地球同步衛星MTSAT-1R(Multi-functional Transport Satellite-1R)不但觀測範圍可涵蓋地球表面的四分之一，且可即時提供每半小時的全球觀測資料，非常適合監測大範圍地區的沙塵暴事件。透過分析不同地物在MTSAT-1R衛星各頻道的輻射特性，顯示熱紅外頻道間之亮溫差指數(Brightness temperature difference index; BTDI)於日間可清楚地辨識沙塵覆蓋地區，但在夜間時的辨識能力不佳。因此，本研究加入短波紅外頻道(3.5-4.0μm)希望改進夜間沙塵的辨識能力，以提供全天候亞洲地區沙塵暴的監測能力。而在定量分析方面，為了克服地球同步衛星可見光單一頻道反演氣膠參數的限制，如未知的大氣及地表的反照率。由於海洋表面的反照率極小，在海面反照率為零的假設下，由MTSAT-1R可見光頻道(0.55-0.9μm)資料計算氣膠光學厚度(aerosol optical depth; AOD)的結果與MODIS(Moderate Resolution Imaging Spectrograph)的反演結果具有相當的一致性，顯示此法具有極高的可行性。而在陸地地區，因地表反照率無法忽略，受限於地表雙向反射特性及觀測誤差的影響，研究結果不如預期。因此，未來的研究將著重於地表反照率的求取，期望能達成利用地球同步衛星反演氣膠光學厚度之目標。The observations of geostationary satellite can provide the observation of a quarter of the Earth's surface every half an hour, thus very favorable for monitoring dust storm events. Based on the brightness temperature difference index (BTDI) between the thermal infrared channels, the dust cover areas can be efficiently identified in the daytime. Because of less incoming flux in the nighttime, the BTDI is not clear enough for dust storm detection. Therefore, this study tries to improve the dust storm monitoring with the short wave infrared channel (3.5-4.0μm) during the nighttime, and the results of case studies show the improvement as expected indeed. For the aerosol optical depth (AOD) retrieving over ocean, under the assumption of the sea surface albedo is zero, the AODs retrieved from MTSAT-1R visible channel (0.55-0.9μm) data are quite consistent with MODIS AOD products, indicating highly feasibility of proposed method in this study. However, due to the complex reflectivity and the effect of solar zenith angle, the retrieval of AOD over land surface is not good enough when compared to ground measurements (AERONET data). Therefore, to map the surface albedo accurately for the hourly spatial distribution of AOD with MTSAT-1R data over Eastern Asia will be the next step of this study.
