Radiometric Accuracy and Stability of the Atmospheric Infrared Sounder (AIRS) on Aqua

Abstract:

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002. AIRS acquires hyperspectral infrared radiances in 2378 channels ranging in wavelength from 3.7-15.4 um with spectral resolution of better than 1200, and spatial resolution of 13.5 km with global daily coverage. The AIRS was designed to measure temperature and water vapor profiles for improvement in weather forecast and improved parameterization of climate processes. Currently the AIRS Level 1B Radiance Products are assimilated by NWP centers worldwide and have shown considerable forecast improvement. AIRS L1 and L2 products are widely used for studying critical climate processes related to water vapor feedback, atmospheric transport and cloud properties. AIRS trace gas products include ozone profiles, carbon monoxide, and the first global maps of mid-tropospheric carbon dioxide. The global daily coverage of AIRS allows scientists to follow the transport of these gases to aid in validation of chemical/weather transport models.

The AIRS radiances are calibrated using a uniform on-board blackbody and full aperture space view and are recognized to have stability and accuracy for most channels of better than 200 mK for most scene types. The AIRS pre-flight tests that impact the radiometric calibration include a full system radiometric response (linearity), polarization response, and response vs scan angle (RVS). We compare the AIRS instrument radiometric calibration coefficients from the pre-flight polarization measurements, the response vs scan (RVS) angle tests as well as the linearity tests, and lunar roll test taken in orbit that allowed the AIRS to view deep space. New methods are employed using MODIS to correct the AIRS radiances in non-uniform scenes for channels with non-uniform spatial response, and PC reconstruction to evaluate the accuracy of the calibration in orbit that can ultimately be used to improve the calibration. The data and method for deriving the coefficients and evaluating the calibration is discussed and the stability and accuracy of the radiometric calibration compared pre-launch with current estimates in orbit.