時空資訊為將真實世界的空間資訊加上時間尺度，成為一個整合的面向(范毅軍，2006)，隨著測量及航遙測科技的發展，可以定期定時的觀測同一區域，以獲得多時序的觀測資料。以資料而言，衛星影像能涵蓋大範圍的地物，且資料獲取本身即隨衛星運轉而具週期性，對於需要時間序列的應用，衛星影像即是不錯的選擇，而另一常用之資料即為航照影像，航照影像其解析度較高，且發展較衛星影像早，因此較有機會獲取更早期之資料來進行分析。而另一重要之資料為早期所測繪之地形圖(如台灣堡圖)，其對於早期的地形亦提供相當重要的資訊來源。
以多時期的航照資料來進行時空的資訊分析，其歷年航照影像可經過空三的解算還原當年地表資訊在物空間坐標系統下之狀態，並且用以獲得多時期之數值地形模型(DEM)及影像正射化與鑲嵌之產品。
The integration of data in the spatial domain and time domain then has the advantages for the use in many aspects. (Fan, 2006). Thanks to the development of photogrammetry and remote sensing technology, we now can obtain the sensed data on the same region periodically, that is the spatial and temporal data of an interested area can be easily acquired An appropriate remote sensing source for time-series applications comes from satellite images which can routinely operate and cover a very wide region of the landscape. Another common datasets for time-series use is aerial images. The aerial image features earlier than satellite images, and it also has higher resolution rather than satellite images. Therefore, it is more likely to trace the images in the early stage. The other important datasets are topographic maps which were made in very early stage. This kind of map (such as Taiwan Baotu, the first fine topographic map) provides very important information of the topography linking to the human activities at that time.
The time-series aerial images can be used to generate multi-temporal DEMs, ortho-images and mosaic images through a computation process of aerial triangulation.
一、多時期之數值地形模型(DEM)之應用
DEM為不包含地表植被及人工構造物，僅單純紀錄地球表面自然地貌起伏之數值高程模型；而多時序的DEM資料是指不同時期所製作完成的數值高程模型，藉由不同時期之DEM可觀察自然地表隨著時間的不同之起伏情形，用以觀察大範圍區域之地表高程變化趨勢，圖一以雲林縣區域地表之變化行為為例，探討地層下陷的歷史變化。
1. The application of multi-temporal digital terrain model (DEM)
DEM (digital terrain model) describes the Earth's bare surface excluding vegetation or artificial structures above the ground. Multi-DEMs are digital terrain models produced from different periods. We can observe the trend of terrain deformation or the change of land use/cover in a large area by multi-temporal DEMs. Figure 1 shows an example that using multi-temporal aerial images to generate multi-temporal DEMs for retrieving the history of land subsidence.
圖一、四期DEM資料
Figure 1 Multi-temporal DEMs datasets in four years.
二、多時期歷史航照影像正射化與鑲嵌之應用
多時期歷史航照影像透過對位後即可展示於時空資訊平台，將現代正射影像與歷史航照影像以及古地圖對位至同一坐標系統為基礎，可以以時間為主軸，透過一個網路為基礎之同步多視窗進行瀏覽，並能針對同一區域、不同時期的影像做同步瀏覽，以了解一區域內的變遷情形，圖二為成功大學之校區於四時期之歷史變遷。
2. The application of the multi-temporal historical aerial images
Multi-temporal historical aerial images can be displayed through a multi-temporal viewing in GIS after image registration and rectification corresponding to the ground coordinates system. It is a time-based concept, we can browse this map viewer synchronous at the same time within a covered region in different periods to realize and analyze the temporal changes. Figure 2 shows the historical changes of National Cheng Kung University in four different periods.
圖二 多時期視窗瀏覽
Figure2. Multi-temporal datasets in four different periods of the same region.
參考文獻 (References) :
范毅軍，2006， 走進時光隧道：GIS與時空資訊的整合，中央研究院2006年八月知識饗宴。
Fan, I.C., 2006, Time Tunnel: The Integration of GIS and Spatial and Temporal Information, Academia Sinica Knowledge feast in August 2006.
林筱芸，2008，利用多時期航拍影像探討地層下陷歷史變化，國立成功大學測量及空間資訊學系碩士論文。
Lin, H.U., 2008, Retrieving the History of Land Subsidence Using Multi-temporal Aerial Images, Department of Geomatics, National Cheng Kung University, Master Thesis.