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Continuity of 3B42 and 3B42RT (G. J. Huffman and L. S. Chiu, 11/5/2004)
The TRMM Multi-satellite Precipitation Analysis (MPA; 3B42RT and 3B42) produces three hourly rain rates at 0.250 latitude by 0.250 longitude grid covering 500S to 500N. The input data for this merged product include a merged intercalibrated
microwave-only product (3B40RT) and an Infrared rain product that is calibrated using microwave rain rates (3B41RT). Currently, 3B40RT is generated using rain rate estimates from microwave measurements from the TRMM sensors and the Special
Sensor Microwave Imagers on board the DMSP satellites using the Goddard Profiling Algorithm (GPROF). 3B41RT is based on infrared measurements from geostationary satellites that are calibrated using microwave rain estimates. The 3B42RT estimate
consists of the merged microwave estimate within the 3 hourly 0.25 degree space/time grid when available, and the calibrated IR rain rates otherwise.
In the next version of 3B42RT (and the new version of 3B42), microwave data from the Advanced Microwave Scanning Radiometer (AMSR) on board NASA's Aqua satellite and the Advanced Microwave Sounding Unit (AMSU) on board the NOAA-series satellites
will be included in 3B40RT.
Currently, the TRMM coverage is about 25% of all microwave estimates. The addition of AMSR and AMSU will reduce the TRMM contribution to about 15%. Hence we expect some degradation in 3B42 and 3B42RT performance after the shutdown of
TRMM due to the direct loss of the TRMM microwave estimates from 3B40RT. However, we expect the intercalibration of all the remaining microwave estimates and consequently the microwave calibration of the IR estimates to be stable.
The quantitative impact of shutting down TRMM has not been assessed for the MPA, but is expected to be manifested mostly as additional uncertainty in the finest time and space scales.
Global Precipitation Measurements (GPM)
GPM is a cooperative mission between NASA, the National Space Development Agency (NASDA) of Japan now known as Japan Aerospace Exploration Agency (JAXA), and other international partners. Building on the success of the Tropical Rainfall Measuring Mission (TRMM), GPM, via a constellation of small satellites, will continue measurement of global precipitation, a key climate factor. Its science objectives are to improve ongoing efforts to predict climate by providing near-global measurement of precipitation, its distribution, and physical processes; to improve the accuracy of weather and precipitation forecasts through more accurate measurement of rain rates and latent heating; and to provide more frequent and complete sampling of the Earth's precipitation.
GPM will answer the following questions under NASA's Earth Science Enterprise major category of "How Does Precipitation Impact Our Changing Earth?"
- How are global precipitation, evaporation, and cycling of water changing?
- What are the effects of clouds and surface hydrologic processes on Earth's climate?
- How are variations in local weather, precipitation, and water resources related global climate variation?
- How can weather forecast duration and reliability be improved by new space-based observations, data assimilation, and modeling?
- How well can transient climate variations be understood and predicted?
- How well can long-term climactic trends be assessed or predicated?
Applications:
- Agricultural efficiency
- Disaster management
- Water management
Launch:
Design Life:
Orbit:
- Approx. 600 km (Primary and Costellation sattelites)
- Sun-Synchronous (Primary and Constellation sattelites)
- Inclination: Approx. 68 degrees (Primary sat.) ; Approx. 90 degrees (Costellation sat.)
- Period: 92 minutes (Primary sattelite); 100 minutes (Constellation sattelites)
Instruments:
Horizontal Resolution
- KuPR Instrument: 245 km (Primary sattelite); Approx. 800km (Constellation sattelites)
- KaPR Instrument: 120 km (Primary sattelite)
Range Resolution
- 250 m (Primary sattelite)
Measurements:
- Global precipitation
- Cloud structure and precipitation characteristics including rain rate, cloud type, 3D cloud structure, and drop-size distribution
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Atmos Composition
