The Atmospheric Infrared Sounder (AIRS) is a grating spectrometer (R = 1200) aboard the second Earth Observing System (EOS) polar-orbiting platform, EOS Aqua. AIRS/Aqua Level-1C calibration subset including clear cases, special calibration sites, random nadir spots, and high clouds. Infrared temperature sounders generate a large amount of Level-1B spectral data. For example, the AIRS instrument with 2378 channels, its visible light component and AMSU with 15 channels create 3x240 files each day, for a total of over 500 MB of data.
The purpose of the Calibration Data Subsets is extract key information from these data into a few daily files to:
1. Facilitate a quick evaluation of the absolute calibration of the instruments.
2. Facilitate an assessment of the instrument performance under clear, cloudy, and extreme hot and cold conditions.
3. Facilitate the evaluation of instrument trends and their significance relative to climate trends.
4. Facilitate the comparison of AIRS with CrIS using their equivalent data subsets.
The output files are constructed from Level-1B or Level-1C IR and MW brightness or antenna temperatures. Each file contains selected observations taken from a nominal 24-hour period. The “summary” product includes a large set of cases of interest, including all identified spectra that match selection criteria detailed below for clear, special cloud classes, etc. These amount to about 10% of all spectra. But for each selected case only brightness temperatures (BTs) for selected key channels are saved.