| Summary: | 碩士 === 國立中央大學 === 太空科學研究所 === 99 === 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.
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