AIRS Level 1 Data Products

Calibrated and geolocated radiances

The Level 1B (L1B) data product contains measurements of the upwelling radiation from the Earth's surface and atmosphere. There are separate data products for the geolocated and calibrated infrared (IR L1B algorithm), microwave (AMSU and HSB algorithm) and visible/near-infrared radiances (Vis/NIR algorithm). All L1B data are presented at the instrument native spatial resolution along with Quality Assessment (QA) data. The data are presented in 6-minute data granules, 240 granules each day.

The AIRS infrared Level 1B data product contains the radiances of all 2378 channels. The 2378 channel radiances are calibrated using the Onboard Blackbody Calibrator, which is actively temperature controlled to 308 K. The channel frequencies, which are determined using the upwelling radiances and reported in the product for each granule, vary slowly (by 1% of the SRF width) with time, season, orbit phase and ascending node of the orbit (IR L1B algorithm).

The AIRS Level 1C (L1C) data product is derived from the infrared L1B product. It provides 2645 channels on a fixed frequency grid, which provides gap-free and overlap-free spectral coverage. The 2378 L1B channels are radiometrically shifted from the “as measured by L1B” frequencies to the fixed grid. L1C product also mitigates co-registration errors seen at module boundaries in highly non-homogeneous scenes. Channels with noise larger than NEDT of 1 K and channels in gaps are filled using principle component reconstruction (L1C algorithm).

The Aqua AIRS Calibration Subset (AIRS CalSub) data product contains the data necessary to facilitate the evaluation of the AIRS L1 data (two daily files, typically 150 MB in size). In addition to the data necessary to evaluate the absolute radiometric and spectral accuracy, CalSub also includes data from extreme cloudy, hot and cold conditions and 40,000 uniformly distributed random samples each day. These data facilitate the evaluation of trends and their potential significance relative to climate trends. Parallel CalSub products for SNPP CrIS NSR L1 facilitate cross-instrument comparisons.

The AIRS design ensures that the accuracy of the L1B and L1C products will not change when the ascending node and altitude of the EOS Aqua orbit is allowed to drift.