[A-AS08] General Meteorology

[AAS08-09] Verification of Precipitation Intensity Estimation Accuracy in Ku-Band Dual-Polarization Radar

*Taigo Hayakawa¹, Yuuki Wada¹, Daichi Kitahara¹, Yoshitaka Nakamura², Toshio Iguchi¹, Tomoo Ushio¹ (1.Osaka University, 2.Kobe City College of Technology)

Keywords:Weather radar, Precipitation, Ku-Band, Dual-Polarization

In Japan, there are currently around 60 operational weather radars, many of which have been upgraded in recent years with dual-polarization capabilities to enhance precipitation estimation accuracy. However, despite these advancements, predicting localized and sudden weather events such as tornadoes and heavy downpours remains challenging, and the associated damages can be significant. To mitigate such damages, it is crucial to predict and detect these localized extreme weather events early and understand their underlying principles. Therefore, it is desirable to further refine the existing weather radar network by deploying medium-range radars with high temporal and range resolutions. With the above background, our research group developed a Ku-band dual-polarization weather radar. The radar under consideration is a medium-range and high-resolution system with an observation range radius of 20 km, temporal resolution of 1 minute and minimum range resolution of 2.4 m. It operates at the Ku-band frequency (15.75 GHz), which is higher than that of conventional weather radars in Japan (C-band: 5 GHz, X-band: 9.7 GHz). Currently, there are limited instances of Ku-band dual-polarimetric radar observations in Japan, and no established method exists for estimating precipitation intensity or assessing its accuracy. This study employs three methods (Z-R method [1], Z-KDP method [2], and Z-PHI method [3]) to estimate precipitation intensity from Ku-band dual-polarimetric radar observations. The accuracy of these estimated values was evaluated by comparing them with data from an optical disdrometer, a type of ground-based rain gauge.

The results of the accuracy evaluation indicate that the Z-R method can accurately estimate precipitation intensity within the range of 0–2 mm/h. In case of strong rainfall, this method tends to underestimate rainfall intensity due to rain attenuation effects. The Z-KDP method demonstrates capability in estimating precipitation intensity in high rainfall areas with high signal-to-noise ratio (SNR) and it can also capture localized and short-term heavy rainfall events. When this method is applied to weak rainfall, estimation becomes difficult due to the reduced SNR, especially for rainfalls of 3 mm/h or less. The Z-PHI method shows stable estimation of precipitation intensity within the range of 0–10 mm/h, regardless of the rainfall pattern. In case of localized and short-term heavy rainfall, this method tends to underestimate. Therefore, it is considered desirable to use in conjunction with the Z-KDP method. Based on these findings, future research will focus on refining algorithms for calculating precipitation intensity using Ku-band dual-polarimetric weather radar to achieve highly accurate observations.

[1] J.S.Marshall, R.C.Langille, and W.M.K.Palmer, “Measurement of rainfall by radar”, Journal of Meteorology, vol.4, no.6, pp.186-192, 1947.
[2] Haonan C. and V. Chandrasekar, “Estimation of light rainfall using Ku-band dual-polarization radar”, IEEE Trans. on Geoscience and Remote Sensing, vol.53(9), pp. 5197-5208, 2015.
[3] J.Testud, E.L.Bouar, E.Obligis, and M.Ali-Mehenni, “The rain profiling algorithm applied to polarimetric weather radar”, Journal of Atmospheric and Oceanic Technology, vol.17, no.3, pp.332-356, 2000.