AMSU-A antenna pattern corrections

A procedure for making antenna pattern corrections to antenna temperatures of the advanced microwave sounding unit-A (AMSU-A) is developed. Antenna efficiencies, fractions of total power over three different solid-angle regions subtended at the satellite by the Earth (plus atmosphere below 20 km), cold space, and the satellite platform, were calculated at 30 Earth views and four possible cold space calibration positions. These calculated results simplify the process for correcting antenna temperature measurements to retrieve the true brightness temperatures from AMSU-A data. Using the antenna pattern data and a profile of atmospheric brightness temperature, a set of antenna pattern corrections was simulated for each channel at the 30 Earth views and four possible cold space calibration positions. The results show that these corrections can add 0.5 to 2.7 K to the antenna temperatures to retrieve the brightness temperatures and that the cold space calibration temperatures may be raised to 2 K above the nominal cold sky temperature of 2.73 K. Antenna pattern 3-dB beamwidths and main-beam efficiencies were also calculated from the antenna pattern data