Our international partner, Japan Aerospace Exploration Agency (JAXA), is developing one of the prime instruments for the GPM Core Observatory—the Dual-frequency Precipitation Radar (DPR). The DPR consists of a Ku-band precipitation radar (KuPR) and a Ka-band precipitation radar (KaPR). The DPR instrument is being developed by JAXA in collaboration with the National Institute of Information and Communications Technology (NICT). NEC Toshiba Space Systems, Ltd. (NTSpace) is the contractor responsible for designing, manufacturing, and testing the DPR.

The DPR is a spaceborne precipitation radar capable of making accurate rainfall measurements. The DPR is expected to be more sensitive than its predecessor, the TRMM Precipitation Radar (PR), so that it can detect light rainfall and snowfall which are dominant especially in the high latitude regions. Rain/snow discrimination is expected to be accomplished by using the differential attenuation between the Ku-band and the Ka-band frequencies. The variable pulse repetition frequency (VPRF) technique has been adopted to increase the number of samples at each Instantaneous Field of View (IFOV) to realize a 0.2 mm/h sensitivity.

The KuPR and the KaPR will be co-aligned on the GPM spacecraft bus such that their 5-km footprint locations on the earth will be the same. The swath widths and scan geometry of the DPR and the GMI are shown in Figure 1.

Figure 1: Swath widths and scan geometry of the GPM DPR and GMI instruments (Courtesy of JAXA/NICT)

The layout of the KuPR and KaPR instruments are shown in Figures 2 and 3 respectively.

A 190-Kbps bandwidth will be allocated to the DPR instrument over the 1553B spacecraft data bus. The DPR data will be transmitted to the ground using NASA's Tracking Data Relay Satellite System (TDRSS) multiple access (MA) and single access (SA) services. Ground processing of DPR data will provide a detailed, 3-dimensional, accurate distribution of precipitation over both land and ocean during day and night to the scientific and operational user communities. DPR data will also play a key role in improving the accuracy of precipitation measurements made with Microwave Water Radiometers (MWRs) on GPM constellation satellites. As a result, the user communities will benefit from receiving accurate 3-hourly global precipitation maps for applications in areas such as, but not limited to, improved weather forecasts, flood forecasting, climate change assessments, and water resource management.

The development of the DPR is progressing well. KaPR breadboard model (BBM) testing has been successfully completed. Work has begun on the KaPR electrical model (EM) in preparation for the RF-link tests scheduled for January 2006. BBM testing for the KuPR is also complete, with the EM buildup activity to commence soon. Figure 4 shows pictures of the KuPR and KaPR BBMs. Figure 5 shows photos of some components of the KaPR EM.

Figure 4: Breadboard Models (BBMs) for the KuPR and KaPR (Courtesy of JAXA/NICT)

Figure 5: KaPR Electrical Model (Courtesy of JAXA/NICT)

By JAXA

For additional information, please contact Clyde Woodall (clyde.h.woodall@nasa.gov).

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