Comprehensive Vicarious Calibration and Characterization of a Small Satellite Constellation Using the Specular Array Radiometric Calibration (SPARC) Method

With a rapidly growing small satellite industry deploying constellations of low cost imaging sensors for academic, commercial, civil, and intelligence applications, the quality and exploitability of data products will play a critical role in maintaining that growth. As a result, absolute intersensor calibration is critical in providing reproducible and accurate measurements over time for delivering image data that is affordable, maximizes information content, and optimizes value added potential. A significant part of keeping the cost down has typically been the elimination of on-board calibration and relying on vicarious calibration methods. Robust techniques are required to ensure that observations from different instruments establish a reliable form of traceability and can be normalized to a common absolute radiometric scale for achieving seamless physics based exploitation. Outlined in this paper is a versatile and effective method for achieving calibration equalization and performance characterization of a constellation of imaging sensors in the solar reflective spectrum. The Specular Array Calibration (SPARC) method, is an adaptable ground based system that uses convex mirrors to create small reference targets revealing radiometric, spatial, spectral, geometric and temporal characteristics of individual sensors for transforming them into a unified earth-monitoring system. Overall, the wide range of SPARC capabilities provides the potential to minimize pre-flight requirements (reduce cost and schedule) by being able to shift more calibration and validation analysis on orbit, completed quickly after launch and continued routinely through the life of each imaging system and duration of the constellation