Formulation and validation of simulated data for the Atmospheric Infrared Sounder (AIRS)

AbstructModels for synthesizing radiance measurements by the Atmospheric Infrared Sounder (AIRS) are described. Synthetics radiances have been generated for developing and testing data processing algorithms. The radiances are calculated from geophysical states derived from weather forecasts and climatology using the AIRS rapid transmission algorithms. The data contains horizontal variability at the spatial resolution of AIRS from the surface and cloud fields. This is needed to test retrieval algorithms under partially cloudy conditions. The surface variability is added using vegetation and IGBP surface type maps, while cloud variability is added randomly. The radiances are spectrally averaged to create High Resolution Infrared Sounder (HIRS) data and this is compared with actual HIRSZ data on the NOAA 14 satellite. The data are in agreement to 1-4 K, but the simulated data under represent high altitude equatorial cirrus clouds and have too much local variability. They agree in the mean to within 1-4 K and global standard deviation agree to better than 2 K. Simulated data have been a valuable tool for developing retrieval algorithms and studying error characteristics and will continue to do so after launch.