The Atmospheric Infrared Sounder (AIRS) is a facility instrument aboard the second Earth Observing System (EOS) polar-orbiting platform, EOS Aqua. In combination with the Advanced Microwave Sounding Unit (AMSU) and the Humidity Sounder for Brazil (HSB), AIRS constitutes an innovative atmospheric sounding group of visible, infrared, and microwave sensors.  AIRS data will be generated continuously. Global coverage will be obtained twice daily (day and night) on a 1:30pm sun synchronous orbit from a 705-km altitude.
                                                      
                                                      The AMSU-A level 1B data set contains AMSU-A calibrated and geolocated brightness temperatures in degrees Kelvin. This data set is generated from AMSU-A Level 1A digital numbers (DN), including 15 microwave channels in the 50 - 90 GHz and 23 - 32 GHz regions of the spectrum. A day&apos;s worth of data is divided into 240 scenes each of 6 minute duration. An AMSU-A scene contains 30 cross-track footprints in each of 45 along-track scanlines, for a total of 45 x 30 = 1350 footprints per scene. The AMSU-A is co-aligned with the AIRS instrument onboard the Aqua platform so that successive blocks of 3 x 3 AIRS footprints are contained within the AMSU-A footprint.
                                                      
                                                      AMSU-A is primarily a temperature sounder that provides atmospheric information in the presence of clouds, which can be used to correct the AIRS infrared measurements for the effects of clouds. This is possible because non-precipitating clouds are for the most part transparent to microwave radiation, in contrast to visible and infrared radiation which are strongly scattered and absorbed by clouds. Combined with simultaneous measurements from the AIRS and HSB instruments, the calibrated AMSU-A brightness temperatures will also be used to initialize the surface temperature and atmospheric temperature profile required for the retrieval of the final AIRS geophysical products. 
                                                      
                                                      (The Shortname for this product is AIRABRAD_NRT).

                                                      Coverage: Global, Twice Daily (Daytime and Nighttime)
                                                      Resolution: 40.5 km IFOV at nadir
                                                      Spectral Range:
                                                      AMSU-A1: 13 channels from 50 - 90 GHz
                                                      AMSU-A2: 2 channels from 23 - 32 GHz