Dual-frequency Precipitation Radar (DPR)
One of the prime instruments for the GPM Core Observatory is called the Dual-frequency Precipitation Radar (DPR). The DPR consists of a Ku-band precipitation radar (KuPR) and a Ka-band precipitation radar (KaPR). The KuPR (13.6 GHz) is an updated version of the highly successful unit flown on the TRMM mission (shown below). The KuPR and the KaPR will be co-aligned on the GPM spacecraft bus such that that the 5 km (3.1 mile) footprint location on the earth will be the same.
Data collected from the KuPR and KaPR units will provide 3-dimensional observations of rain and will also provide an accurate estimation of rainfall rate to the scientific community. The DPR instrument will be allocated 190 Kbps bandwidth over the 1553B spacecraft data bus.
DPR Instrument Details
The DPR is a spaceborne precipitation radar capable of making accurate rainfall measurements. The DPR is expected to be more sensitive than its TRMM predecessor especially in the measurement of light rainfall and snowfall in high latitude regions. Rain/snow determination 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 is also expected to increase the number of samples at each IFOV to realize a 0.2 mm/h sensitivity.
The KuPR and KaPR, together with GMI, are the primary instruments on the GPM spacecraft. These Earth-pointing KuPR and KaPR instruments will provide rain sensing over both land and ocean, both day and night.
Top-level general design specifications are as follows:
|Swath Width||245 kilometers (km)||120 kilometers (km)|
|Range Resolution||250 meters (m)||250/500 meters (m)|
|Spatial Resolution||5 km (Nadir)||5 km (Nadir)|
|Beam Width||0.71 degrees||0.71 degrees|
|Transmitter||128 Solid State Amplifiers||128 Solid State Amplifiers|
|Peak Transmit Power||1013 Watts (W)||146 Watts (W)|
|Pulse Repetition Freq. (In nominal operations mode)||4100 to 4400 Hertz||4100 to 4400 Hertz|
|Pulse Width||two 1.667 microseconds (µs) pulses||two 1.667 microseconds (µs) pulses in matched beams two 3.234 microseconds (µs) pulses in interlaced scans|
|Beam Number||49||49 (25 in matched beams and 24 in interlaced scans)|
The DPR instrument is 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) is designing and testing the radars under the direction of JAXA and NICT.