本研究利用MODIS Aqua / Terra 在2002年至2008年發生在亞洲地區的生質燃燒、沙塵暴事件以及冰島火山爆發事件之觀測資料，分析各類氣膠在可見光及紅外頻道之輻射特性，並歸納出各類氣膠之光學特性，以建立辨識氣膠種類之方法。 由MODIS 36個頻道輻射特性之分析結果得到可利用第2(850nm)、3(469nm)、8(413nm)、9(443nm)與17(905nm)頻道區分煙塵與晴空地表之不同，利用第25(4.52μm)及26(1.38μm)頻道區分沙塵和火山灰與晴空地和煙塵，以及利用第17與第18(936nm)頻道區分沙塵與火山灰。在紅外頻道方面，沙塵和火山灰之11μm與12μm亮度溫度差(BTDI)明顯低於煙塵，沙塵(-1.729±1.001)及火山灰(-2.395±0.646)皆為負值，而煙塵(3.408±0.141)則為正值，因此可就BTDI值區分煙塵與另外兩者。此外本研究亦發現衛星觀測之BTDI值與氣膠(沙塵和火山灰)濃度及環境水氣含量有關，因此可利用衛星所觀測到之BTDI值以及環境水氣含量，估算沙塵與火山灰在像元裡之比例。本研究依照各類氣膠在MODIS三十六頻道之特性、BTDI值及氣膠在像元裡之比例，建立一套辨識煙塵、沙塵以及火山灰之方法，並應用於亞洲地區不同的氣膠種類之辨識，獲得不錯之結果。 The main aim of study is to identify aerosol types based on the spectral radiance observed by Moderate Resolution Imaging Spectroradiometer (MODIS). Three datasets are collected for the discrimination of aerosol types, including volcanic ash, smoke plumes and mineral dust, during the periods of Icelandic volcano eruption, Southeast Asian biomass burning and Asian dust storm events. According to the analysis of thermal radiation (brightness temperature), the BTDI (Brightness Temperature Difference Index) in split window of smoke plumes (3.408±0.141) are larger than both volcanic ashes (-2.395±0.646) and dust particles (-1.729±1.001), suggesting that the BTDI can be an optimal indicator for the discrimination of smoke from volcanic ash and dust particles. For the radiometric characteristics in visible and near infrared spectral band, smoke plumes and clean land surface have a distinct difference in reflectivity in MODIS band 2 (850nm), band 3 (469nm), dand 8 (413nm), band 9 (443nm) and band 17 (905nm). Therefor, these bands can be an optimal indicator for the discrimination between smoke plumes and land surface. Dust particles and volcanic ashes have a distinct difference in reflectivity between band 17 ( 905nm ) and band18 ( 936nm ) of MODIS and the difference between these two bands can be an optimal indicator for the discrimination between volcanic ash and dust particles. On the other hand, the BTDI observed by satellite is composed of contribution by aerosol (dust and ash) and water vapor in the environment if a pixel cell is not full filled with aerosol particles. Therefor, we can derive the fractions of BTDI contributed by aerosols and water vapor. As a result, an ensemble method for diseriminating the aerosol type has been integtated in this study.
