Recalibration of the NOAA microwave sounding unit

The microwave sounding unit (MSU) prelaunch thermal-vacuum chamber test dat a for eight MSU flight models that flew on TIROS-N, NOAA 7 through NOAA 12, and NOAA 14 were reanalyzed using an improved calibration algorithm, origi nally designed for the advanced microwave sounding unit-a (AMSU-A) operatio ns. The new calibration algorithm can automatically adjust for any channel gain shift in operation. Adoption of this calibration algorithm as the MSU calibration procedure in the recalibration project will make the data sets From the MSU and the AMSU-A more consistent. This will be useful for future blending of the climate trends generated from the MSU and AMSU-A data. A s ingle nonlinearity parameter u, which appears in the new calibration algori thm, was obtained for each channel from analysis of the prelaunch calibrati on test data. A software package for implementing this new calibration algo rithm was developed and applied to calculate the MSU time series for improv ement of the accuracy of the climate record. Sample calculations of MSU ant enna temperatures with the new calibration algorithm were made for two sate llites and are compared with similar results obtained from the old MSU cali bration algorithm. Significant differences are observed, and strong evidenc e indicates that the new calibration procedure will provide a more accurate quantification of climate trends.