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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 11, 971-995, 2018
https://doi.org/10.5194/amt-11-971-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
19 Feb 2018
Single-footprint retrievals of temperature, water vapor and cloud properties from AIRS
Fredrick W. Irion1, Brian H. Kahn1, Mathias M. Schreier1, Eric J. Fetzer1, Evan Fishbein1, Dejian Fu1, Peter Kalmus1, R. Chris Wilson2, Sun Wong1, and Qing Yue1 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91106, USA
2Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA 90095, USA
Abstract. Single-footprint Atmospheric Infrared Sounder spectra are used in an optimal estimation-based algorithm (AIRS-OE) for simultaneous retrieval of atmospheric temperature, water vapor, surface temperature, cloud-top temperature, effective cloud optical depth and effective cloud particle radius. In a departure from currently operational AIRS retrievals (AIRS V6), cloud scattering and absorption are in the radiative transfer forward model and AIRS single-footprint thermal infrared data are used directly rather than cloud-cleared spectra (which are calculated using nine adjacent AIRS infrared footprints). Coincident MODIS cloud data are used for cloud a priori data. Using single-footprint spectra improves the horizontal resolution of the AIRS retrieval from  ∼  45 to  ∼  13.5 km at nadir, but as microwave data are not used, the retrieval is not made at altitudes below thick clouds. An outline of the AIRS-OE retrieval procedure and information content analysis is presented. Initial comparisons of AIRS-OE to AIRS V6 results show increased horizontal detail in the water vapor and relative humidity fields in the free troposphere above the clouds. Initial comparisons of temperature, water vapor and relative humidity profiles with coincident radiosondes show good agreement. Future improvements to the retrieval algorithm, and to the forward model in particular, are discussed.

Citation: Irion, F. W., Kahn, B. H., Schreier, M. M., Fetzer, E. J., Fishbein, E., Fu, D., Kalmus, P., Wilson, R. C., Wong, S., and Yue, Q.: Single-footprint retrievals of temperature, water vapor and cloud properties from AIRS, Atmos. Meas. Tech., 11, 971-995, https://doi.org/10.5194/amt-11-971-2018, 2018.
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Short summary
We describe a new algorithm for the Atmospheric Infrared Sounder (AIRS) that uses its thermal infrared spectra directly rather than using “cloud-clearing.” By additionally modelling clouds within an AIRS field-of-view, we retrieve temperature and water vapor profiles on the AIRS ~13.5 km horizontal footprint (at nadir) rather than the ~45 km footprint of cloud-cleared spectra. Initial validation is presented, and avenues for future development are discussed.
We describe a new algorithm for the Atmospheric Infrared Sounder (AIRS) that uses its thermal...
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