雷達干涉測量的大氣效應修正: 應用於印度西喜馬拉雅地區;Atmospheric Correction in InSAR Measurement: A Study Case from the Western Himalayas, India

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Title:	雷達干涉測量的大氣效應修正: 應用於印度西喜馬拉雅地區;Atmospheric Correction in InSAR Measurement: A Study Case from the Western Himalayas, India
Authors:	李思儀;LEE,SZU-I
Contributors:	遙測科技碩士學位學程
Keywords:	雷達干涉測量;大氣效應;西喜馬拉雅;InSAR;Himalaya;Atmospheric
Date:	2014-07-24
Issue Date:	2014-10-15 17:16:05 (UTC+8)
Publisher:	國立中央大學
Abstract:	隨著近幾年來遙測技術的發展，雷達差分測量已經成功的應用在觀測地表變形，此技術有幾項特性，例如可不受氣候與日夜影響拍攝，且因為雷達影像的圖幅及衛星的軌道週期，使得此技術可以大範圍及快速的觀測，並基於合成孔徑雷達影像，此技術可以取得高精度的地表形變到達釐米級的結果。但是此技術存在著一些誤差影響，其中一項就是我們主要探討的大氣效應，在雷達波傳遞經過大氣層時會受到水氣影響，而對於C波段雷達影像的差分測量，大氣濕延遲的影響劇烈，因此本研究對於雷達差分測量的大氣效應做修正，並應用於印度西喜馬拉雅區域。本研究使用兩個方法去修正大氣效應: (1) 利用光學影像的水氣資料對雷達差分測量做修正 (2) 利用一時間系列的雷達差分測量得到較穩定的雷達回波資訊，再利用對時間的高通濾波及空間的低通濾波去估計去除雷達差分測量的誤差效應。印度西喜馬拉雅地區位於歐亞板塊及印度板塊逆衝擠壓帶，造成此地區的複雜構造且地表活動較劇烈，研究區域位於印度西喜馬拉雅地區的北阿坎德邦的中南部，此地區的構造包含了因板塊擠壓造成的系列逆衝斷層及轉型斷層等，但因此地區的植被覆蓋、GPS及地震資料缺乏和研究較少，以至於此區域的地表形變量難以測量，因此我們利用修正大氣效應後的雷達差分測量研究此區域的地表形變，使用的影像為2008-2011年間的Envisat雷達影像與MODIS水汽資料，研究結果顯示此區域的大氣變化大約有0-20百分比且濕延遲結果在平地的影響比山地大，而雷達差分測量利用這兩個方法去除大氣效應之後的結果可明顯的看出地表的形變以及可能因斷層構造的活動變化，最後我們對於大氣效應與雷達差分測量做一個敏感度測試，結果顯示出此影響不是呈線性的，在大氣資料1-2倍時較為影響，到大氣資料3倍時影響則相較少，因此我們知道大氣效應對雷達差分測量會有影響但有一定的限度。;Differential Interferometric Synthetic Aperture RADAR (DInSAR) technique has been successfully used to observe the surface deformation with the high spatial resolution. However, a major limitation for measurement is affected by atmospheric propagation delay due to the significant impact on microwave signals. To solve this problem, some methods have been proposed in the past decade years. (1) DInSAR technique combines the optical images to correct the atmospheric delay caused by water vapor. (2) Persistent Scatterer (PS) InSAR technique, which choose the stable scatterers with time series images, estimate and reduce the effects by processing high-pass filtering in time and low-pass filtering in space. The study area is in the Uttarakhand state of Western Himalaya, India, including the geologocal units of Lesser Himalaya, Siwalik Hills and the Ganga plain, India. Because the lack of reseaches and data, geodesy and seismic data, we applied previous techniques in our study area by using the Envisat and MODIS images during the period from 2008-2011. The difference of MODIS PWV between the date shows 0 – 20 percent change and the zenith wet delay maps shows larger value in plain area than the mountain area. After the process of using optical images, MODIS data, the values of displacement are decreased and the deformation pattern of along the Himalaya area is much more reliable. The PSInSAR result shows detail movement related to the tectonic. Both technique results successfully reveal obvious surface deformation, which may be related to the tectonic activity in the region. Final, the sensitivity test of DInSAR and atmospheric data shows the non-linear changes between the atmospheric data and DInSAR result. The atmosphere delay may affect the DInSAR result, but has upper limit.
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