Browsing by Author "Liu, Jin-King"

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A GEOMORPHOLOGICAL MODEL FOR LANDSLIDE DETECTION USING AIRBORNE LIDAR DATA
(2012-12-01)
Liu, Jin-King
;
Hsiao, Kuo-Hsin
;
Shih, Peter Tian-Yuan
;
土木工程學系
;
Department of Civil Engineering
This study analyzes multi-temporal LiDAR data of high accuracy and high resolution by installing a geomorphometric model for extracting landslides. First, two sets of LiDAR data were acquired for before and after a heavy rainfall event. The landslides which took place from 2005 to 2009 were classified automatically by satellite images, and subsequently the landslides were interpreted and edited manually. Geomorphometric parameters including slope, curvature, OHM, OHM roughness, and topographic wetness index were then extracted using stencils of landslide polygons overlaid on respective thematic maps derived from LiDAR, DEM and DSM. The ranges of every parameter were derived from the statistics of the landslide area. Some selected non-morphometric parameters were also included in a later stage to account for all possible features of landslides, such as vegetation index and geological strength. The ranges of the parameters of landslides were optimized for the model by the statistics of the landslide area. The overall accuracy predicted by the model was 64.9%. When the buffer zones of old landslides and riverside areas were included, the overall accuracy was 64.4%, showing no improvement. When landslides smaller than 50 m(2) were filtered, the 2009, respectively. The results show that the geomorphological model proposed in this research is effective for landslide extraction.
A STATISTICAL ANALYSIS FOR CHARACTERIZING LANDSLIDE CAUSED BY HEAVY RAINFALL AND SEVERE EARTHQUAKE
(2013)
Chang, Kuan-Tsung
;
Liu, Jin-King
;
Hsu, Wei-Chen
;
Shih, Tian-Yuan
;
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.
A Study on Factors Affecting Airborne LiDAR Penetration
(2015-04-01)
Hsu, Wei-Chen
;
Shih, Peter Tian-Yuan
;
Chang, Hung-Cheng
;
Liu, Jin-King
;
土木工程學系
This study uses data from different periods, areas and parameters of airborne LiDAR (light detection and ranging) surveys to understand the factors that influence airborne LiDAR penetration rate. A discussion is presented on the relationships between these factors and LiDAR penetration rate. The results show that the flight height above ground level (AGL) does not have any relationship with the penetration rate. There are some factors that should have larger influence. For example, the laser is affected by a wet ground surface by reducing the number of return echoes. The field of view (FOV) has a slightly negative correlation with the penetration rate, which indicates that the laser incidence angle close to zero should achieve the best penetration. The vegetation cover rate also shows a negative correlation with the penetration rate, thus bare ground and reduced vegetation in the aftermath of a typhoon also cause high penetration rate. More return echoes could be extracted from the full-waveform system, thereby effectively improving the penetration rate. This study shows that full-waveform LiDAR is an effective method for increasing the number of surface reflected echoes. This study suggests avoiding LiDAR survey employment directly following precipitation to prevent laser echo reduction.
ACCURACY EVALUATION OF ALOS DEM WITH AIRBORNE LIDAR DATA IN SOUTHERN TAIWAN
(2015)
Liu, Jin-King
;
Chang, Kuan-Tsung
;
Lin, Chinsu
;
Chang, Liang-Cheng
;
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
;
Yu, Feng-Chi
;
Chang, Yi
;
Hwang, Jin-Tsong
;
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.
LANDSLIDE DETECTION BY INDICES OF LIDAR POINT-CLOUD DENSITY
(2010)
Liu, Jin-King
;
Hsu, Wei-Chen
;
Yang, Mon-Shieh
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Shieh, Yu-Chung
;
Shih, Tian-Yuan
The deliverables of an airborne LiDAR survey usually include all points, ground points, digital surface models (DSM) and digital elevation models (DEM). Indices of point clouds tested in this study include density of all points, density of ground points, density of only returns, and density of multiple returns. Shallow landslides are the most common landslides triggered by torrential rainfalls and explicit fresh scars after rainfall events. Multiple returns in forest area give the possibility of differentiating landslide scars from vegetated lands. Classification results from the indices derived from these four kinds of densities are verified by the result obtained by manual interpretation of the derived nDSM images. The experiment is carried out using the dataset obtained in I-Lan County after Typhoon Kalmaegi on 17 July 2008. The results show that a proper definition of the parameters for the indices is most critical for the detection of shallow landslides.
Lidar DEM for characterizing the volcanic landforms of Tatun Volcanoes in Metropolitan Taipei
(2007)
Liu, Jin-King
;
Chan, Yu-Chang
;
Shih, Tian-Yuan
;
Hsieh, Yu-Chung
;
土木工程學系
Tatun Volcano Group is a cluster of dormant volcanoes surrounding Metropolitan Taipei. Rugged terrain, monotonic lithology and dense vegetation covers are adverse factors for mapping the geological structures. In this study, airborne Lidar survey was conducted to obtain a bare ground DEM with 2m grid and with an accuracy of decimeters. Shaded-relief images, pit-patterns and drainage networks are then derived from these DEMs for visual interpretation. 51 volcanoes are thus recognized. Two fissures running through the highest volcano in this area, namely Mount Seven-stars, are extending 2000m and 1000m, respectively. The largest width and depth of the opening of the ruptures is located in the west flank of the volcanic cone. The slope angle of the cast-wing of the volcanic cone is 36 degrees, whereas the angle of the west-wing is only 24.5 degrees. The opening of the west fissure is larger and its extension is longer than the east one. Thus, the west side can be subjected to an active extensional process of strain. The fissures could be resulted from the ongoing regional extension of the Tatun Volcanic area due to the plate subduction and collision of the Eurasian Plate and the Philippine Sea Plate.
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
;
Chang, Hung-Cheng
;
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.
Topographic Correction of Wind-Driven Rainfall for Landslide Analysis in Central Taiwan with Validation from Aerial and Satellite Optical Images
(2013-06-01)
Liu, Jin-King
;
Shih, Peter T. Y.
;
土木工程學系
;
Department of Civil Engineering
Rainfall intensity plays an important role in landslide prediction especially in mountain areas. However, the rainfall intensity of a location is usually interpolated from rainfall recorded at nearby gauges without considering any possible effects of topographic slopes. In order to obtain reliable rainfall intensity for disaster mitigation, this study proposes a rainfall-vector projection method for topographic-corrected rainfall. The topographic-corrected rainfall is derived from wind speed, terminal velocity of raindrops, and topographical factors from digital terrain model. In addition, scatter plot was used to present landslide distribution with two triggering factors and kernel density analysis is adopted to enhance the perception of the distribution. Numerical analysis is conducted for a historic event, typhoon Mindulle, which occurred in 2004, in a location in central Taiwan. The largest correction reaches 11%, which indicates that topographic correction is significant. The corrected rainfall distribution is then applied to the analysis of landslide triggering factors. The result with corrected rainfall distribution provides better agreement with the actual landslide occurrence than the result without correction.