Truths cross-calibration uncertainty tool

This paper describes a set of tools, algorithms and methodologies that have been developed and used in order to estimate the radiometric uncertainty achievable for a Sentinel 2/3 like sensor through in-flight cross-calibration using a well-calibrated hyperspectral SI traceable reference sensor such as the proposed TRUTHS (Traceable Radiometry Underpinning Terrestrial- and Helio- Studies) mission. This first study considers the criticality of the instrumental and observational characteristics in a fully iterative manner and uses the Libya-4 Pseudo Invariant Calibration Site (PICS) as a demonstration. The main uncertainty contributions have been studied: spectral response, reflectance heterogeneity, sun angular effect and aerosol (spatial and temporal) effects. The tool contributes to optimizing the design of TRUTHS; but will find immediate use in support of existing sensor-to-sensor cross-calibration activities being carried out under the auspices of Committee on Earth Observation Satellites (CEOS).