Post-Launch Assessment of the METOP-A AMSU-A Performance

After successful launch of the Advanced Microwave Sounding Unit-A (AMSU-A) onboard the Meteorological Operations Platform A (METOP-A), a systematic On-orbit Verification (OV) with on-orbit AMSU-A data was performed. Some of the OV results are reported here. Scan-by-scan examination of the radiometric calibration counts is employed to confirm normal functioning of the instrument and to detect any anomalous evens, such as lunar contamination (LC) in space counts, which are detected and corrected using an algorithm for LC correction in AMSU-A data. This algorithm provides a practical approach for scan-by-scan LC correction in AMSU-A data and improves the accuracy of operational calibration of AMSU-A data. Long-term trends of the space and warm calibration counts, channel gains, housekeeping sensors, and NEDeltaT are monitored. Monthly mean angular distributions of ocean brightness temperatures (T_B) from METOP-A and NOAA-18 over the tropical ocean region of 20degS-20degN are obtained and modeled to demonstrate that the ocean can be used as a cold reference calibration target. The establishment of a natural Earth calibration target is important for calibration of microwave radiometers. The measured ocean T_B values from the four satellites provide eight measurements across the diurnal time for studying the diurnal variation of ocean brightness temperatures which show a pattern of daytime cooling and nighttime warming.