Methane retrieval from Atmospheric Infrared Sounder using EOF-based regression algorithm and its validation
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This paper presents a rapid regression algorithm for the retrieval of methane (CH4) profile from Atmospheric Infrared Sounder (AIRS) based on empirical orthogonal functions (EOF) and its validation. This algorithm was trained using the simulated radiance from an assemble of atmospheric profiles and can be utilized to derive the CH4 profile rapidly with the input of the AIRS cloud-clear radiance. Validation using hundreds of aircraft profiles demonstrates that the root mean square error (RMSE) is about 1.5 % in the AIRS sensitive region of 359–596 hPa, which is smaller than AIRS-V5 product (except in high latitudes). Comparison with the ground-based solar Fourier transform spectrometry observations showed that the RMSE of the retrieved CH4 total column amount is less than 3 %. This EOF-based regression method can be easily applied to other thermal infrared sounders for deriving CH4 and some other gases, and the derived profiles can be used as the first guess for further physical retrieval.
KeywordsEOF Methane AIRS Remote sensing Regression
This work was supported by the Strategic Priority Research Program – Climate Change: Carbon Budget and Relevant Issues of the Chinese Academy of Sciences (XDA05090101) and the Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences (Y1S02000CX). The authors gratefully thank Network for the Detection of Stratospheric Change to provide ground-based FTS measurements. The data of INTEX-A and B used in this publication were obtained from Aura Validation Data Center (AVDC) (http://avdc.gsfc.nasa.gov/index.php) and the aircraft measurements of INTEX-A were carried out by Donald R. Blake of Department of Chemistry, University of California, Irvine; and airborne CH4 data from INTEX-B and ARCTAS were provided by Glen Sachse and Glenn Diskin of NASA Langley. ARCTAS data were downloaded from (http://ftp-air.larc.nasa.gov/pub/ARCTAS/). The CH4 data of START08 aircraft measurements were carried out by Dale Hurst and Jim Elkins of NOAA/ESRL/GMD. The CH4 data of HIPPO aircraft measurements were carried out by S.C. Wofsy, HIPPO science team and cooperating modelers and satellite team.
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