地形劇烈變化河道之沖蝕特性及其對河道穩定性的影響及治理策略-子計畫:地形變異時序量測(I)

Abstract

地形地貌之時序變異，可由各個時期之數值地形模型相互比對，達成量化之分析。而 各個歷史時期之地形模型，除由既存之地形測量成果直接取用外，亦可由歷史性影像 產生。在台灣地區，以農林航空測量所歷年來建置之航空攝影相片資料庫，提供最為 豐富之影像資源。而由航空影像產製數值地形模型，目前效率最高之方式為在進行空 中三角之後，以影像匹配方式產出。如欲達成提升數值地形模型相互比對精度，可綜 合為兩個面向：其一為提升各個時期數值地形模型產製精度，包含空中三角與影像匹 配兩個階段；其二為改善比對之方法，由地形之紋理提供所需精化差值數值地形模型 之精度提升。就第一項而言，本期之數值地形模型產製，將擴大相片涵蓋。當片數增 加時，所需之控制點數並不會線性增加。但是將有更佳之機會選取到適當點位。同時， 本子計畫擬整合歷年相同區域影像統合平差，並探討交叉匹配之成果處理，探討整合 性多時期影像同步平差之可行性。就差值數值地形模型(Difference of Digital Elevation Model)之產製而言，若應用地形上地貌特徵，可以類似影像匹配之方式近一步消除各 自空間定位時之基準誤差。適當之地貌分析因子與方式，亦將有對比對精度有所提升。

The geomorphic change of topography could be observed from the digital elevation model of each period. Differencing the DEM of two epochs, the change could be quantitatively analyzed. The digital elevation model of past, unless already produced, it could be generated with historic images, particularly those obtained with aerial mapping camera. In Taiwan, the aerial photo database established by Aerial Survey Office, Forest Bureau, provides the most informative source. The currently most adopted method for producing DEM from aerial photos, is to perform aerial triangulation first, then followed by automated image matching. There are two major ways to improve the quality while comparing the DEM of two epochs. The first is to improve the quality of DEM production. The other is to improve the way two DEMs are compared. Adding more photos to the current block to ease the selection of GCPs, would be the easiest one for the first goal. While the number of photo increases, the requirement of control points does not increase linearly. But, one would have better opportunity for selecting quality GCPs with larger image block. It also could be improved by an adjustment together with all images. Regarding Difference of Digital Elevation Model production, image matching schemes similar to those applied in aerial triangulation could be applied. Besides, the analysis scheme with proper geomorphic parameter sets could provide further improvement.