CLARREO

Due to funding cuts in announced for the 2012 budget, the CLARREO mission was significantly scaled back, while remaining spaceborne projects were eyed to fill the gap. In the President's FY16 budget request, a smaller CLARREO Pathfinder (CPF) mission was provided $76.9M to demonstrate essential measurement technologies of the CLARREO Tier 1 Decadal Survey mission. That funding will potentially support the flight of the Reflected Solar (RS) spectrometer, which is one piece of the full Decadal Survey-recommended mission, hosted on the International Space Station (ISS) in 2020 (although the Trump administration's budget proposal of March 2017 appears set to defund this mission). Below is the mission concept presented at the Mission Concept Review in November 2010. CLARREO was then envisioned to consist of four observatories on two dual-manifested launches on Minotaur IV+ vehicles. Alternative mission concepts were developed to accommodate reduced available funding. A CLARREO mission on the International Space Station, to include one each of the RS and IR spectrometers, was found to provide the best science value for the lowest feasible cost. Due to the ISS orbital inclination of 51.65 degrees, CLARREO on ISS measurements would not include the polar regions, resulting in the mission being unable to track global spectral benchmarks compared to the version of the mission presented at the Mission Concept Review. In 2016, a Pathfinder mission to the full CLARREO mission received funding. 'The allocated funds support the flight of a Reflected Solar (RS) spectrometer, hosted on the International Space Station (ISS) in the 2020 time frame. ... The CPF is a Class D mission with 1 year of operations on orbit and 1 year for analysis of acquired data.' The mission is designed to demonstrate essential measurement technologies in orbit that can be used to reduce the risk of a full CLARREO mission. CLARREO Pathfinder has two primary objectives: to demonstrate high accuracy on orbit traceable to International Systems of Units (SI) and to transfer that accuracy to other spaceborne sensors. Pathfinders threshold objective compared to the full baseline CLARREO mission is relaxed by a factor of two from 0.15% to 0.3% (k=1). CLARREO could make highly accurate decadal change observations that are traceable to International Systems of Units (SI) standards. For example, at solar wavelengths this is intended to be confirmed after launch using comparison of actual data to theoretical simulations of lunar/solar radiance generated within a high-fidelity sensor model, although it is unclear how such a non-experimental approach will ensure SI traceability. The Earth observations then made by CLARREO have sensitivity to the most critical but least understood climate radiative forcings, responses, and feedbacks, such as: Current satellite-based sensors are not designed to meet the accuracy requirements needed for climate change detection. Many sensors used for climate measurements were designed to meet operational weather needs and are not optimized for climate sampling. These sensors, along with older instruments designed for climate, lack the on-board ability to test for systematic errors on orbit. The CLARREO mission will meet these goals through careful consideration of the instrument design, calibration traceability at all stages of development and operation, with spectral, spatial and temporal sampling focused specifically on the creation of climate records. Then after development of new cross-calibration methodologies far more accurate than those achieved today, CLARREO may serve as an in-orbit standard to provide reference intercalibration for missions like the broadband Clouds and the Earth's Radiant Energy System (CERES), operational sounders including the Cross-track Infrared Sounder (CrIS) and Infrared Atmospheric Sounding Interferometer (IASI), and imagers such as the Visible Infrared Imaging Radiometer Suite (VIIRS) and Advanced Very High Resolution Radiometer (AVHRR). The 2007 National Research Council (NRC) Decadal Survey report, 'Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond,' provides the basis for the future direction of NASA’s space-based Earth observation system. Missions were ranked according to scientific merit, contributions to long-term observational records, societal benefits, affordability, and technological readiness. The four missions recommended for earliest implementation by NASA were classified as “Tier 1” missions and included CLARREO. The NRC Decadal Survey concluded that the single most critical issue for current climate change observations was their lack of accuracy and low confidence in observing the small climate change signals over decade time scales. CLARREO observations of climate change on decadal scales address this issue by achieving the required levels of accuracy and traceability to SI standards for a set of observations sensitive to a wide range of key climate change observations.