1212 NPP-CrIS Spectral Gap Channels Prediction and Validation

Wednesday, 10 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Hui Xu, Univ. of Maryland, College Park, MD; and Y. Chen, L. Wang, and C. Cao

CrIS (Cross-track Infrared Sounder) is a hyperspectral infrared sounder mainly for providing atmospheric temperature and moisture profiles to improve weather forecast. It is a Michelson interferometer with 2211 (Full Resolution) channels over three wavelength ranges: long-wave infrared (650-1095 cm-1), middle-wave infrared (1210-1750 cm-1), and short-wave infrared (2155-2550 cm-1). Due to its excellent performance, CrIS radiance is also used as an infrared reference to check calibration accuracy of AVHRR/ABI on GOES, VIIRS on NPP, AHI on HIMAWARI, and other imagers under the GSICS (Global Space-based Inter-Calibration System) framework. However, there are spectral gaps among CrIS three bands, which may impact the capability and comparison accuracy of inter-comparison between CrIS and other instruments.
To fill up the spectra gap, this paper describes a new method to predict the CrIS unmeasured channels based on a ‘Full-CrIS’ (650-2750 cm-1 with 0.625 cm-1 resolution) spectrum derived from IASI (Infrared Atmospheric Sounding Interferometer) observation. We first build a large ‘Full-CrIS’ spectra training dataset based on the spectra selected from different seasons to make sure the data represent different atmospheric and surface conditions. Then, a Multi-Regression method is developed to derive the prediction coefficient matrix between CrIS measured and gap channel spectrum. Finally, the predicted CrIS gap channel radiances are compared with other hyper-spectral infared sounders (such as AIRS and IASI) based on the SNO (Simultaneous Nadir Overpass) events to check their accuracy.
The comparison results demonstrate that the CrIS gap channel radiances can be successfully predicted with high accuracy for the inter-comparison purpose by using the measured CrIS spectral information. The inter-comparison results with other broadband instruments also suggest that the predicted gap channel radiances are generally acceptable and can be used in GSICS in the future.
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