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| GPM Microwave Imager | |
|---|---|
| Name | GPM Microwave Imager |
| Mission type | Earth observation |
| Operator | National Aeronautics and Space Administration / Japan Aerospace Exploration Agency |
| Mission duration | Ongoing |
| Launch mass | 180 kg (approx.) |
| Power | ~150 W |
| Orbit | Low Earth orbit |
| Instruments | Radiometer |
| Programme | Global Precipitation Measurement |
GPM Microwave Imager is a conical‑scanning passive microwave radiometer flown as part of the Global Precipitation Measurement constellation operated jointly by National Aeronautics and Space Administration and Japan Aerospace Exploration Agency. The instrument measures microwave radiances emitted and scattered by hydrometeors, surface emission, and atmospheric constituents to estimate precipitation intensity, phase, and structure. Data from the instrument support retrievals used by organizations such as European Space Agency, National Oceanic and Atmospheric Administration, Japan Meteorological Agency, and research groups at institutions like Massachusetts Institute of Technology and University of Colorado Boulder.
The instrument was developed for the GPM Core Observatory, deployed to provide a radiometric reference for constellation intercalibration with satellites including sensors on Fengyun-3, METOP-A, SAC-D Aquarius, and Terra. It operates near the confluence of meteorology and hydrology communities including users from World Meteorological Organization, United Nations Office for Disaster Risk Reduction, and research consortia such as GEWEX. The radiometer contributes to global precipitation products used by agencies like NASA, JAXA, NOAA, and academic centers at Columbia University, University of Maryland, and Scripps Institution of Oceanography.
The radiometer is a multichannel, dual‑polarization passive microwave imager covering frequencies that sample atmospheric scattering and emission signatures at centimeter wavelengths. Its design builds on heritage from instruments such as TRMM Microwave Imager, Special Sensor Microwave/Imager, and Advanced Microwave Scanning Radiometer while incorporating advances from programs at Jet Propulsion Laboratory, NASA Goddard Space Flight Center, and Caltech. The antenna subsystem uses a conical scan geometry to provide broad swath coverage; the cryogenic and thermal control design drew on engineering teams at Ball Aerospace and Northrop Grumman. Channels exploit spectral lines and continuum bands comparable to those used by instruments on Global Change Observation Mission, enabling discrimination of liquid, ice, and mixed precipitation. Onboard electronics were integrated with spacecraft systems provided by Mitsubishi Electric, and calibration targets were developed in collaboration with laboratories at National Institute of Standards and Technology.
Absolute radiometric calibration employs cold references, internal noise sources, and vicarious methods tied to ground sites and shipborne campaigns organized with partners such as Office of Naval Research, Naval Research Laboratory, and international centers including German Aerospace Center and Centre National d'Études Spatiales. Validation campaigns matched radiometer retrievals to in situ observations from networks like GPM Ground Validation, sounding arrays coordinated with NOAA Pacific Marine Environmental Laboratory, disdrometer installations at Colorado State University, and radar measurements from systems such as NEXRAD. Intercalibration procedures referenced standards promulgated by International Telecommunication Union and cross‑compared with instruments on platforms from European Organisation for the Exploitation of Meteorological Satellites.
Level 1 radiances are generated by science teams at NASA Goddard and processed into Level 2 precipitation retrievals using algorithms developed with collaborators at University of Washington, University of Tokyo, and Georgia Institute of Technology. Higher‑level merged products assimilate radiometric retrievals into precipitation analyses produced by modeling centers such as European Centre for Medium-Range Weather Forecasts, United Kingdom Met Office, and Japanese Meteorological Agency. Data distribution leverages archives at NASA Earthdata and mirror sites used by PANGAEA and research groups at University of Colorado. Standard products include instantaneous precipitation rate, snowfall masks, and hydrometeor profiles, formatted for use with assimilation systems and decision support tools employed by agencies like US Geological Survey and World Food Programme.
The instrument supports studies across atmospheric science, cryospheric research, and hydrology, underpinning investigations by researchers at Harvard University, Princeton University, and Imperial College London. Applications include improving quantitative precipitation estimation over oceans and high latitudes where ground radar is sparse, characterizing convective systems studied by field programs such as TOGA and DYNAMO, and constraining microphysical model parameters used in models from NOAA GFS and ECMWF IFS. The radiometer has been used to analyze tropical cyclone precipitation structure for studies by National Hurricane Center and to monitor snow and solid precipitation relevant to agencies like International Association of Hydrological Sciences.
Deployed aboard the GPM Core Observatory, the instrument began operations after launch during a commissioning phase coordinated with teams from JAXA, NASA Goddard, and contractors including Lockheed Martin. It functions within the broader GPM mission that involves a constellation of partner satellites from agencies such as Indian Space Research Organisation, China National Space Administration, and Korea Aerospace Research Institute. Operationally, the instrument has been integrated into near‑real‑time processing streams supporting flood forecasting initiatives at United Nations offices and national services including India Meteorological Department.
Limitations stem from footprint size, sensitivity to surface emissivity over complex terrain and coastal zones, and difficulties retrieving light precipitation and mixed‑phase hydrometeors, issues also encountered by instruments like SMAP and AMSR2. Calibration drift, radio frequency interference from commercial transmitters, and orbit maintenance constraints involving partners such as United Launch Alliance and Arianespace have required mitigation strategies. Validation over remote regions depends on limited ground networks such as those operated by Polar Science Center and international field campaigns coordinated with WCRP.
Category:Earth observation satellite sensors