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題名 | 應用微波資料估計臺灣附近地區降雨之研究=Using Microwave to Estimate Rainfall Near Taiwan Areas |
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作者 | 王光華; 劉振榮; | 書刊名 | 航測及遙測學刊 |
卷期 | 3:3 1998.09[民87.09] |
頁次 | 頁39-66 |
分類號 | 328.886 |
關鍵詞 | 微波; 降雨量; Microwave; Rainfall; SSM/I; |
語文 | 中文(Chinese) |
中文摘要 | 應用微波於大氣遙測是近年來衛星遙測的一大技術突破,因為微波可以提供了更 多的大氣降雨資訊,並且廣範的應用於全球降雨量的研究。本研究目的在提出降雨估計方法 並改善降雨估計準確率、以利防災工作。由於影響微波傳遞的因子很多,如地面發射率、大 氣溫度、雲高、水汽含量、液態水含量、冰晶含量、雨量及這些因子的垂直分佈等。 SSM/I 的資料僅有 7 個頻道,求解這麼多非線性相關的未知數是很複雜的問題。 本研究配合 GMS 衛星及探空資料求得雲高、大氣溫度、結冰高度、冰晶含量, 再由 SSM/I 資料以統計方法 求得海上風速、液態水總含量、水汽含量等來設定大氣初始條件。反演方法則假設大氣的水 在垂直方向是以指數形態分佈,修改原來的線性聯立物理反演法為非線性反演法,並以 SVD 求極小值的解。因為衛星與地面雨量觀測在特性上有很大的不同,為了資料的驗證,假設雨 量是 lognormal 分佈而採用面積時間積分法求陸地的面積雨量, 海上使用雷達資料和衛星 的反演結果做比較。使用臺灣地區一整年的降雨案例。研究結果顯示本研究的模式方法在大 部份的雨量反演結果的精確度確實比過法一般的統計法好。在颱風賀伯的案例中顯示當風速 高於每秒 30 公尺及雨量在 50 mm/hr 以上時對於微波估計降雨會造成較大的偏差,表示可 能已接近微波輻射儀的飽和狀態。大雨則受到地形的影響。 |
英文摘要 | Microwaves form satellites can be used for rainfall rate retrieval by two different methods-- a statistical based algorithm or a physical based algorithm. Until now the statistical based algorithm has been more frequently applied because it is less complicated. However, the physical based algorithm provides the best method to reduce estimation retrieval bias. It can be simplified by reducing the number of unknown parameters such as surface emissivity, water vapor content, temperature profile, and cloud height, GMS infered data and RAOB data were used to estimated some atmospheric parameter and which were treated as known parameters. The most uncertain factor is surface emissivity over land which was resolved by NDVI( Normalized Differential Vegetation Index) . Of the many physical based methods, the nonlinear simultaneous algorithm of determining rainfall rates proved to be the best. Rain gauge data over land was compared with satellite retrieved data. Area rainfall rate determined by the ATI (Area Time Integral) method was considered as ground true. The accuracy of the rainfall retrieval results in whole 1996 near Taiwan area were compared, most of nonlinear retrieval method are better than SI method which is the best statistical method in Taiwan area. The accuracy of stratus rain rate estimation was worse than cumulus rain rate estimation because cloud structure was difficult to determine and the cumulus pattern was assumed is all cases. Also when instant wind speed exceeded 30m/s and rainfall rate was over 50 mm/hr, SSM/I rain information was reduced for it is close to instrument saturation. |
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