Solar radiation is the dominant, direct energy input into the terrestrial ecosystem; and it affects all physical, chemical, and biological processes. The Sun provides a natural influence on the Earth’s atmosphere and climate. In order to understand mankind’s roles in climate change, the Sun’s impact must first be understood.
The Solar Radiation and Climate Experiment (SORCE) measures the Sun’s output with the use of state-of-the-art radiometers, spectrometers, photodiodes, and photomultiplier tubes engineered into instruments mounted on a satellite observatory. SORCE is a free-flying, Earth-orbiting satellite carrying four instruments to measure the solar radiation incident at the top of the Earth’s atmosphere. Spectral measurements identify the irradiance of the Sun by characterizing the Sun’s energy over the full spectral range from ultraviolet to infrared. Data obtained by the SORCE experiment is used to model the Sun’s output and to explain and predict the effect of the Sun’s radiation on the Earth’s atmosphere and climate.
- The Total Irradiance Monitor (TIM), the Spectral Irradiance Monitor (SIM), Solar Stellar Irradiance Comparison Experiment (SOLSTICE), and the X-ray Ultraviolet Photometer System (XPS)
- SORCE satellite and instrument mission operations
- Acquisition, management, processing, and distribution of the science data
- SORCE Mission Principal Investigator, Tom Woods
- Original SORCE mission Principal Investigator, Gary Rottman (retired 2005)
LASP developed and built the four science instruments on-board SORCE:
The TIM instrument measures the total solar irradiance (TSI), the spatially and spectrally integrated solar radiation incident at the top of the Earth’s atmosphere. TIM continues a solar climate data record, which began from space in 1978 and is used to determine the sensitivity of the Earth’s climate to the natural effects of solar forcing. The TIM TSI measurements monitor the incident sunlight to the Earth’s atmosphere using an ambient temperature active cavity radiometer. Using electrical substitution radiometers (ESRs) and taking advantage of new materials and modern electronics, the TIM measures TSI to an estimated absolute accuracy of 350 ppm (0.035%). Relative changes in solar irradiance are measured to less than 10 ppm/yr (0.001%/yr), allowing determination of possible long-term variations in the Sun’s output.
The SIM instrument is a newly designed spectrometer that provides the first long-duration solar spectral irradiance measurements in the visible and near infrared (Vis/NIR). The wavelength coverage is primarily from 300 to 2400 nm, with an additional channel to cover the 200-300 nm ultraviolet spectral region to overlap with the SOLSTICE instrument. Understanding the wavelength-dependent variability throughout SIM’s wavelength range is of primary importance for long-term climate change studies on Earth. SIM is a single optical element Fèry prism spectrometer; only one optical element is needed to focus and disperse the light onto a series of detectors in the spectrometer’s focal plane. In this focal plane, four photodiode detectors and an electrical substitution radiometer (ESR) are used to detect solar radiation. SIM contains two completely independent and identical (mirror-image) spectrometers to provide redundancy and self-calibration capability.
SORCE SOLSTICE is a follow-on to the very successful SOLSTICE launched aboard the Upper Atmospheric Research Satellite (UARS) in 1991. The new SOLSTICE makes daily solar ultraviolet (115-320 nm) irradiance measurements and compares them to the irradiance from an ensemble of 18 stable early-type stars. This approach provides an accurate monitor of instrument in-flight performance and provides a basis for solar-stellar irradiance comparison for future generations.
The SORCE XPS, which evolved from earlier versions flown on SNOE and TIMED, extends the solar X-ray ultraviolet (XUV) irradiance measurements with improvements to accuracy, spectral range, and temporal cadence.
For more information about the SORCE mission and instruments, see:
Launch date: January 25, 2003
Launch location: Kennedy Space Center, Cape Canaveral, Florida
Launch vehicle: Pegasus XL
Mission target: Earth orbit
Mission duration: Eight years, with a four-year extension (granted in 2007)
Other organizations involved:
- NASA’s Goddard Space Flight Center (GSFC)
- Naval Research Laboratory