Availability of three-dimensionally contiguous volume-scan data measured by phased array weather radar

Severe weather disasters caused by localized heavy rainfalls or tornadoes have occurred frequently in Japan in recent years, and have emerged as a social issue. The rapidly-developed localized rainfall is called “guerilla heavy rainfall” by Japanese mass media. We, radar meteorologists or engineers, would like to believe to be able to watch and predict the guerilla rainfall, namely we hope it will not be a surprise attack (i.e. guerilla). Doppler weather radar is a powerful instrument to measure such a severe weather. However, the performance of traditional weather radar is not good enough to detect a small and rapidly changing weather system, because a volume scan by a parabolic antenna requires substantial time of more than 5 minutes. Furthermore, the volume scan of a limited number of elevation angles cannot provide filled data in a three-dimensional space.

NICT (National Institute of Information and Communications Technology) -commissioned research project “Research and development of next-generation Doppler radar” was started. The aim of the project is to develop a rapid-scan radar system using phased-array technique. One of the targets is to measure rain in a three-dimensional space without gap within 10 seconds. Another important target is to develop a low-cost system to become widely used in the near future. As a result of our conceptual design work, we adopt a one-dimensional active phased-array in the elevation direction and a mechanical rotation in the azimuth direction. To increase the number of samples in a limited time, we use a combination of fan-beam transmitting and DBF (Digital Beam Forming) receiving.

To investigate the fine structure and mechanism of rapidly-developed rainfall system, continuous three-dimensional radar data should be necessary. Intermittent horizontal rainfall distribution images (CAPPI) or vertical-slice images (RHI) are not enough to reveal the rapidly evolving rainfall system. Assuming a typical velocity of 10 ms-1, that is a rain particle motion in a horizontal or a vertical direction, we expect that the temporal and special resolutions are, for example, 10 seconds and 100 m respectively. Although the resolutions of 30 seconds and 300 m are also useful, we must chase more fine resolutions. In this study, three-dimensionally contiguous radar echoes will be displayed in some methods to evaluate the utilization. Since the phased-array radar system has not been completed, however, we use the alternative data. We are also promoting this project for not only research use but also practical use through collaboration between industry, academia and government. The application fields of phased-array radar will be extended to short-time forecast or warning to private citizen, river manager, train/airplane operator, and so on. For the different practical users, we should consider the effective utilization method and the useful products of the three-dimensional high-resolution data derived from the phased-array radar.