Recalibrating AMSU-A observations on NOAA-16

The Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit (AMSU) onboard NOAA polar orbiting satellites provide global temperature profile observations for both weather and climate applications. However, climate applications require these observations to be well-intercalibrated to reduce satellite transition errors in satellite product retrievals and modeling reanalysis practice. It was found that NOAA-16 AMSU-A channels suffered a long-term bias-drift relative to the same AMSU observations but from other NOAA and NASA satellites. This bias-drift may result in false climate trend when NOAA-16 is used in the construction of atmospheric temperature climate data records (CDRs). In this study, we analyze the root cause of this bias-drift and develop a technique to correct it. We found that the NOAA-16 raw counts data have a long-term decrease, which cause its brightness temperature to slowly decrease due to inadequate pre-launch calibration. Based on this observation, we modify the root-level calibration to account for the raw counts decrease. After the correction, the bias-drift between NOAA-16 and other satellites such as NOAA-15 was reduced to near zero and the NOAA-16 observations can now be safely used in the long-term atmospheric temperature CDRs. We will present the merged MSU/AMSU time series and trend developed at NESDIS/Center for Satellite Applications and Research (STAR) when the MSU and AMSU observations from all NOAA polar orbiting satellites are used.