing is also discussed.
The Cosmic Origins Spectrograph,1 COS, will be installed in the Hubble Space Telescope (HST) during the next
servicing mission. This will be the most sensitive ultraviolet spectrograph ever flown aboard the HST.
The calibration pipeline (CALCOS), written in Python, has been developed by the Space Telescope Science
Institute (STScI) to support the calibration of HST/COS data. As with other HST pipelines, CALCOS uses an
association table to specify the data files to be included, and employs header keywords to specify the calibration
steps to be performed and the reference files to be used.
CALCOS is designed with a common underlying structure for processing far ultraviolet (FUV) and near
ultraviolet (NUV) channels which, respectively, use a cross delay line and a Multi Anode Microchannel Array
(MAMA) detector. The pipeline basics and channel dependent specifics are presented. The generation and
application of the current reference files, derived from ground-based calibration data, is described, along with
the pipeline verification process and results.
The CALCOS calibration includes pulse-height filtering and geometric correction for the FUV channel; flat-field,
deadtime, and Doppler correction for both channels. Methods for obtaining an accurate wavelength calibra-tion
using the on-board spectral line lamp are described. The instrument sensitivity is applied to the background
corrected spectrum to produce the final flux calibrated spectrum.
We have completed a conceptual design study of the High Resolution Optical Spectrograph for the Thirty Meter Telescope project. We propose the use of a fiber fed integral field unit and a dichroic tree to achieve R=100,000 spectroscopy from 310 to 1100 nm independent of AO performance. The system relies on the dichroic tree to provide coarse wavelength selection, and 32 first order spectro-graph benches. This approach allows for simultaneous optimization of grating and detector performance for all wavelengths, resulting in high efficiency, near uniform dispersion, and reduced program risk and cost due to the high degree of component commonality. We present projected performance and design details.
We present a conceptual design for a High Resolution Optical Spectrograph (HROS) for the Thirty Meter Telescope, a 30-m primary aperture ground-based telescope currently under development (www.tmt.org). To decouple downstream optics sizes from the size of the seeing disk and/or AO performance, we use fiber fed IFUs to generate a 0.1" pseudo-slit. The use of multiple IFUs instead of a slit also allows for spatially resolved spectroscopy, multi-object spectroscopy, positionable sky sampling, and insertion of a simultaneous wavelength calibration signal into the beam. Instead of a cross-dispersed echelle design, our concept uses a dichroic tree to provide spectral separation. The dichroics feed 32 independent first-order spectrographs that cover the 310 to 1100 nm optical waveband at a nominal spectral resolution of R=100,000. This approach allows for the optimization of coatings and on-blaze grating performance in each channel, resulting in high efficiency, near-uniform dispersion, and reduced program risk and cost due to the high degree of component commonality. We also discuss the general applicability of this concept for achieving high resolution spectroscopy in the next generation of ground-based instrumentation.
We are presenting the preliminary characterization results of the Rockwell Scientific HgCdTe detector array used in the Near Infrared Camera and Fabry-Perot Spectrograph (NIC-FPS). The detector was fabricated to cover the wavelength range from 0.8 to 2.5 microns and is bonded to a Hawaii-1RG multiplexer. This instrument was designed and built at the University of Colorado in Boulder and is used at the Apache Point Observatory's 3.5 meter telescope.
A second generation near-infrared instrument was built by the University of Colorado for the ARC 3.5 meter telescope and is being commissioned at the Apache Point Observatory. An initial engineering run, first light, commissioning observations, and initial facility science operations have been accomplished in the last year. Instrument imaging performance was good to excellent from first light and consortium observers began to employ the instrument on a shared-risk basis immediately after commissioning operations. Instrument optical and mechanical performance during this testing and operations phase are discussed. Detector system (Rockwell Hawaii-1RG 1024x1024 HgCdTe focal plane array with Leach controller) characteristics during these early operations are detailed along with ongoing efforts for system optimization. High resolution (R~10,000) spectroscopy is planned employing a Queensgate (now IC Optical) cryogenic Fabry-Perot etalon, though mechanical difficulties with the etalon precluded a system performance demonstration. The Consortium has decided that the instrument will retain the name NIC-FPS (Near Infrared Camera and Fabry-Perot Spectrometer) after commissioning.
A near-infrared instrument is being built for the ARC 3.5 meter telescope that will operate in both an imaging and a narrow band, full field spectroscopic mode. The 4.5' x 4.5' fild-of-view is imaged onto a new-generation, low-noise Rockwell Hawaii-1RG 1024x1024 HgCdTe detector. High resolution (R~10,000) spectroscopy is accomplished by employing a Queensgate (now IC Optical) cryogenic Fabry-Perot etalon. The instrument is housed in a large Dewar of innovative, light-weight design. This report describes the as-built opto-mechanical system for the instrument and the work remaining before deployment at Apache Point Observatory in New Mexico.
We present the preliminary calibration results for the Cosmic Origins Spectrograph, a fourth generation replacement instrument for the Hubble Space Telescope due to be installed in mid-2005. The Cosmic Origins Spectrograph consists of two spectroscopic channels: a far ultraviolet channel that observes wavelengths between 1150 and 2000 Åand a near ultraviolet channel that observes between 1700 and 3200 Å. Each channel supports moderate (R≈20,000) and low (R≈2000) spectral resolution. We discuss the calibration methodology, test configurations, and preliminary end-to-end calibration results. This includes spectral resolution, system efficiency, flat fields, and wavelength scales for each channel. We also present the measured transmission of the Bright Object Aperture (BOA) and the measured spatial resolution.
The Near-Infrared Camera and Fabry-Perot Spectrometer (NIC-FPS) will provide near-IR imaging over the wavelength range ~0.9-2.45 microns and medium resolution (R~10,000) full-field Fabry-Perot spectroscopy in the 1.5-2.4 micron range. Science observation will commence by mid 2004 on the Astrophysical Research Consortium 3.5-m telescope at the Apache Point Observatory in Sunspot, NM.
NIC-FPS will allow a wide variety of extragalactic, galactic, and solar system observational programs to be conducted. NIC-FPS will support two observational modes, near-IR imaging or Fabry-Perot spectroscopy. For spectroscopy of line-emitting objects, the cryogenic Fabry-Perot etalon is inserted into the optical path to generate 3D spectral datacubes at ~30 km/s spectral resolution. For narrow to broad-band imaging, the etalon is removed from the optical path. Both modes will utilize a Rockwell Hawaii 1RG 1024 x 1024 HgCdTe detector which features low dark current, low noise and broad spectral response required for astronomical observations. The optics and detector will provide a full 4.6' × 4.6' field of view at 0.27" pixel. NIC-FPS will be mounted to the ARC telescope's Nasmyth port.
NIC-FPS will significantly increase ARC's near-IR imaging and spectroscopy capabilities. We present NIC-FPS's optical design and instrument specifications.
KEYWORDS: Sensors, Calibration, Electronics, Doppler effect, Analog electronics, Spectral calibration, Data processing, Dispersion, Spectrographs, Chemical elements
COS has two distinct ultraviolet channels covering the spectral range from 1150Å to 3200Å. The NUV channel covers the range from 1700Å to 3200Å and uses the Hubble Space Telescope's STIS spare MAMA. The FUV channel uses a micro channel plate detector with a cross-delay line readout system to cover the range from 1150Å to 1900Å. Due to the analog nature of the readout electronics of the FUV detector, this system is sensitive to temperature variations and has non-uniform pixel size across its sensitive area. We present a step-by-step description of the calibration process required to transform raw data from the COS into fully corrected and calibrated spectra ready for scientific analysis. Initial simulated raw COS data is used to demonstrate the calibration process.
The flight microchannel plate detectors to be used in the Cosmic Origins Spectrograph, a fourth generation instrument for the Hubble Space Telescope, have been calibrated in the laboratory before being integrated into the spectrograph. This paper presents the results of these calibrations that include measurements of the detector quantum efficiency, spatial resolution, spatial linearity, flat field, electronic livetime and the local count rate limit.
Time-delay anodes are typically used in conjunction with microchannel plates to provide photon counting and two- dimensional imaging. The anode and associated electronics are used to compute the centroid of the charge cloud from the microchannel plate stack. The computation is done in analog circuitry and reported as a digital value. The analog nature of the time-delay anode makes them susceptible to variations in the correlation between physical space and the reported digital value. These variations, both local and global, must be corrected as part of the data reduction of scientific data. If left uncorrected in spectral data, for example, these variations would result in inaccurate wavelength identifications and distorted spectral line profiles. This work describes successful algorithms for correcting the dominant distortions present in a time-delay anode; geometric (local) and thermal (global) distortions. These algorithms were developed as part of the data reduction pipelines for the Cosmic Origins Spectrograph (COS), a fourth generation instrument for the Hubble Space Telescope, and the Far Ultraviolet Spectroscopic Explorer (FUSE).
Francois Roddier, Lennox Cowie, J. Elon Graves, A. Songaila, Daniel McKenna, Jean Vernin, Max Azouit, J. Caccia, Eric Limburg, Claude Roddier, Derrick Salmon, Stephane Beland, David Cowley, S. Hill
During two short campaigns intensive coordinated measurements have been performed to determine the various contributions to image degradation on Mauna Kea. Some of the results already obtained are presented here.
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