Updates to the AIRS level 1B and level 1C data products in version 8

Abstract

The Atmospheric Infrared Sounder (AIRS) was launched on May 4, 2002, onboard the Earth Observing System (EOS) Aqua spacecraft. AIRS measures the upwelling spectral radiance in infrared from 3.7-15.4 μm in 2378 spectral channels. Radiances are used to retrieve atmospheric temperature and water vapor profiles, as well as concentrations of several trace gases. The Level 1B (L1B) radiance product is produced from measured counts and instrument telemetry, including onboard blackbody temperatures, scan mirror temperatures, and in-orbit views of deep space for the polarization amplitude and phase. The calibration also uses coefficients obtained pre-flight including blackbody emissivity and temperature offset and nonlinearity. Spectral calibration is performed in L1B with frequencies reported, but the frequencies are known to drift throughout the mission by a small amount. The AIRS Level 1C (L1C) product resamples the L1B radiances to a fixed grid for the entire mission and corrects instrument-related artifacts. including bad detectors, to produce a spectrally consistent, gap-filled, and cleaned radiance product. L1C makes it easier to use in scientific investigations or in a geophysical product retrieval (Level 2 data product). Updates to the L1B product in Version 8 (V8) include improved pre-flight calibration coefficients including effective emissivity and nonlinearity, improved polarization correction using in-flight data, and improved frequency calibration reporting. Updates to the L1C product in V8 include dynamic spectral calibration (vs. model), updated channel replacement criteria, and correction for biases seen in module M8 in cold scenes in channels with A side only or B side only detector redundancy. Both L1B and L1C in V8 now output in NetCDF format, improving accessibility and interoperability with modern Earth science and data analysis.