Tsukuba Incentive Award (20**)
Research Theme: Development of rainfall estimation by using multi-parameter radar
Research Background and Achievements:
Rainfall information for a flood monitoring is estimated by Z-R relationship (where Z is reflectivity, and R is rainfall intensity) with conventional weather radar data. The relationship has been standardly used for half a century; however the relationship depends on rainfall types and causes the under-estimation by radio wave attenuation. So the rainfall intensity estimated by the conventional radar is calibrated by ground-based rain gauge data. But because the rain gauge calibration takes tens of minutes, it is difficult for the conventional radar to monitor a localized heavy rainfall which develops rapidly. Moreover the estimation accuracy tends to be bad in mountain or sea areas, where there is a few or no rain gauge.
This research solved these problems by using X-band Multi-Parameter (MP) radar. The MP radar utilizes two types of radio waves: horizontal and vertical polarizations, though the conventional radar uses a horizontal polarization only. When these two types of polarizations propagate in a rainfall area, a phase difference between these polarizations (differential phase shift) appears. By a scattering simulation and analysis of MP radar observation data, they indicated that the rainfall type dependency of the rainfall estimation by using a differential phase shift per unit distance (specific differential phase shift; KDP) is more insignificant than that of the Z-R relationship and that the KDP method has enough accuracy without the rain gauge calibration.
According to this achievement, Ministry of Land, Infrastructure, Transport and Tourism started to deploy MP radars in three great urban areas (Tokyo, Nagoya and Osaka) and local major cities. The radar network system has been operated experimentally since FY2010. This system uses data processing software and rainfall estimation algorism developed in this research. This first deploying of operational MP radar network is greatly concerned by disaster prevention organizations, local governments and companies inside and outside Japan.
As a result of these pioneering works, they have been selected as a winner of the 21th Tsukuba Incentive Award.