Calibration of the GPM/DPR

The Global Precipitation Measurement (GPM) mission consists of the GPM Core Observatory and the constellation satellites. The GPM Core Observatory carries the Dual-frequency Precipitation Radar (DPR) and the GPM microwave imager (GMI). The DPR has Ku-band precipitation radar (KuPR) and Ka-band precipitation radar (KaPR) which were developed by Japan Aerospace Exploration Agency (JAXA) and National Institute of Information and Communications Technology (NICT). The satellite bus and the GMI were developed by National Aeronautics and Space Administration (NASA). The GPM core observatory launched at 3:37 on February 28, 2014 (JST) from Tanegashima Space Center in Japan. This paper reviews the calibration of the latest product version (V5) of the DPR.

The DPR has been calibrated several times on orbit with the Active Radar Calibrator (ARC) since the GPM core observatory was launched. Based on these calibrations, the value of some calibration parameters of the DPR was re-examined in V5. Major changes of the DPR’s calibration in level 1 products are listed as follow.

• New receiver and transmitter gains.
• New beam widths and pulse widths.
• Correction for the range distance. 

As a result, the values of the measured radar reflectivity factor (Zm) increases by about 1.3 dB and 1.2 dB for KuPR and KaPR relative to it estimated with calibration parameters of at launch, respectively. The paper will explain these changes and the results of the calibration.