744 Development of Multiple-Parameter Phased-Array Weather Radar

Tuesday, 8 January 2019
Hall 4 (Phoenix Convention Center - West and North Buildings)
Tetsuya Kobayashi, Toshiba Infrastructure Systems and Solutions Corporation, Kawasaki, Japan; and F. Mizutani, M. Wada, A. Yamada, H. Goto, A. Watanabe, N. Takahashi, H. Hanado, and T. Ushio

For the conventional weather radar with parabolic antenna, transmitter and the method of radar observation were mainly developed. Transmitters used in weather radar have been changing from electron tube to solid-state type. Because with Solid-state transmitters, it is not necessary to change the electron tubes as it is required for magnetron or klystron-based radars. About the method of radar observation, the type of weather radar has been changing to dual-polarization Doppler weather radar that can obtain more observation parameters by using horizontal and vertical polarized waves.
On the other hand, weather radars networks were deployed in several region and country. These radar networks, such as the Next Generation Radar (NEXRAD) network composed of 122 S-band weather radars, contribute to analyze the meteorological phenomena and reduce the damage of the weather disaster. In Japan, Ministry of Land, Infrastructure, Transport and Tourism (MLIT) operates collaborated radar network with X-band and C-band dual-polarization Doppler weather radars to monitor rainfall amount near major rivers and urban areas. Japan Meteorological Agency (JMA) also operates the C-band Doppler weather radar network all over Japan.
However, in spite of the high accuracy observation by using parabolic radar networks and dual polarization, it is difficult to reveal occurrence and development process of meteorological phenomena in detail, such as rapidly developed cumulus clouds, supercell storms and organized precipitation systems. To solve this problem and observe the initial feature of these phenomena, the weather radar needs the function of high accuracy observation and rapid scan in whole three-dimensional observation field.
In 2012, we developed the Single-Polarization Phased Array Weather Radar (SP-PAWR) (Mizutani et al, 2018). This SP-PAWR is able to estimate the rainfall amount and wind speed in whole three-dimensional observation field by using radar reflectivity and Doppler velocity in less than 30 seconds in a range of 60 km. To accomplish the rapid scanning, this SP-PAWR adopts electric scan in elevational and mechanical scan in azimuth rotation. For a transmitted wave of this SP-PAWR, a fan-shaped transmission beam is used. Result of the digital beam forming (DBF) process for receiving in elevation angle, the SP-PAWR can obtain the data of 100 elevation angles. Yoshimi et al. (2018) showed that three dimensional rainfall data observed by SP-PAWR was useful for disaster-prevention work of local government in Japan. However, there were 2 major remaining problems of SP-PAWR, which are a rainfall attenuation correction process and accuracy of rainfall amount estimation.
For a next radar development project in Japan, we completed to develop the dual-polarization phased array Doppler weather radar which named “Multiple Parameter Phased Array Weather Radar; MP-PAWR”. Proto-type MP-PAWR has been installed and started an initial observation in December 2017, at Saitama University in Japan. The frequency is 9.4 GHz (X-band). A scanning scheme of the MP-PAWR is same as the SP-PAWR, which adopts electric scan and mechanical scan in elevation and azimuth, respectively. By transmitting dual-polarized wave, the MP-PAWR provides the dual polarimetric parameters, such as differential reflectivity (ZDR), correction coefficient (CC), differential phase (Φdp) and specific differential phase (Kdp), in whole three-dimensional observation field. These parameters can be obtained in 30 or 60 seconds in a range of 60 or 80 km in real-time, respectively. Additionally, by using these parameters, the MP-PAWR system provides a hydro-metolorogic particle classification and the high accuracy of rainfall estimation with KDP using attenuation correction method.
There were two major issues to develop the MP-PAWR in the initial stage of development. One of the issues was number of antenna elements. Due to the two-dimensional array of antenna elements, the number of elements increases more than that of the SP-PAWR. As a result, the cost of the MP-PAWR increases. Another issue was the cross polarization discrimination (XPD). The XPD decreases when electronic scanning is performed. To solve first issue, we developed the special RF-CMOS exclusively used for weather radar and reduced the cost per element. By improving the feeding method, the MP-PAWR achieved a XPD of 35 dB on the zero-elevation angle, and more than 30 dB on the other elevation angle. Because of 30 dB XPD, horizontal and vertical polarized waves were transmitted simultaneously in the MP-PAWR. During the initial observation, we obtained some interesting results. For example, in the reflectivity field by the MP-PAWR, the influence of the ground clutter is clearly removed with clutter removal algorithm.
We will continue the calibration and verification of the MP-PAWR. We believe that the high efficiency and usability of the MP-PAWR will be proved according to more studies and analyses with observation campaign in the near future.

The authors are grateful to the financial support from the Cross-ministerial Strategic Innovation Promotion Program (SIP) operated by the cabinet office, the Government of Japan.

F. Mizutani, T. Ushio, E. Yoshikawa, S. Shimamura, H. Kikuchi, M. Wada, S. Satoh and T. Iguchi, "Fast-Scanning Phased-Array Weather Radar With Angular Imaging Technique," in IEEE Transactions on Geoscience and Remote Sensing, vol. 56, no. 5, pp. 2664-2673, May 2018.
K. Yoshimi, F. Mizutani, N. Takahashi and T. Ushio, “Development of a Detection System of Heavy Rainfall using X-Band Phased-Array Weather Radar”, in 10th European Conference on Radar in Meteorology and hydrology, 2018, July 2018.

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