利用衛星資料推估中國大陸與台灣地區地表反照率研究

Abstract

摘要 利用地球同步氣象衛星可見光頻道窄譜的反照率推估，可藉地表與大氣環境中雲系的反照率灰度值不同區間分布特性，決定灰度門檻值，保留大部份地表的反照率灰度值。為得到晴空地表之反照率，必須去除雲系的干擾影響，同時引進紅外線頻道表面亮度溫度與地面實際觀測氣溫的溫度偏差濾雲法，由兩者之間的溫度偏差量，將可見光頻道地表反照率雲區影響部分濾除，獲得晴空之平均窄譜表面反照率。 經NCEP氣候資料庫的5年平均氣候反照率數據資料的再分析，與同步衛星平均窄頻反照率之統計分析，顯示兩者具有高度正相關結果，相關係數r=0.94，迴歸方程為αNCEP = 1.675 ＋ 0.875αGMS 。由此迴歸修正方程可訂正衛星窄譜反照率資料，得到寬譜之平均地表反照率。 地表反照率的分布與降雨、氣象條件、地表狀況有顯著的相關性。中國大陸青藏高原、內蒙河套與中國東北地區持續存在降雨偏少且相對地表乾燥的高反照率區域，因此內蒙河套一帶為春季發生沙塵暴的源地。華中以南由於降雨集中的結果使得，因此地表反照率明顯偏低。台灣地區東部、東南部、西部與西南部反照率為全年較高地區，山區與部份西南、東北部地區有相對較低反照率表現；另外在台灣附近海域之島嶼亦出現較高反照率情形。 由衛星推估結果顯示，水體反照率為3~10%；其次為潮濕地表，平均反照率為8~15%；乾燥表面則有相對較高12~27%反照值。大氣環境中的對流雲反照率最高，約為33~79%；其次為霧區與層雲，反照率為23~58%；高層雲因其透光特性，故反照率較低，約為15~42%。

Abstract The estimation of the narrow-band albedo from the visible channel of the GMS Satellite can be made by deciding the gray scale, which can be derived from the different distribution characteristics of the albedo ranges for the surface and the cloud systems in the atmosphere. In order to get the albedo of the fair-sky surface, the disturbances caused by the cloud systems should be eliminated, and at the same time, the temperature of the infrared channel surface brightness and the method of the cloud filtering on the temperatures of the actual surface observations should be included. From the amounts of the temperature deviations between the two, the albedo of the cloud-affected areas of the visible channel can be eliminated, and the fair-sky average surface albedo of the narrow-band can be gained. Through reanalysis of the 5-year average climatological albedo data from the NCEP Climatological Database and the statistical analysis of the average narrow-band from the GMS Satellite, it appears that there exists a highly correlated relationship between the two, and the correlation coefficient r=0.94, the regression equation is αNCEP = 1.675 ＋ 0.875αGMS. By applying this corrected regression equation, the data from the satellite narrow-band albedo can be corrected and the average surface albedo of the broad-band can be gained. There is a significant interrelationship among the distribution of the surface albedo, precipitation, meteorological conditions and the surface conditions. The Tibetan Plateau of the Mainland China Her-teau, interior Mongolia and the northeastern area of the Mainland China keep a phenomenon of deficient precipitation with also high albedo areas of dry surfaces; therefore, areas around Herteau and interior Mongolia appear to be the source places for the spring sandstorms. Areas to the south of the central Mainland China, it is due to the result of the concentration of the precipitation which makes the humidity of the soil to elevate, and the colors of the soils are getting darker; therefore, the surface albedo significantly deviates toward a low value. From the estimation results of the satellite, it appears that the albedo of the water is 3~10%, damp area is 8~ 15% and arid area is 12~27%. The highest albedo values, which rank 33~79%, in the atmosphere belong to the convective clouds; the second place whose albedo is 23~58% goes to the fog areas and the stratus; due to the transparency of the cirrus clouds, it has a lower albedo, about 15-42%.