Browsing by Author "Chang, Kuan-Tsung"

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A STATISTICAL ANALYSIS FOR CHARACTERIZING LANDSLIDE CAUSED BY HEAVY RAINFALL AND SEVERE EARTHQUAKE
(2013)
Chang, Kuan-Tsung
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Liu, Jin-King
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Hsu, Wei-Chen
;
Shih, Tian-Yuan
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土木工程學系
Heavy rainfall and earthquakes are the two major factors inducing landslides in Taiwan. The distribution of area size is the most basic quantitative parameter of landslides. Therefore, the purpose of this study is to characterize the scale and spatial difference of rainfall-induced as compared with those of earthquake-induced landslides. Two representative landslide cases, Toraji typhoon occurred in 200 1 and 921 earthquake occurred in 1 999, are used to analyze the causes of different kinds of landslide disasters in the paper. The test area for the 921 earthquake case is 3700 km(2), the recognized number of landslide in the event is 7279, and total area for the landslides is 1 4766 Ha. Moreover, the maximum area of one landslide is 532 Ha, the average area for the landslides is 2 Ha, and its corresponding standard deviation is 1 3 Ha. In the test case of Toraji typhoon, the total study area is 8847 km(2), the number of landslides is 1 0359, and total area for the landslide is 22305 Ha. The maximum area of a landslide is 232 Ha, the average area for the landslides is 2.2 Ha, and its corresponding standard deviation is 6.2 Ha.
ACCURACY EVALUATION OF ALOS DEM WITH AIRBORNE LIDAR DATA IN SOUTHERN TAIWAN
(2015)
Liu, Jin-King
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Chang, Kuan-Tsung
;
Lin, Chinsu
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Chang, Liang-Cheng
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土木工程學系
Recently, some global-scale DEM products, such as GTOPO30, ETOPO1, SRTM and ASTER GDEM have been published for geoscience applications. The latest product, ALOS DEM was announced to be available for a global coverage in 2016. This study examined the performance of ALOS-DEM in describing accurate morphometric and volumetric measurement of land features. A comparison was made on basis of DEM and DSM data of airborne fullwaveform LiDAR data. Results showed that ALOS DEM is more approximately in reality an ALOS DSM which reveals the ground envelop surface rather than the ground bare surface. The differences between ALOS DEM and LiDAR DSM are mainly from 0 to 2.75 m with a standard deviation of 1.58 m. The differences between ALOS DEM and LiDAR DEM give a bias of as large as 20m, mostly located at the areas with abrupt change of relief and mainly in the northfacing slopes. This is probably due to ALOS sensor\'s geometry in corresponding to its looking-direction. The stream networks derived from both ALOS DEM and LiDAR DEM are in good agreement. It is suggested that further studies on methods for assessing geomorphometric changes in landform structures should be developed and compared.
Land Cover Classification Accuracy Assessment Using Full-Waveform LiDAR Data
(2015-04-01)
Chang, Kuan-Tsung
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Yu, Feng-Chi
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Chang, Yi
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Hwang, Jin-Tsong
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Liu, Jin-King
The geomorphology of Taiwan is characterized by marked changes in terrain, geological fractures, and frequent natural disasters. Because of sustained economic growth, urbanization and land development, the land cover in Taiwan has undergone frequent use changes. Among the various technologies for monitoring changes in land cover, remote sensing technologies, such as LiDAR, are efficient tools for collecting a broad range of spectral and spatial data. Two types of airborne LiDAR systems exist; full-waveform (FW) LiDAR and traditional discrete-echo LiDAR. Because reflected waveforms are affected by the land object material type and properties, the waveform features can be applied to analyze the characteristics specifically associated with land-cover classification (LCC). Five types of land cover that characterize the volcanic Guishan Island were investigated. The automatic LCC method was used to elucidate the spectral, geomorphometric and textural characteristics. Interpretation keys accompanied by additional information were extracted from the FW LiDAR data for subsequent statistical and separation analyses. The results show that the Gabor texture and geomorphometric features, such as the normalized digital surface model (nDSM) and slopes can enhance the overall LCC accuracy to higher than 90%. Moreover, both the producer and user accuracy can be higher than 92% for forest and built-up types using amplitude and pulse width. Although the waveform characteristics did not perform as well as anticipated due to the waveform data sampling rate, the data provides suitable training samples for testing the waveform feature effects.
Observing Land Subsidence and Revealing the Factors That Influence It Using a Multi-Sensor Approach in Yunlin County, Taiwan
(2015-06-01)
Hsu, Wei-Chen
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Chang, Hung-Cheng
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Chang, Kuan-Tsung
;
Lin, En-Kai
;
Liu, Jin-King
Land subsidence is a worldwide problem that is typically caused by human activities, primarily the removal of groundwater. In Western Taiwan, groundwater has been pumped for industrial, residential, agricultural, and aquacultural uses for over 40 years. In this study, a multisensor monitoring system comprising GPS stations, leveling surveys, monitoring wells, and Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) was employed to monitor land subsidence in Western Taiwan. The results indicate that land subsidence in Yunlin County was mainly affected by the compaction of subsurface soils and over-pumping of groundwater from deep soils. The study area comprised western foothills, characterized by sediments containing predominantly gravel, and coastal areas, where clay was predominant. The subsidence in coastal areas was more severe than that in the western foothills, as a result of groundwater removal. An additional factor affecting subsidence was the compaction of deep layers caused by deep groundwater removal and the deep-layer compaction was difficult to recover. Based on multisensor monitoring results, severe subsidence is mainly affected by compaction of subsurface soils, over-pumping of groundwater from deep soils, and deep soil compaction.
River Width Measurement Using Sentinel-1 Satellite Data
(2018-01-01)
Hsu, Wei-Ling
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Chang, Kuan-Tsung
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Chang, Liang-Cheng
;
Wang, Chih-Tien
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土木工程學系
The sentinel-1 Synthetic Aperture Radar image analysis technology is conducted to measure river width in a multitemporal change in this study. With the field surveying work, two Sentinel-1A images taken on March 14 and May 24, 2018, have been obtained. Next the SNAP data processing software can be used to produce backscattering coefficient, and the values can be converted into intensity image. Low intensity features related with water body will be helpful for river width measurement. Moreover, an UAS flight also arranged on May 24 to take 525 photos with a DJI Phantom 4 Pro UAS under flying altitude of 120 meters. The Agisoft Photoscan Professional software used to produce an ortho-mosaic image in a spatial resolution of 3.39 cm for the comparison of geometrical differences in river width measurement. According to the comparison results with manual measurement, the derived difference of river width is 1.2 meters at the Zhongtou bridge in the Wuxi river.