Abstract
In order to advance understanding of how natural and anthropogenic processes affect Earth’s climate it is critically important to maintain accurate, long-term records of climate forcing. These climate-data records are a time series of measurements of sufficient length, consistency, and continuity to determine true climate variability and change. Quantifying the solar irradiance (both total and spectral) provides the necessary constraint on the total energy input. In particular, the long-term, continuous measurements of solar spectral irradiance (SSI) are needed to characterize poorly understood wavelength-dependent climate processes. The strong reliance on radiative transfer modeling for interpretation and quantification of the deposition of solar radiation in the atmosphere makes it imperative that the spectral distribution of radiant energy entering the atmosphere be known to a high degree of absolute accuracy (tied to international standards). Major measurement challenges in quantifying the influence of SSI variability on climate are achieving sufficient radiometric absolute accuracy and then maintaining (on-orbit) the long-term relative accuracy of the data record.
The Total and Spectral Solar Irradiance Sensor (TSIS) Spectral Irradiance Monitor (SIM) is the next generation, space-borne SSI monitor that will fly as part of the dual agency (NASA/NOAA) Joint Polar Satellite System (JPSS) program scheduled for launch in late 2016. The instrument has been designed, characterized and calibrated to achieve unprecedented levels of measurement accuracy (<0.25% absolute) and on-orbit stability (0.01-0.05%/yr.) required to meet the needs of establishing the SSI climate data record across a continuous wavelength region spanning 200 – 2400 nm (96% of the total solar irradiance). The full characterization and calibration follows a measurement equation approach at the unit-level for full validation of the end-to-end performance at the instrument-level. Following this approach, we characterize the SIM instrument as an “absolute” sensor tied to a cryogenic radiometer traceable to the NIST Primary Optical Watt Radiometer (POWR), the primary US standard for radiant power measurements.
The Next Generation Solar Spectral Irradiance Monitor for the JPSS-TSIS Mission: Instrument Overview and Radiometric Performance
In order to advance understanding of how natural and anthropogenic processes affect Earth’s climate it is critically important to maintain accurate, long-term records of climate forcing. These climate-data records are a time series of measurements of sufficient length, consistency, and continuity to determine true climate variability and change. Quantifying the solar irradiance (both total and spectral) provides the necessary constraint on the total energy input. In particular, the long-term, continuous measurements of solar spectral irradiance (SSI) are needed to characterize poorly understood wavelength-dependent climate processes. The strong reliance on radiative transfer modeling for interpretation and quantification of the deposition of solar radiation in the atmosphere makes it imperative that the spectral distribution of radiant energy entering the atmosphere be known to a high degree of absolute accuracy (tied to international standards). Major measurement challenges in quantifying the influence of SSI variability on climate are achieving sufficient radiometric absolute accuracy and then maintaining (on-orbit) the long-term relative accuracy of the data record.
The Total and Spectral Solar Irradiance Sensor (TSIS) Spectral Irradiance Monitor (SIM) is the next generation, space-borne SSI monitor that will fly as part of the dual agency (NASA/NOAA) Joint Polar Satellite System (JPSS) program scheduled for launch in late 2016. The instrument has been designed, characterized and calibrated to achieve unprecedented levels of measurement accuracy (<0.25% absolute) and on-orbit stability (0.01-0.05%/yr.) required to meet the needs of establishing the SSI climate data record across a continuous wavelength region spanning 200 – 2400 nm (96% of the total solar irradiance). The full characterization and calibration follows a measurement equation approach at the unit-level for full validation of the end-to-end performance at the instrument-level. Following this approach, we characterize the SIM instrument as an “absolute” sensor tied to a cryogenic radiometer traceable to the NIST Primary Optical Watt Radiometer (POWR), the primary US standard for radiant power measurements.