Imaging spectrometer stray spectral response: In-flight characterization, correction, and validation

We present a new method for more accurate in-flight calibration and correction of imaging spectrometer spectral response functions. Non-Gaussian tails of spectral response functions can be difficult to characterize in the laboratory, and calibration can shift during deployment. Consequently, in-flight techniques are useful for validating and updating laboratory measurements. Our approach exploits predictable changes in the shape of the oxygen A band across varying surface elevation, with diverse scene content providing numerical leverage to characterize spectral response tails 3-4 orders of magnitude below the peak. We present a correction to recover the nominal response function, and show case studies based on NASA's Next Generation Airborne Visible Infrared Imaging Spectrometer (AVIRIS-NG). Corrected radiances are better conditioned for downstream analysis by sensitive atmospheric codes. We evaluate accuracy using multiple independent standards: simulation studies; consistency with laboratory measurements; elimination of a surface pressure retrieval bias; better alignment of retrieved reflectance with ground reference data; and statistics of over 250 flightlines from a campaign across the Indian Subcontinent showing consistent improvements in atmospheric correction.