LASP To Play Major Role In CLARREO Pathfinder Mission

An artist’s conception of the CLARREO Pathfinder on ISS Reflected Solar Instrument depicting Earth, solar, lunar, and cross-calibration modes of operation. Image Credit: LASP

December 16, 2016 – The University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics (LASP) is playing a major role in the groundbreaking Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder mission, scheduled to deploy on the International Space Station (ISS) by 2020. The mission will substantially improve the accuracy of Earth radiation measurements that will advance our ability to detect climate change and identify its causes.

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.

LASP was selected to build CLARREO’s Reflected Solar (RS) instrument due to the success of the Hyperspectral Imager for Climate Science instrument (HySICS) developed and balloon-flight-tested under NASA’s Instrument Incubator Program and based on the Earth Climate Hyperspectral Observatory (ECHO) proposal to the NASA Earth Ventures program, which was favorably rated as “selectable.”

One of the critical differences of this instrument relative to others in orbit is its ability to point the entire instrument at Earth, Sun (every 2 weeks), Moon (monthly at 5 to 10 degree phase angle), or deep space. This eliminates the need for scanning mirrors with angle dependent calibration uncertainties, and allows the use of depolarizers to reduce polarization sensitivity to the required levels. Scanning the instrument view across lunar and solar disks provides images suitable for verifying stray light performance.

CLARREO concepts for improved SI-traceable absolute accuracy in orbit. The verification of nadir spectral reflectance accuracy relies on rotating the entire instrument to view the Moon at constant phase angle as a single-level stable reflectance source, similar to the SeaWiFS approach, the Sun in combination with filters and precision apertures for nonlinearity determination, and the use of depolarizers to control polarization sensitivity.

The RS instrument will measure solar radiation reflected from Earth in wavelength bands covering most of the solar spectrum. Its improved accuracy will enable the calibration of other climate sensors, setting the stage to monitor climate change from space, identify its underlying causes, and improve models to enable sound policy decisions.

LASP received the Pre-Phase A study award in June and will begin building the RS instrument in March 2017.