Abstract
The atmospheric infrared sounder (AIRS) science team version-6 AIRS/advanced microwave sounding unit (AMSU) retrieval algorithm is now operational at the Goddard Data and Information Services Center (DISC). AIRS version-6 level-2 products are generated near real time at the Goddard DISC and all level-2 and level-3 products are available starting from September 2002. Some of the significant improvements in retrieval methodology contained in the version-6 retrieval algorithm compared to that previously used in version-5 are described. In particular, the AIRS science team made major improvements with regard to the algorithms used to (1) derive surface skin temperature and surface spectral emissivity; (2) generate the initial state used to start the cloud clearing and retrieval procedures; and (3) derive error estimates and use them for quality control. Significant improvements have also been made in the generation of cloud parameters. In addition to the basic AIRS/AMSU mode, version-6 also operates in an AIRS only (AO) mode, which produces results almost as good as those of the full AIRS/AMSU mode. The improvements of some AIRS version-6 and version-6 AO products compared to those obtained using version-5 are also demonstrated.
Highlights
The atmospheric infrared sounder (AIRS) science team version-6 retrieval algorithm, operational at the Goddard Data and Information Services Center (DISC), contains many significant improvements compared to the previously operational AIRS science team version-5 retrieval algorithm
This was made possible because the AIRS version-5 radiative transfer algorithm (RTA) included the important work of DeSouza-Machado et al.,[4] which accurately accounts for effects of nonlocal thermodynamic equilibrium on shortwave CO2 band radiances during the day
AIRS/advanced microwave sounding unit (AMSU) observations are being processed near real time at the Goddard DISC using both the AIRS science team version-6 retrieval algorithm as well as the AIRS only processing system version-6 AO, which does not use AMSU observations in any way
Summary
Each retrieved quantity X in version-5 and version-6 has an associated error estimate δX. A major advancement in version-5 was the development of a methodology to generate accurate empirical error estimates for a number of geophysical parameters and to use thresholds of these error estimates for quality control (QC) purposes. Version-4 (Ref. 2) used threshold values of 12 internal tests for the purpose of generating QC flags for different geophysical parameters. Version-5 (Ref. 3) used the case-by-case values of these 12 internal tests, as well as values of four additional tests, as predictors to generate empirical case-by-case error estimates δX for select geophysical parameters X. Version-6 uses a methodology analogous to that used in version[5] to generate empirical error estimates δX, with some modifications resulting from changes in the steps used in the version-6 retrieval system as compared to those used in version-5.
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