The Goddard Earth Sciences Data and Information Services Center (GES DISC), in collaboration with the Atmospheric Infrared Sounder (AIRS) data team at the NASA Jet Propulsion Laboratory (JPL), is announcing the availability of the AIRS Level 1C spectrum data product (AIRICRAD). See the links at the bottom of this article for information on how to access this data product.
The AIRS Level 1C (AIRICRAD) Version 6 product is derived from Version 5 Level 1B radiances with corrections for noisy channels, removal of spectral overlap channels, and other instrument artifacts. Unlike the L1B radiances, which are optimized for users who are interested in specific channels, the L1C is optimized for applications which require spectra. As such the L1C is suitable for Principal Component analysis and comparative studies with IR measurements from other instruments with different spectral sampling and/or spectral resolution, such as the Moderate Resolution Imaging Spectroradiometer (MODIS), the Cross Track Infrared Sounder (CrIS), and the Infrared Atmospheric Sounding Interferometer (IASI). Users are advised to review the Level 1C User Guide and the Level 1C ATBD to assess whether the L1C product is more suitable for their needs than the L1B product.
Figure 1a shows an AIRS Version 5 Level 1B spectrum (black) superimposed on an AIRS Version 6 Level 1C spectrum (red). Figure 1b shows this more clearly for the 8.5-11 micron region, which includes the broad Ozone band. A higher resolution image is available here. The Level 1C spectrum is visible (in red) where corrections have been made or gaps were filled. Noisy channels and spectral gaps in the L1B are filled with information from the 2378 AIRS L1B channels, including some weak water lines. The resulting Level 1C product has 2645 spectral channels, with monotonically increasing spectral frequencies.
The Level 1C product includes three new variables to describe the spectra. These variables allow the user to identify which Level 1C channels have been copied directly from the L1B and which have been synthesized from the L1B and why. The variable names are L1cProc, L1cSynthReason, and Inhomo850. Scene inhomogeneity near the edges of deep convective clouds creates a radiometric offset in some channels. The variable Inhomo850 provides the value of the offset (as a brightness temperature step measured in degrees K at 850 cm-1). For most scenes Inhomo850 is less than 1K.
Only the most-recent 30 days of AIRS L1C spectrum data files will be stored and made available by the GES DISC. The data are available by several different methods listed on the AIRS Level 1C Data Access page.
The Level 1C product is described in more detail in the Level 1C User Guide and the Level 1C ATBD. More general information about the AIRS instrument can be found on the AIRS documentation page.
Questions or comments? Email the NASA GES DISC Help Desk: firstname.lastname@example.org,