Cross Sensor Validation of the GPM/DPR with Phased Array Radar at X band

Reflectivity factor observed by the Dual Frequency Radar(DPR) at Ku and Ka band onboard the GPM(Global Precipitation Measurements) core satellite is compared with the reflectiveity by the Phased Array Radar at X band in Osaka University. In the GPM project, the dual frequency precipitation radar (DPR) observes the precipitation system with high temporal resolution. Since the DPR sensor is on the space platform in low earth orbit, the captured 3 dimensional structure of precipitation is a snapshot over the swath of the sensor and hard to be compared with the data from the conventional weather radar system. Because the conventional weather radar system needs at least more than 5 minutes to achieve the 3 dimensional scanning for whole sky. At this point, the fast scanning radar system is required to make a better comparison with DPR and to evaluate the performance of the DPR. A Phased Array Radar (PAR) system that was installed in Osaka University in 2012 has the unique capability of scanning the whole sky with 100m and 10 to 30 second resolution up to 60 km. The system adopts the digital beam forming technique for elevation scanning and mechanically rotates the array antenna in azimuth direction within 10 to 30 seconds. The radar transmits a broad beam of several degrees with 24 antenna elements and receives the back scattered signal with 128 elements digitizing at each elements. Then by digitally forming the beam in the signal processor, the fast scanning is realized. After the installation of the PAR system in Osaka University, the initial observation campaign was conducted in Osaka urban area and the radar system successfully captured the 3 dimensional structure of precipitation system with high temporal resolution, showing the unique capability of the system A compared results show that the data from DPR agree well for reflectivity above the noise level. The reflectivity pattern from DPR matches well with that from the PAR (Fig. 1) and the correlation coefficient is over 0.8 with the bias of less than 1 dB for some case studies(Fig. 2). From these comparisons, the DPR hardware works very well and the measured back scattering coefficients are well measured. On the performance of the DPR algorithm, comparison of the attenuation corrected reflectiveity (Z corrected) shows that the DPR algorithm sometimes underestimates the reflectiveity factor (Fig. 3). Caption Fig1 Vertical cross section of the precipitation system observed by GPM/DRP(left) and PAR(right). Fig. 2 Scattergram of Reflectivity value observed by Ku PR and PAR. Fig. 3. Scattergram of PIA (Path Integrated Attenuation) estimated by PAR and GPM/DPR algorithm. Horizontal axis shows the residuals of corrected reflectiveity minus measured reflectiveity. And Vertical axis shows the PIA at Ku band along the DPR main beam based on the attenuation corrected X band PAR data as a truth.