Implementation of Digital Photogrammetry for monitoring The Tsaolin Area in Taiwan
Jihn-Fa Jan (Taiwan)
Assistant Professor, Department of Geography
National Changhua University of Education
1, Jinn Der Road, Changhua 500, Taiwan
Telephone: +886-4-7232105 ext. 2825 Facsimile: +886-4-7211186
E-mail: jfjan@cc.ncue.edu.tw
Jih-Cheng RU (Taiwan)
Director
Agricultural and Forestry Aerial Survey Institute
No. 61-3, Chao-Chou Street, Taipei 106, Taiwan
Telephone: +886-2-23931837 Facsimile: +886-2-23931870
E-mail: nn240918@ms19.hinet.net
Yeong-Kuan CHEN (Taiwan)
Professor, Department of Forestry
National Taiwan University
1, Sec. 4, Roosevelt Road, Taipei 106, Taiwan
Telephone: +886-2-23630231 ext. 3134
Facsimile: +886-2-23639799
E-mail: ykchen@ccms.ntu.edu.tw
Key Words
digital photogrammetry, GIS, digital terrain model.
Abstract
On 21 September 1999, an earthquake of 7.3 on the Richter scale shook the Tsaolin area and caused an enormous landslide. Accompanying the quake, a large natural dam was formed by the fallen rocks and debris. Due to the fragile geological structure in this area, effective measures are needed to prevent devastating floods caused by collapse of the dam. The objective of this research was to apply digital photogrammetry to monitor the Tsaolin area so as to provide valuable information for flood prevention, water resource planning, and hydraulic engineering. In this research, aerial photographs obtained after the earthquake were used to investigate the geomorphic status in the study area. The aerial photographs were converted to digital images using high-resolution scanning device. Using the digital images, the digital photogrammetric technique was applied to collect digital terrain model (DTM) grids and other topographic features of the study area. Furthermore, from the digital terrain models, GIS was applied to derive stream networks, watersheds, aspect, slope, curvature, profile curvature, planform curvature, and several physiographic parameters for this area. The results indicate that, digital photogrammetry is an effective approach for monitoring geomorphic status of a large area. In addition, the digital terrain model generated by digital photogrammetry can be readily applied to produce topographic and geomorphic data that are valuable for various disciplines.
1. Introduction
In the past few decades, there were three large landslides in the Tsaolin Area, Yunlin County, Taiwan. On 21 September 1999, an earthquake of 7.3 on the Richter scale shook the area and caused another landslide. Accompanying the quake, a large natural dam was formed by the fallen rocks and debris. Due to the fragile geological structure in this area, effective measures are needed to prevent devastating floods caused by collapse of the dam. Any treatment on the area should be based on accurate estimate of the volume of the dam, amount of water, and flow path. However, the road condition and instability of the slope makes surveying the area very difficult and costly.
Photogrammetry has the advantages of acquiring information about a large area very efficiently and cost effectively. Especially for inaccessible areas, photogrammetry is far more superior than traditional ground survey. In recent years, inexpensive computers and advance of computer technologies contributed to the rapid development of digital photogrammetry (Dowman et al., 1992; Heipke, 1995). Successful implementation of digital photogrammetric workstation in mapping have been found in various disciplines (Chen et al., 1998; Skalet et al., 1992). In this research, aerial photographs obtained after the earthquake were used to investigate the geomorphic status in the study area. The aerial photographs were converted to digital images using high-resolution scanning device. Using the digital images, the digital photogrammetric technique was applied to collect digital terrain model (DTM) grids and other topographic features of the study area. The objective of this research was to apply digital photogrammetry to monitor the Tsaolin area so as to provide valuable information for flood prevention, water resource planning, and hydraulic engineering.
2. Materials and Methods
2.1 Study area
As shown in Figure 1, the study area, Tsaolin, is located in the Gukon Township of Yunlin County. This area is the upstream region of the Chinsuei Creek, and the elevation ranges between 280 m and 1400 m.
Figure 1. Location map of the study area.
2.2 Materials
A set of aerial photographs of the study area was acquired on December 24, 1999. The aerial camera used was a RMK A TOP 15/23 manufactured by Carl Zeiss. The average flight height was 3,000 meters above mean ground elevation, which yielded 1:19,000-1:21,000 for the scale of the photographs. For these photographs, the percentage of forward overlap and side overlap were about 80% and 30%, respectively. The hardware and software used in the study included Zeiss C-130 analytical stereoplotter, digital photogrammetric workstation (Intergraph ImageStation), aerial photograph scanner, personal computers, ArcInfo, ArcView GIS, and MicroStation.
