Evaluation and validation of a vacuum-compatible, spectrally tunable, flat panel uniform source for testing large aperture earth observation systems

NASA GSFC, in conjunction with Labsphere Inc. and Genesis Engineering Solutions Inc., has performed tests and characterizations of the Flat Panel Illuminator 2 (FPI-2) system in both ambient and thermal vacuum environments to validate and verify its performance prior to use with the Joint Polar Satellite System-3 (JPSS-3) Visible Infrared Imaging Radiometer Suite (VIIRS) and JPSS-4 VIIRS instruments during spacecraft level testing. The system is an innovative, vacuum compatible, calibrated spectroradiometric illumination source and successor to the FPI-1. Designed to provide a large, uniform, active output area, the FPI-2 maintains a small form factor allowing it to serve as an in-vacuum calibration target for the VIIRS instrument’s optical bands during pre-launch testing. The system utilizes an in-vacuum light head with liquid-cooled hybrid quartz-tungsten (QT) and light emitting diode (LED) sources and an optimized integration chamber. Temperature control, radiometric control, and radiometric monitoring are provided by non-vacuum compatible hardware: a chiller unit, fiber coupled spectroradiometers, custom power supplies and software. The test campaign at GSFC builds on evaluations performed at Labsphere, Inc to validate key performance requirements passed down from the VIIRS and JPSS programs including radiometric output and spatial uniformity in both ambient and vacuum environments. The demonstrated performance and adaptability of the system make it capable of meeting the needs of many other instruments/missions requiring this type of test/calibration. The system will soon be compared side-by-side with the FPI-1 system and serve as the radiometric target for performance tests of the JPSS-3 and JPSS-4 VIIRS instruments.