Characterization and verification of ACAM slit functions for trace-gas retrievals during the 2011 DISCOVER-AQ flight campaign

摘要

The Airborne Compact Atmospheric Mapper (ACAM), anultraviolet/visible/near-infrared spectrometer, has been flown on board theNASA UC-12 aircraft during the Deriving Information on SurfaceConditions from Column and Vertically Resolved Observations Relevant to AirQuality (DISCOVER-AQ) campaigns to provide remote sensing observations of troposphericand boundary-layer pollutants from its radiance measurements. To assure thetrace-gas retrieval from ACAM measurements we perform detailedcharacterization and verification of ACAM slit functions. The wavelengthsand slit functions of ACAM measurements are characterized for the air-quality channel (~304–500 nm) through cross-correlation witha high-resolution solar irradiance reference spectrum after necessarilyaccounting for atmospheric gas absorption and the ring effect in thecalibration process. The derived slit functions, assuming a hybridcombination of asymmetric Gaussian and top-hat slit functions, agree verywell with the laboratory-measured slit functions. Comparisons of trace-gasretrievals between using derived and measured slit functions demonstratethat the cross-correlation technique can be reliably used to characterizeslit functions for trace-gas retrievals.