以GPS天頂向總延遲量預估大豪雨之可行性評估

Feasibility Assessment of Heavy Rainfall Forecasting using Global Positioning System-Derived Zenith Total Delays

10.29417/JCSWC.201809_49(4).0003

曾子榜(Tzu-Pang Tseng)；蕭宇伸(Yu-Shen Hsiao)；曾莉鈞(Li-Chun Tseng)

全球定位系統 ； 天頂向總延遲量 ； 大豪雨預報 ； Global positioning system ； zenith total delay ； heavy rainfall forecasting

中華水土保持學報

49卷4期（2018 / 12 / 01）

233 - 242

繁體中文

本研究分析全球定位系統(Global Positioning System, GPS)資料所計算之天頂向總延遲量(Zenith Total Delay, ZTD)與降雨之相關性，並評估此方法應用於預報大豪雨之可行性。本研究選擇2015年8月蘇迪勒颱風及9月杜鵑颱風作為研究案例，利用Bernese 5.2軟體以精密單點定位法(Point Precise Positioning, PPP)將17個GPS地面站資料分別計算出颱風期間內之ZTD結果，並與二次差分相對定位(Double-Differencing；DD)所計算之ZTD結果進行比較。本研究亦蒐集颱風期間內中央氣象局雨量站實際降雨資料來分析ZTD與降雨之關聯性。本研究嘗試使用互相關法及ZTD斜率法，分別進行大豪雨預報的可行性評估。研究顯示，互相關法成果不如預期，無法使用在預測大豪雨上；ZTD斜率法皆能在兩颱風案例中，優先於大雨發生前，斜率上有較明顯之變動，因此其未來運用在預測大豪雨上具有潛力。

This study examined the correlation between rainfall and zenith total delays (ZTDs), which are derived from the global positioning system (GPS). Furthermore, this study analyzed feasibility assessment of heavy rainfall forecasting using GPS-derived ZTDs during typhoons. Typhoon Soudelor (in August, 2015) and Typhoon Dujuan (in September, 2015) were selected as the study cases. We used the point precise positioning (PPP) method with Bernese 5.2 software to compute ZTDs at 17 GPS stations during the study periods. The ZTD results derived from the PPP method were compared with those derived from the double-differencing method. We also collected rainfall data from the rainfall stations of the Central Weather Bureau in Taiwan and analyzed correlations between the ZTDs and rainfall at these selected GPS rainfall stations. The cross-correlation method and ZTD-derived slope were used to assess the feasibility of heavy rainfall forecasting. Our results indicated that the cross-correlation method is unfeasible for heavy rainfall forecasting during typhoons. The results of the ZTD-derived slope indicated an obvious ZTD peak (extreme value) before heavy rainfall at each station during the two typhoon events. Therefore, using GPS-derived ZTD for heavy rainfall forecasting has great potential for future application.

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