Development of a calibrated optical gas chamber for the ground testing of a satellite-borne detector.

This work presents the fabrication of a gas chamber that will be a part of an experimental setup to calibrate a satellite-based detector. The gas chamber is cubic, with six aluminum plates, each 10 mm thick. The dimensions of the base plate are 560×410mm2, followed by the side plates having dimensions of 410×120mm2, and front and back plates having dimensions of 560×120mm2. Nine concave mirrors (M1-M9) of diameter 25.4 mm have been arranged to provide a path length of 344 cm. Mirrors M1 and M9 were inclined by 5∘ to optimize beam confinement and reflection uniformity throughout the chamber. The optical performance of the setup has been validated using a photodetector and a satellite-based detector. For the photodetector, the incident intensity was estimated by accounting for losses due to the mirrors' reflectivity and the optical components' transmission. This intensity has been converted into a voltage output using the detector's responsivity equations. The theoretically calculated voltage was compared with experimentally measured voltage to determine the chamber's efficiency and alignment precision. The relative error between the theoretically estimated value and the experimental result was 11%-12%. For the satellite detector, the photon flux incident on the detector plane (512×640 array) was computed and compared with the simulated photon count. The relative error between the theoretical and experimental photon fluxes for different filters across the satellite's detector is 15% for CO2, 12% for CH4, 10.6% for N2O, 13.5% for H2O-B1, 13.7% for H2O-B2, 13% for wide band, and 15.4% for reference filter. The close agreement between theoretical and experimental values confirms the chamber's suitability for calibrating and validating a space-applied detector. The major achievement of this work is a compact, cost-effective, and high-precision optical gas chamber, which enables controlled, repeatable ground calibration of satellite-borne detectors under simulated atmospheric conditions.