The Angular Correction Algorithm for the Intercalibration of Satellite Instruments Using CLARREO Pathfinder as a Reference

The Climate Absolute Radiance and Refractivity (CLARREO) Pathfinder (CPF) mission will take Système Internationale (SI)-traceable spectral reflectance measurements of Earth at an unprecedented accuracy of 0.3% (
${k}$
= 1). CPF will also take measurements to support intercalibration of other satellite-based sensors. To achieve the desired intercalibration methodology uncertainty of 0.3% (
$k$
= 1), the CPF intercalibration measurements need to closely match those from target sensors in time, space, angles, and wavelength. This article introduces an innovative angular correction method to significantly reduce errors due to angular mismatches between CPF and target sensor measurements. The method leverages the spectral correlations among the reflected solar (RS) radiances from the same surface target at two adjacent angles. Our studies have shown that the spectral radiance or reflectance difference measured at angles slightly deviating from the CPF observation angles can be accurately predicted based on the hyperspectral CPF measurements. The method will serve as part of the operational algorithms to support the core mission goal of conducting intercalibration analysis with measurements from the shortwave channel of the Clouds and the Earth’s Radiance Energy System (CERES) and the reflective solar bands of the Visible Infrared Imaging Radiometer Suite (VIIRS); however, it can also be extended for other reference-target intercalibration applications.