NPOESS Solar Irradiance Monitoring for Climate Change

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) is the next generation of polar environmental satellites. It combines the missions of the DoD's Defense Meteorological Satellite Program (DMSP) and the DoC's NOAA Polar Operational Environmental Satellite (POES). One of the new sensors for the NPOESS program is the Total and Spectral Irradiance Sensor (TSIS), which will monitor the solar forcing at the top of the Earth's atmosphere. It is now clear that natural climate variability must be considered when studying and predicting anthropogenic effects on climate. Solar and volcanic activities are the two primary natural climate forcers. Relative changes in the solar irradiance at different wavelengths are also important. UV solar irradiance is a key component in both the production and loss of stratospheric ozone. Infrared irradiance is important in the thermal structure of the troposphere. Monitoring both the total irradiance and the spectral irradiance from NPOESS will provide critical information on future climate change. Because the changes in solar irradiance are relatively small and occur on decadal time scales, the stability requirements on these sensors are demanding. In this presentation, we will review the NPOESS TSIS sensors and their performance requirements. The TSIS performance will be compared to the performance of similar instruments presently operating on the NASA SOlar Radiation and Climate Experiment (SORCE) mission.