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On-Orbit Absolute Calibration of the Global Precipitation Measurement Microwave Imager

On-Orbit Absolute Calibration of the Global Precipitation Measurement Microwave Imager The Global Precipitation Measurement (GPM) Core Observatory was launched on 27 February 2014. One of the principal instruments on the spacecraft is the GPM Microwave Imager (GMI). This paper describes the absolute calibration of the GMI antenna temperature ( T A ) and the earth brightness temperature ( T B ). The deep-space observations taken on 20 May 2014, supplemented by nadir-viewing data, are used for the T A calibration. Data from two backlobe maneuvers are used to determine the primary reflector’s cold-space spillover, which is required to convert the T A into T B . The calibrated GMI observations are compared to predictions from an ocean radiative transfer model (RTM) using collocated WindSat ocean retrievals as input. The mean difference when averaged globally over 13 months does not exceed 0.1 K for any of the nine channels from 11 to 89 GHz. The RTM comparisons also show that there are no significant solar intrusion errors in the GMI hot load. The absolute accuracy of the GMI instrument is defined as the average ocean-viewing error of the measured T A or T B relative to the true T A or T B . Based on the analyses herein, the GMI absolute accuracy for T A is estimated to be about 0.1 K rms over all channels and 0.25 K rms over all channels for T B . http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Atmospheric and Oceanic Technology American Meteorological Society

On-Orbit Absolute Calibration of the Global Precipitation Measurement Microwave Imager

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Publisher
American Meteorological Society
Copyright
Copyright © 2015 American Meteorological Society
ISSN
0739-0572
eISSN
1520-0426
DOI
10.1175/JTECH-D-15-0212.1
Publisher site
See Article on Publisher Site

Abstract

The Global Precipitation Measurement (GPM) Core Observatory was launched on 27 February 2014. One of the principal instruments on the spacecraft is the GPM Microwave Imager (GMI). This paper describes the absolute calibration of the GMI antenna temperature ( T A ) and the earth brightness temperature ( T B ). The deep-space observations taken on 20 May 2014, supplemented by nadir-viewing data, are used for the T A calibration. Data from two backlobe maneuvers are used to determine the primary reflector’s cold-space spillover, which is required to convert the T A into T B . The calibrated GMI observations are compared to predictions from an ocean radiative transfer model (RTM) using collocated WindSat ocean retrievals as input. The mean difference when averaged globally over 13 months does not exceed 0.1 K for any of the nine channels from 11 to 89 GHz. The RTM comparisons also show that there are no significant solar intrusion errors in the GMI hot load. The absolute accuracy of the GMI instrument is defined as the average ocean-viewing error of the measured T A or T B relative to the true T A or T B . Based on the analyses herein, the GMI absolute accuracy for T A is estimated to be about 0.1 K rms over all channels and 0.25 K rms over all channels for T B .

Journal

Journal of Atmospheric and Oceanic TechnologyAmerican Meteorological Society

Published: Oct 20, 2015

References