雙偏極化雷達的觀測資料會受雨滴大小、形狀、傾斜角度塑形所影響，並能藉此特性來提供雨滴粒徑分布(Drop Size Distribution, DSD)以及降雨資料。在Gamma DSD假設下(N(D)=□□□)，DSD的控制參數μ和□之間會有一約束關係存在，Zhang et al.(2001)利用此約束關係搭配S-Band雙偏極化雷達所觀測到之回波(reflectivity, □)、差異反射率(differential reflectivity, □)來反演DSD進而計算降雨率，藉此來提升降水估計之準確性。本研究利用中央大學C-Band雙偏極化雷達資料對冬颱南瑪都(NANMADOL)做降水估計，除了使用Zhang et al.(2001)之方法外，並另行嘗試加入比差異相位差(Specific differential phase shift;□)此資訊來做反演，結果顯示反演過程中使用□在強降水時的表現優於使用□。相較於利用經驗公式求降雨率，使用此法的優點除了能改善降水估計外，還能獲得Gamma DSD的三個控制參數供雲物理探討及預報模式使用。

High time resolution C-Band polarimetric Doppler radar data from the measurement of NANMADOL typhoon rain were analyzed to study the algorithms for retrieving rain rate. A constrained relation between the shape (μ) and slope (□) parameters will appear when the drop size distribution (DSD) is assumed to be a Gamma distribution. In this study, the constrained relation and two of the three radar parameters: reflectivity (□)、differential reflectivity (□) and specific differential phase shift (□) were used to retrieve the DSD and rain rate. The result showed that, using of □ is much better than □ in heavy rain, and the retrieved accumulative rain agree with the measurements of raingauges very well. The method shows improvement over the existing method using to estimate rain rate in heavy rain and it can provide Gamma distribution for research of cloud physics.