GPM-Core

GPM-Core [NASA]

The Global Precipitation Measurement (GPM) is a follow-on mission to the Tropical Rainfall Measuring Mission (TRMM). GPM is one of the earth observation satellite programs, mainly initiated by the Japan Aerospace Exploration Agency (JAXA), the National Institute of Infomation and Communications Technology (NICT) and the National Aeronautics and Space Administration (NASA).

GPM is, like TRMM, composed of one sun non-synchronous orbit satellite-borne precipitation radar and a microwave scanning radiometer, and more than one sun synchronous orbit microwave scanning radiometers in a constellation of other satellites.

The core satellite is expected to be able to measure detailed precipitation activities, using both ofthe dualfrequency precipitation radar and the microwave scanning radiometer. The data acquired by such measurement will permit of sophisticating the presumed algorithm of quantitative rain measurement in the microwave scanning radiometer. The sub-satellite will conduct the precipitation measurement of the microwave scanning radiometer and the measurement will become more reliable by utilizing the presumed algorithm.

The sub-satellite constellation was launched by NASA, European Space Agency (ESA) and other space organizations in the world. The number of satellites will be around eight. It is possible to get a global rainfall distribution in every 3 hours when the microwave scanning radiometers aboard these 8 polar orbit satellites collect and process the data. GPM plans real-time transmission of the global rainfall distribution data. This real-time data can be utilized not only for scientific research, but also for weather forecast, flood prediction, water resource management.

The major sensors on the GPM primary satellite are the dual-frequency precipitation radar (DPR) and the microwave radiometer (GMI). The DPR consists of two radars, a TRMM/PR-type precipitation radar with a frequency of 13.6 GHz, and a 35.5 GHz precipitation radar that is added to improve the sensitivity and accuracy of measurement. The GMI will be an improved model of the TRMM Microwave Imager (TMI). The roles of the GPM primary satellite are to collect as much microphysical information as possible for accurate rain estimation by performing synchronous observation with the GMI and the DPR, and to provide calibration standards for the other microwave radiometers on the constellation satellites.

The 13.6 GHz channel of the DPR has a swath width of about 245 km, and the 35.5 GHz channel observes a swath width of about 100 km. In the overlapping area, measurements will be performed synchronously. The GMI scans its antenna conically with a swath width of about 800 km.

The Core Spacecraft was developed in-house at NASA GSFC with the avionics procured through Goddard's Rapid Spacecraft Development Office (RSDO). In March 2005, NASA chose Ball Aerospace & Technology Corporation to provide the GMI instrument. The DPR instrument was being developed by Japan Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT) for a flight on the GPM Core Observatory. NEC Toshiba Space Systems, Ltd. (NTSpace) designed and tested the radars under the direction of JAXA and NICT. JAXA provides the H-2A launch vehicle.

The Global Precipitation Measurement constellation is a joint venture between NASA and the Japan Aerospace Exploration Agency (JAXA), the Indian Space Research Organisation (ISRO), the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), France’s Centre National d’Études Spatiales (CNES) and the United States National Oceanic and Atmospheric Administration (NOAA).

The GPM constellation consists of consists of nine other spacecraft in orbit with four more awaiting launch:

• TRMM (NASA, JAXA)
• DMSP-5D3 F17, 18, 19, 20 (USAF)
• NOAA 18, 19 (NOAA)
• Suomi NPP, JPSS 1 (NOAA)
• METOP B, C (EUMETSAT)
• Megha-Tropiques (CNES, ISRO)
• GCOM-W (Shizuku) (JAXA)

The GPM-Core satellite will serve to provide a reference point with which the rest of the constellation’s data can be calibrated.