A detector-based absolute radiometric calibration simulation for a climate-quality imaging spectrometer

The HyperSpectral Imager for Climate Science (HySICS) is the core instrument of the CLARREO Pathfinder (CPF) mission and scheduled to be launched to the International Space Station (ISS) in 2023. HySICS is an Offner-Chrisp imaging spectrometer designed to meet an unprecedented radiometric uncertainty requirement of 0.3% (k=1) across its 350-2300 nm spectral range. The requirement represents a need for significant improvement over the radiometric calibration (RadCal) of existing space-borne spectrometers. The strategy to demonstrate that HySICS achieves this level of uncertainty includes an Independent Calibration (IndCal) using a pre-launch, detector-based RadCal relying on a tunable laser source. The system planned for the IndCal is the Goddard Laser for Absolute Measurement of Radiance (GLAMR) that has been developed at NASA's Goddard Space Flight Center and used recently in the absolute radiometric calibration of several multi-spectral instruments. GLAMR data from a calibration demonstration system developed for the CLARREO mission have been combined with HySICS characterization data to develop an imaging spectrometer model that simulates HySICS' behavior. The goal of the HySICS instrument and GLAMR model is to prepare for GLAMR testing of HySICS, optimize the test configuration, and verify the RadCal error budget. A Monte-Carlo simulation of the GLAMR RadCal based on the model is conducted to predict the detectors' outputs at miscellaneous testing parameters. The main application of the simulation is a sensitivity study through the tuning of these parameters to identify the calibration error sources and determine quality metrics that can define the need for repeat HySICS measurements. The HySICS instrument model developed will be maintained and improved to support the CPF IndCal.