Environmental Sciences Department Seminar

The core satellite of Global Precipitation Measurement (GPM), which is scheduled to launch in 2014, has a dual-wavelength precipitation radar (DPR). DPR consists of Ku and Ka radars. Ka-band radiowave suffers from strong attenuation for rain and strong Mie scattering effect for snow. Because ground measurements of precipitation (rain and snow) at Ka-band are limited, measurements of backscattering and extinction characteristics of precipitation are necessary for the GPM/DPR algorithm development. For the ground validation of the GPM/DPR, a dual Ka-band radar system was developed by the Japan Aerospace Exploration Agency (JAXA). The Ka radar system consists of two identical Ka radars. When the Ka radars face each other and observe the same precipitation system between the radars with opposite direction, both the equivalent radar reflectivity factor (Ze) and specific attenuation (k) can be measured at each range bin of the path. The measured k-Ze relations of rain, snow, and the melting layers can be used to develop the "scattering table" for the improvement of the GPM/DPR algorithm performance. Observations for both rain and snow using the dual Ka-radar system are ongoing in several locations in Japan. Results of measurements of k-Ze relations of rain and snow are presented. Performance of the system are evaluated by comparing measured Ze and k of rain with those estimated from the disdrometer. Although some biases in Ze exist, the measured k-Ze relations are reasonable. Among snow events, different tendencies of k-Ze plots appear depending on surface temperature. The difference of k-Ze relations of snow is attributed to the difference of the backscattering and attenuation characteristics between wet and dry snow. Moreover, as a transformation of the dual Ka observation, a vertical-slant direction observation for melting layer is proposed. The configuration is that one radar was directed in vertical and the other was in