Landsat satellite images were used to map and monitor the snow-covered areas of four glaciers with different aspects(Passu: 36.473°N, 74.766°E;Momhil: 36.394°N, 75.085°E; Trivor: 36.249°N,74.9...Landsat satellite images were used to map and monitor the snow-covered areas of four glaciers with different aspects(Passu: 36.473°N, 74.766°E;Momhil: 36.394°N, 75.085°E; Trivor: 36.249°N,74.968°E; and Kunyang: 36.083°N, 75.288°E) in the upper Indus basin, northern Pakistan, from 1990-2014. The snow-covered areas of the selected glaciers were identified and classified using supervised and rule-based image analysis techniques in three different seasons. Accuracy assessment of the classified images indicated that the supervised classification technique performed slightly better than the rule-based technique. Snow-covered areas on the selected glaciers were generally reduced during the study period but at different rates. Glaciers reached maximum areal snow coverage in winter and premonsoon seasons and minimum areal snow coverage in monsoon seasons, with the lowest snow-covered area occurring in August and September. The snowcovered area on Passu glacier decreased by 24.50%,3.15% and 11.25% in the pre-monsoon, monsoon and post-monsoon seasons, respectively. Similarly, the other three glaciers showed notable decreases in snow-covered area during the pre-and post-monsoon seasons; however, no clear changes were observed during monsoon seasons. During pre-monsoon seasons, the eastward-facing glacier lost comparatively more snow-covered area than the westward-facing glacier. The average seasonal glacier surface temperature calculated from the Landsat thermal band showed negative correlations of-0.67,-0.89,-0.75 and-0.77 with the average seasonal snowcovered areas of the Passu, Momhil, Trivor and Kunyang glaciers, respectively, during pre-monsoon seasons. Similarly, the air temperature collected from a nearby meteorological station showed an increasing trend, indicating that the snow-covered area reduction in the region was largely due to climate warming.展开更多
The geometry of a landslide dam is an important component of evaluating dam stability.However,the geometry of a natural dam commonly cannot be obtained immediately with field investigations due to their remote locatio...The geometry of a landslide dam is an important component of evaluating dam stability.However,the geometry of a natural dam commonly cannot be obtained immediately with field investigations due to their remote locations.A rapid evaluation model is presented to estimate the geometries of natural dams based on the slope of the stream,volume of landslides,and the properties of the deposit.The proposed model uses high resolution satellite images to determine the geometry of the landside dam.These satellite images are the basic information to a preliminary stability analysis of a natural dam.This study applies the proposed method to two case studies in Taiwan.One is the earthquakeinduced Lung-Chung landslide dam in Taitung,and the second is the rainfall-induced Shih-Wun landslide dam in Pingtung.展开更多
The spatial distribution and characterization of a heavily damaged area can be determined by studying surface ruptures of seismogenic faults.If the distribution of surface ruptures can be obtained shortly after they o...The spatial distribution and characterization of a heavily damaged area can be determined by studying surface ruptures of seismogenic faults.If the distribution of surface ruptures can be obtained shortly after they occur,then areas heavily damaged by an earthquake can be readily identified.The information can then be used as a guide for earthquake relief programs.In this paper,an intensity offset-tracking method applied to an ALOS PALSAR image is used to map the Yushu earthquake rupture and to identify the faults activated by the earthquake.Azimuthal displacement analysis indicates that the surface rupture is about 55 km long,running from the epicenter to the southeast,trending N310°W,with a relative displacement of～1 m characterized by sinistral slip.The result of range displacement observations indicates that the north wall of the fault is dominated by decreases(i.e.,uplift in line of sight observations) ,whereas in the south wall of the fault,the range displacement is dominated by increases(drops in line of sight observations) .Given the position from which the images were recorded,this means that the north wall moves westward,and the south wall move eastward,i.e.,left-lateral slip motion across the fault.Finally,an earthquake disaster assessment using computer-assisted image analysis software shows that buildings near the fault rupture have been destroyed most heavily;therefore,the shape of the heavily damage belt is controlled partially by the fault rupture's geometry and the damage degree relates to the magnitude of displacement field.展开更多
基金funded by National Natural Science Foundation of China (41421061, 41630754)Chinese Academy of Sciences (KJZD-EW-G03-04)the State Key Laboratory of Cryospheric Science(SKLCS-ZZ-2017)
文摘Landsat satellite images were used to map and monitor the snow-covered areas of four glaciers with different aspects(Passu: 36.473°N, 74.766°E;Momhil: 36.394°N, 75.085°E; Trivor: 36.249°N,74.968°E; and Kunyang: 36.083°N, 75.288°E) in the upper Indus basin, northern Pakistan, from 1990-2014. The snow-covered areas of the selected glaciers were identified and classified using supervised and rule-based image analysis techniques in three different seasons. Accuracy assessment of the classified images indicated that the supervised classification technique performed slightly better than the rule-based technique. Snow-covered areas on the selected glaciers were generally reduced during the study period but at different rates. Glaciers reached maximum areal snow coverage in winter and premonsoon seasons and minimum areal snow coverage in monsoon seasons, with the lowest snow-covered area occurring in August and September. The snowcovered area on Passu glacier decreased by 24.50%,3.15% and 11.25% in the pre-monsoon, monsoon and post-monsoon seasons, respectively. Similarly, the other three glaciers showed notable decreases in snow-covered area during the pre-and post-monsoon seasons; however, no clear changes were observed during monsoon seasons. During pre-monsoon seasons, the eastward-facing glacier lost comparatively more snow-covered area than the westward-facing glacier. The average seasonal glacier surface temperature calculated from the Landsat thermal band showed negative correlations of-0.67,-0.89,-0.75 and-0.77 with the average seasonal snowcovered areas of the Passu, Momhil, Trivor and Kunyang glaciers, respectively, during pre-monsoon seasons. Similarly, the air temperature collected from a nearby meteorological station showed an increasing trend, indicating that the snow-covered area reduction in the region was largely due to climate warming.
基金supported by National Science Council,Taiwan,China.The project name is Numerical Approach to Estimate the Stability and Deformation Response of Landslide Dams(NSC99-2625-M-006-004)and Modeling of The Compound Disaster in Hsiaolin Village(NSC99-2218-E-006-238)
文摘The geometry of a landslide dam is an important component of evaluating dam stability.However,the geometry of a natural dam commonly cannot be obtained immediately with field investigations due to their remote locations.A rapid evaluation model is presented to estimate the geometries of natural dams based on the slope of the stream,volume of landslides,and the properties of the deposit.The proposed model uses high resolution satellite images to determine the geometry of the landside dam.These satellite images are the basic information to a preliminary stability analysis of a natural dam.This study applies the proposed method to two case studies in Taiwan.One is the earthquakeinduced Lung-Chung landslide dam in Taitung,and the second is the rainfall-induced Shih-Wun landslide dam in Pingtung.
基金supported by National Science and Technology Pillar Program(Grant Nos.2008BAC38B03 and 2008BAC35B04)National Natural Science Foundation of China(Grant Nos.40940020 and 40874006)the Earthquake Research Special Fund(Grant No. 200708013)
文摘The spatial distribution and characterization of a heavily damaged area can be determined by studying surface ruptures of seismogenic faults.If the distribution of surface ruptures can be obtained shortly after they occur,then areas heavily damaged by an earthquake can be readily identified.The information can then be used as a guide for earthquake relief programs.In this paper,an intensity offset-tracking method applied to an ALOS PALSAR image is used to map the Yushu earthquake rupture and to identify the faults activated by the earthquake.Azimuthal displacement analysis indicates that the surface rupture is about 55 km long,running from the epicenter to the southeast,trending N310°W,with a relative displacement of～1 m characterized by sinistral slip.The result of range displacement observations indicates that the north wall of the fault is dominated by decreases(i.e.,uplift in line of sight observations) ,whereas in the south wall of the fault,the range displacement is dominated by increases(drops in line of sight observations) .Given the position from which the images were recorded,this means that the north wall moves westward,and the south wall move eastward,i.e.,left-lateral slip motion across the fault.Finally,an earthquake disaster assessment using computer-assisted image analysis software shows that buildings near the fault rupture have been destroyed most heavily;therefore,the shape of the heavily damage belt is controlled partially by the fault rupture's geometry and the damage degree relates to the magnitude of displacement field.
