Assessing calibration stability of the airborne Lunar Spectral Irradiance (air-LUSI) instrument

The airborne Lunar Spectral Irradiance (air-LUSI) instrument performs high-accuracy, SI-traceable measurements of lunar spectral irradiance from the NASA ER-2 aircraft. This study evaluates the in-flight calibration stability of air-LUSI using an onboard LED validation source. Signal behavior across multiple flights is analyzed to assess instrument responsivity and identify potential drift sources. Results demonstrate that instrument responsivity remained stable throughout all flight segments, with the redundant LED monitoring approach proving effective at isolating optical and electronic instabilities from LED source fluctuations. Together, these findings provide diagnostic evidence that ground-based calibration references remain valid during operational lunar measurements, strengthening confidence in the SI-traceability of air-LUSI lunar irradiance data. These findings support the role of air-LUSI in providing fiducial reference measurements toward the development of robust standards for calibration and cross-calibration of satellite sensors using the Moon as a radiometric reference.