Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder Mission: Status Overview

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a Tier 1 mission recommended by the NRC Decadal Survey 2007. The foundation of CLARREO is the ability to produce highly accurate climate records to test climate projections in order to improve models and enable sound policy decisions. The CLARREO mission accomplishes this critical objective through accurate SI-traceable decadal observations that are sensitive to many of the key climate parameters such as radiative forcings, climate responses, and feedbacks. Uncertainties in these parameters drives uncertainty in current climate model projections. In 2016, the CLARREO project received funding for a Pathfinder mission to demonstrate essential measurement technologies required for the full mission. The appropriated funds support the flight of one instruments -- a Reflected Solar (RS) spectrometer, hosted on the International Space Station (ISS) in the 2020 time frame. The CLARREO Pathfinder (CPF) payload will be integrated with the ExPA with location on the ISS, slotted on the ExPRESS logistics carrier (ELC-1). The CPF provides high accuracy spectral reflectance measurements using an RS spectrometer operating between 350 and 2300 nm with continuous spectral coverage (\u3e 95% of reflected solar energy) with uncertainty \u3c 1% (k=2). The reflected solar spectrometer will be capable of pointing to the moon and sun for calibration, as well as tracking time/angle/space-matched observations for reference inter-calibration of other on-orbit radiometers and surface sites. The CPF will provide Earth nadir observations between 52 N and 52 S latitude with full diurnal cycle sampling in approximately 1 month. The CPF will reduce risks of the full CLARREO mission by demonstrating higher accuracy, SI-traceablity, on-orbit calibration approaches and demonstrating that high-accuracy reference inter-calibration with other on-orbit sensors (CERES, VIIRS, CrIS) is achievable