The present study describes artificial neural network (ANN) based approach for the retrieval of atmospheric temperature profiles from AMSU-A microwave temperature sounder. The nonlinear relationship between the temperature profiles and satellite brightness temperatures dictates the use of ANN, which is inherently nonlinear in nature. Since latitudinal variation of temperature is dominant one in the Earth’s atmosphere, separate network configurations have been established for different latitudinal belts, namely, tropics, mid-latitudes, and polar regions. Moreover, as surface emissivity in the microwave region of electromagnetic spectrum significantly influences the radiance (or equivalently the brightness temperature) at the satellite altitude, separate algorithms have been developed for land and ocean for training the networks. Temperature profiles from National Center for Environmental Prediction (NCEP) analysis and brightness temperature observations of AMSU-A onboard NOAA-19 for the year 2010 have been used for training of the networks. Further, the algorithm has been tested on the independent dataset comprising several months of 2012 AMSU-A observations. Finally, an error analysis has been performed by comparing retrieved profiles with collocated temperature profiles from NCEP. Errors in the tropical region are found to be less than those in the mid-latitude and polar regions. Also, in each region the errors over ocean are less than the corresponding ones over land. 1. Introduction Numerical weather prediction (NWP) is crucially dependent on proper initialization of NWP models, which effectively boils down to an accurate estimation of the present atmospheric state, a vitally important component of which is the atmospheric temperature profile. Such profiles can be estimated from observations taken by satellite-borne sounders operating in the microwave region of electromagnetic spectrum. The Advanced Microwave Sounding Unit (AMSU) A on board the latest generation of the National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites measures the outgoing radiances from the atmosphere and the Earth surface. With channels in the oxygen absorption band, AMSU-A is designed to retrieve the atmospheric temperature from about 3？hPa (~45？km) down to the Earth’s surface. The AMSU sounding unit operates on board the NOAA satellites since 1998. AMSU-A has 11 channels located close to the oxygen absorption lines below 60？GHz and four window channels at 23.8, 31.4, 50.3, and 89？GHz. The instrument has instantaneous fields of view of 3.3° and
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