Laser-based spectral and radiometric calibration of the clarreo imaging spectrometer

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) plans to observe climate change trends over decadal time scales to determine the accuracy of climate projections. The project relies on spaceborne earth observations of SI-traceable variables sensitive to key decadal change parameters. The mission includes a reflected solar instrument retrieving at-sensor reflectance over the 320 to 2300 nm spectral range with 500-m spatial resolution and 100-km swath. Reflectance is obtained from the ratio of measurements of the earth's surface to those while viewing the sun relying on a calibration approach that retrieves reflectance with uncertainties less than 0.3%. This level of uncertainty relies on a mature spectrometer design, well-known instrument model, and detector-based calibration standards for prelaunch characterization. This paper presents calibration results that rely on laser sources of NIST's Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) and absolute radiometric traceability from silicon trap radiometers.