SORCE Solar Irradiance
Data Products Douglas M. Lindholm, Christopher K. Pankratz,
Solar Spectral Irradiance (SSI)
Barry G. Knapp, Juan Fontenla, Jerald W. Harder, William E. McClintock, Greg Kopp, Martin Snow,
Thomas N. Woods
Total Solar Irradiance (TSI)
Product Overview
Solar Radiation and Climate Experiment (SORCE)
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• The TIM instrument measures the TSI, monitoring changes in incident sunlight
to the Earth's atmosphere using four ambient­temperature active cavity
radiometers
• The TSI product contains science results for the entire SORCE mission.
Updates to Level 3 TSI data at the SORCE WWW site occur daily.
• Level 3 science data products consist of daily and 6­hourly average irradiances
at 1 astronomical unit (AU) for solar studies and at the true Sun­Earth distance for Earth climate studies.
• To construct these released products, high time cadence measurements
(every 50 seconds) from the TIM instrument are averaged to produce
representative daily and 6­hourly values of the TSI.
• Shuttered operation of the instrument corrects for thermal background, and
state­of­the­art phase sensitive detection algorithms applied to the data at the
shutter fundamental reduce noise and sensitivity to drifts. NASA sponsored satellite mission to study solar irradiance
Spacecraft launched January 25, 2003
Data Product Summary
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Total Solar Irradiance (TSI), W/m²
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Daily and 6­Hourly Mean Irradiances. Provided by the TIM Instrument
Solar Spectral Irradiance (SSI), W/m²/nm
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Daily Irradiance spectra from 115­2400 nm, normalized to 1 AU
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Measurements from the SIM, SOLSTICE, and XPS instruments
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XPS: 0.1 ­ 34 nm at 5­10 nm intervals, 6­channels
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SOLSTICE: 115 ­ 310 nm at 1 nm intervals
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SIM: 310 ­ 2400 nm at fixed wavelengths with 1­34 nm resolution
Data Access
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• The SORCE SOLSTICE, SIM, and XPS instruments together provide measurements
of the full­disk Solar Spectral Irradiance (SSI) from ~0.1 nm to 2400 nm (excluding
34­115 nm)
• Daily average irradiances are available, reported at a mean solar distance of 1
astronomical unit (AU)
doug.lindholm@lasp.colorado.edu Overview
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Product Overview
SORCE Web Site: http://lasp.colorado.edu/sorce/
LISIRD: http://lasp.colorado.edu/lisird/
GES DISC: http://disc.sci.gsfc.nasa.gov
Data Quality / Status
Abstract
The Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado manages the Solar Radiation and Climate Experiment (SORCE) Science Data System. This data processing system routinely produces Total Solar Irradiance (TSI) and Spectral Solar Irradiance (SSI) data products, which are formulated using measurements from the four primary instruments on board the SORCE spacecraft along with calibration data and other ancillary information to correct for all known instrumental and operational factors. The TIM instrument provides measurements of the TSI, whereas the SIM, SOLSTICE, and XPS instruments collectively provide measurements of the solar irradiance spectrum from 1 nm to 2400 nm (excluding 31­115 nm, which is measured by the SEE instrument on NASA's TIMED mission). "Level 3" data products (time­averaged over daily and six­hourly periods and/or spectrally re­
sampled onto uniform wavelength scales) are routinely produced and delivered to the public via the SORCE web site (http://lasp.colorado.edu/sorce/data/), and are archived at the Goddard Earth Sciences (GES) Data and Information Services Center (DISC). The SORCE data are also available from LASP Interactive Solar Irradiance Datacenter (LISIRD) web site which provides access to over 25 years of LASP's solar irradiance measurements and is evolving to become the ultimate source of solar irradiance data products. This poster provides an overview of the SORCE solar irradiance data products, including quality and availability, as well as current and planned data access capabilities.
• Version 10 data, including minor updates to instrument degradation correction
and servo gain calibration, are currently available and updated daily.
•The TIM instrument is proving very stable with on­orbit solar exposure, and
long­term relative uncertainties are estimated to be less than
0.014 W/m2/yr (10 ppm/yr).
• Present absolute accuracy is estimated to be approximately 0.48 W/m2 (350
ppm), largely determined by uncertainties in the applied power linearity. This
is consistent with the agreement between all four TIM cones.
• There remains an unresolved 4.5 W/m2 difference between the TIM and other
radiometers, which is being studied by the TSI and radiometry communities.
Recent comparisons of a ground­based SORCE/TIM instrument with a NIST
calibrated cryogenic radiometer in the new TSI Radiometer Facility support the lower TSI value reported in the SORCE TIM data products.
• Data are routinely available 7 days after the measurements are made.
• On­orbit instrument characterization is an ongoing effort, although only minor
corrections are anticipated at this phase in the SORCE TIM mission.
SORCE TSI Time Series
SORCE TSI Degradation
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After over 7 years on orbit, the TIM instrument remains stable with on­orbit degradation calibrations (which are corrected by data processing) showing only 150 ppm degradation, which is less than any other flight TSI instrument.
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Version 10 XPS data are currently available and updated daily. These data are known
to be of good quality and are appropriate for research and/or publication.
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The revised XPS Level 4 algorithm provides more accurate results for flare events [Woods et al., 2008]
Official gateway to SORCE information and data products
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Provides access to various solar irradiance and related data products and tools GES DISC (http://disc.sci.gsfc.nasa.gov/SORCE/)
Permanent archive References
Direct download of data product files in several formats and IDL routines
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Interactive plotting: zoom to explore and select range of data to download
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Multiple download format options
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Data served by the LASP Time Series Server (LaTiS) using OPeNDAP protocols
Coming Soon
Improved hardware and software infrastructure
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Access to additional data products
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Remote, programmatic (e.g. IDL) access to data via LaTiS
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Current Development and Plans
Enhanced metadata (THREDDS, SPASE) with browse and query capabilities
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Increased interoperability with other Virtual Observatories
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Tools to facilitate data analysis, visualization, integration, and inter­comparison
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Managed by the SORCE Science Team
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Provides direct access to SORCE data products and information
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Merged mission length files are available for easy download
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Data products are available within 7 days of measurement
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o Version 10 SOLSTICE data are currently available and updated daily. Version 10
data, with improved calibration corrections, will be released soon.
o Absolute Accuracy: (See McClintock et. al 2005 calibration paper, p. 288 for
details.)
• FUV (115­180 nm): Varies from ~6% at shortest wavelengths to ~2% at longer
wavelengths.
• MUV (180­310 nm): ~3% at wavelengths <300 nm; ~6% longward of 300 nm.
o Relative Accuracy:
• FUV (115­180 nm) – Less than 0.5% per year
• MUV (180­310 nm) – Less than 0.5% per year
• Data Quality / Status:
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http://lasp.colorado.edu/sorce/data/
• Data Quality / Status:
discrete bandpasses) and at 121.6 (H I Lyman­α).
• Of all the SORCE instruments, the XPS is most sensitive to flare events on the Sun
as the solar XUV radiation often changes by a factor of 2 to 10, or more, during
flares.
Current Capabilities
SORCE Data Access
FUV and MUV spectrometers.
• SOLSTICE provides precise daily measurements of solar spectral irradiance at
ultraviolet wavelengths from 115 nm to 310 nm with a native spectral resolution of
approximately 0.1 nm
• SOLSTICE makes daily solar irradiance measurements and compares them to the
irradiance from an ensemble of 18 stable early­type stars. This approach provides an
accurate monitor of instrument in­flight performance and provides a basis for solarstellar
irradiance comparison for future generations.
• Onboard sensitivity calibration is maintained by observing stable early­type stars.
• The XPS measures the solar soft x­ray (XUV) irradiance from 0.1 to 34 nm (in 5
LISIRD (http://lasp.colorado.edu/lisird/)
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Solar­Stellar Irradiance Comparison Experiment (SOLSTICE)
XUV Photometer System (XPS)
SORCE Web Site (http://lasp.colorado.edu/sorce/)
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o Version 17 SIM data are currently available and updated daily.
o Absolute Accuracy: The absolute accuracy of SIM data is about 2%.
o Relative Accuracy: The uncertainties reported with the data provide an indicator
of relative precision. Above 500 nm, relative accuracy is better than approximately
300 ppm. Below 500 nm, relative accuracy decreases to approximately 0.5% at 310 nm.
o Wavelength Scale: SIM wavelengths (310­2400 nm) are presently estimated to
be accurate to 0.02 nm ± λ*1.5x10­4 (0.05 ­ 0.2 nm), depending on wavelength
o Further refinements of the degradation corrections are being worked on for times after about April 1, 2008.
• There are two redundant SOLSTICE instruments on the SORCE spacecraft, each with
SORCE standard data products are available via the SORCE web site, the LASP Interactive Solar IRradiance Data center (LISIRD), and from the Goddard Earth Sciences (GES) Data and Information Services Center (DISC).
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• SIM is a Fèry Prism Spectrometer which measures solar irradiance from 310 nm to
2400 nm with a spectral resolution varying from 1 to 34 nm
• SIM contains four focal plane photodiodes for routine measurements. Absolute
calibration is maintained using the onboard Electrical Substitution Radiometer (ESR)
detector, which operates on the same principal and uses the same detector
methodology as the active cavity radiometer in the SORCE TIM instrument
• Data Quality / Status:
Data Access and Services
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Spectral Irradiance Monitor (SIM)
LASP Interactive Solar Irradiance Data Center (LISIRD) New look and capabilities: http://lasp.colorado.edu/lisird/
Interactive plots and data access ➔
Download format options
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Unified access to varied solar irradiance data products:
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Solar irradiance measurements
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Composite data products
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Reference spectra
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Model derived products
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Space weather products
Harder, Jerald, George Lawrence, Juan Fontenla, Gary Rottman, and Thomas Woods, “The Spectral Irradiance Monitor: Scientific Requirements, Instrument Design, and Operation Modes”, Solar Physics, 203, 1, 141­167, 2005.
Harder, Jerald W., Juan Fontenla, George Lawrence, Thomas Woods, and Gary Rottman, “The Spectral Irradiance Monitor: Measurement Equations and Calibration”, Solar Physics, 203, 1, 169­203, 2005.
Kopp, Greg and George Lawrence, “The Total Irradiance Monitor (TIM): Instrument Design”, Solar Physics, 203, 1, 91­109, 2005.
Kopp, Greg, Karl Heuerman, and George Lawrence, “The Total Irradiance Monitor (TIM): Instrument Calibration”, Solar Physics, 203, 1, 111­127, 2005.
Kopp, Greg, George Lawrence, and Gary Rottman, “The Total Irradiance Monitor (TIM): Science Results”, Solar Physics, 203, 1, 129­140, 2005.
McClintock, William E., Gary J. Rottman, and Thomas N. Woods, “Solar Stellar Irradiance Comparison Experiment II (SOLSTICE II): Instrument Concept and Design”, Solar Physics, 203, 1, 225­258, 2005.
McClintock, William E., Martin Snow, and Thomas N. Woods, “Solar Stellar Irradiance Comparison Experiment II (SOLSTICE II): Pre­Launch and On­
Orbit Calibrations”, Solar Physics, 203, 1, 259­294, 2005.
Pankratz, Christopher K., Barry G. Knapp, Randy A. Reukauf, Juan Fontenla, Michael A. Dorey, Lillian M. Connelly, and Ann K. Windnagel, “The SORCE Science Data System”, Solar Physics, 203, 1, 389­413, 2005.
Woods, T. N., P. C. Chamberlin, W. K. Peterson, R. R. Meier, P. G. Richards, D. J. Strickland, G. Lu, L. Qian, S. C. Solomon, B. A. Iijima, A. J. Mannucci, and B. T. Tsurutani, XUV Photometer System (XPS): Improved irradiance algorithm using CHIANTI spectral models, Solar Physics, 249, doi 10.1007/s11207­008­9196­6, 2008. Woods, Thomas N., Gary Rottman, and Robert Vest, “XUV Photometer System (XPS): Overview and Calibrations”, Solar Physics, 203, 1, 345­374, 2005.
Woods, Thomas N. and Gary Rottman, “XUV Photometer System (XPS): Solar Variations During the SORCE Mission”, Solar Physics, 203, 1, 375­387, 2005.