Abstract
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) is a conically-scanning, 13 channel, total power microwave radiometer. The radiometer employs channels at frequencies of 10.65, 18.7, 23.8, 36.64, 89, 166, 183.31±3, and 183.31±7 GHz. The instrument operates in concert with the GPM Dual-Frequency Precipitation Radar (DPR) to measure global precipitation products for use in weather monitoring and forecasting. The GMI design for on-orbit calibration includes warm load and cold sky design features that mitigate many of the radiometric calibration issues observed on historical microwave radiometers. The GPM spacecraft was launched on February 27, 2014. During the first year of on-orbit operations, calibration and validation activities demonstrated the accuracy and stability of the GMI calibration.
The GMI radiometer was designed, built, and tested by Ball Aerospace & Technologies Corp. After launch, on-orbit data were processed and analyzed to determine the performance of key radiometric parameters. Extensive calibration and validation of the lower frequency channels (36 GHz and below) showed that the instrument meets radiometric performance requirements, offering stable, accurate brightness temperatures for use in the retrieval of geophysical products.
This paper evaluates the calibration performance of the high frequency channels at 89 GHz and above. We compare the GMI brightness temperatures with similar channels from the concurrent Advanced Technology Microwave Sounder (ATMS) and Microwave Humidity Sounder (MHS) instruments. ATMS flies onboard the NPP-Suomi spacecraft, while MHS is presently flying on two NOAA and two MetOp spacecraft. GPM’s 65 degree inclination orbit offers numerous colocations with the polar-orbiting ATMS and MHS instruments every orbit. We compare the calibrated brightness temperatures between the common channels and look for trends spatially, temporally, and as a function of orbital and geophysical parameters. Cross-calibration performance is reported with an evaluation of potential sources of observed differences.
On-orbit Cross-Calibration of GMI High Frequency Channel Brightness Temperatures
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) is a conically-scanning, 13 channel, total power microwave radiometer. The radiometer employs channels at frequencies of 10.65, 18.7, 23.8, 36.64, 89, 166, 183.31±3, and 183.31±7 GHz. The instrument operates in concert with the GPM Dual-Frequency Precipitation Radar (DPR) to measure global precipitation products for use in weather monitoring and forecasting. The GMI design for on-orbit calibration includes warm load and cold sky design features that mitigate many of the radiometric calibration issues observed on historical microwave radiometers. The GPM spacecraft was launched on February 27, 2014. During the first year of on-orbit operations, calibration and validation activities demonstrated the accuracy and stability of the GMI calibration.
The GMI radiometer was designed, built, and tested by Ball Aerospace & Technologies Corp. After launch, on-orbit data were processed and analyzed to determine the performance of key radiometric parameters. Extensive calibration and validation of the lower frequency channels (36 GHz and below) showed that the instrument meets radiometric performance requirements, offering stable, accurate brightness temperatures for use in the retrieval of geophysical products.
This paper evaluates the calibration performance of the high frequency channels at 89 GHz and above. We compare the GMI brightness temperatures with similar channels from the concurrent Advanced Technology Microwave Sounder (ATMS) and Microwave Humidity Sounder (MHS) instruments. ATMS flies onboard the NPP-Suomi spacecraft, while MHS is presently flying on two NOAA and two MetOp spacecraft. GPM’s 65 degree inclination orbit offers numerous colocations with the polar-orbiting ATMS and MHS instruments every orbit. We compare the calibrated brightness temperatures between the common channels and look for trends spatially, temporally, and as a function of orbital and geophysical parameters. Cross-calibration performance is reported with an evaluation of potential sources of observed differences.