Taiwan Group on Earth Observations

Hsinchu, Taiwan

Taiwan Group on Earth Observations

Hsinchu, Taiwan
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Liou Y.-A.,National Central University | Liou Y.-A.,Taiwan Group on Earth Observations | Nguyen A.K.,National Central University | Nguyen A.K.,Vietnam Academy of Science and Technology | Li M.-H.,National Central University
Ecological Indicators | Year: 2017

An indicator of quantifying eco-environmental vulnerability was established by synthesizing 12 variables, mainly retrieved from satellite data with incorporation of analytical hierarchy process (AHP). Six vulnerability levels of potential, slight, light, medium, heavy, and very heavy were graded to depict changes of vulnerability over temporal and spatial scales. The proposed approach was employed to study spatiotemporal eco-environmental vulnerability with Landsat data acquired in 1989, 2003, and 2014 for the Thua Thien – Hue Province, Vietnam. Over the time periods of 1989–2003 and 2003–2014, both heavy and very heavy vulnerability levels exhibit an increasing trend in both magnitude and spatial size: The former raised from 5.9% in 1989, to 7.9% in 2003, and 15% in 2014; and the later increased from 1.2% in 1989, to 3.2% in 2003, and 7.3% in 2014. Both levels mainly appeared on urbanized area, bare land, semi-bare land, agricultural land, and sparse forests. In contrast, there was a significant decline in potential vulnerability level with 36.4% in 1989, 30.9% in 2003, and 19.2% in 2014, while the remaining vulnerability levels slight, light, and medium fluctuated slightly, increased in 2003 and decreased in 2014. Supporting reasons for such changes include: (1) deforestation, agriculture intensification, construction of three hydro-electric projects during the period 2003–2014; and (2) significant expansion of urbanized area leading to differences in thermal signatures in urban areas as compared with rural areas. The findings demonstrate that eco-environmental vulnerability is primarily exaggerated by anthropogenic activities through land use/land cover (LULC) changes and further enhanced by natural processes including disasters in the Thua Thien – Hue Province of Vietnam. The correlation between land surface temperature (LST) and Normalized Difference Built-up Index (NDBI) is found to be positively correlated with 0.87, 0.89, and 0.84 for 1989, 2003, and 2014, respectively. In contrast, LST-Normalized Difference Vegetation Index (NDVI) is found negatively correlated with respect to the spatiotemporal trend of environmental vulnerability with −0.81, −0.81, and −0.76 in 1989, 2003, and 2014, respectively. In addition, areas having potential, slight, and medium thermal environmental levels are decreased from 1989 to 2003 to 2003–2014. At the regional scale, increased anthropogenic activities through land's modification have intensified the eco-environmental vulnerability in the study area. The currently proposed methodology is feasible for evaluating long-term eco-environmental changes processes by using remote sensing data, and valid for the other regions. © 2017 Elsevier Ltd

Liou Y.-A.,National Central University | Liou Y.-A.,Taiwan Group on Earth Observations | Liou Y.-A.,Taiwan Geographic Information System Center | Liu H.-L.,Taiwan Group on Earth Observations | And 4 more authors.
Terrestrial, Atmospheric and Oceanic Sciences | Year: 2015

Taiwan has a Subtropic to Tropical climate, but its precipitation varies widely in response to seasonal effects and weather events such as Typhoon and Meiyu systems. Precipitation must be held back in reservoirs to provide and regulate sufficient water supply. Balancing the irregular precipitation and increasing water demands generates tremendous pressure on water resources management for the water stored in the Shihmen Reservoir, which is the major unitary water supply system in the Greater Taoyuan Area. Such pressure will be significantly enlarged due to the huge 17 billion USD Taoyuan Aerotropolis Project. In earlier days many small artificial ponds (a common terminology in this article), including irrigation ponds, fishery ponds and others, were built to cope with water shortages in Taoyuan County. These small storage ponds provided a solution that resolved seasonal precipitation shortages. Unfortunately, these ponds have been vanishing one after another one due to regional industrialization and urbanization in recent decades and less than 40% of them still remain today. There is great urgency and importance to investigating the link between vanishing ponds and water resources management. Remote sensing technology was used in this study to monitor the environmental consequences in the Taoyuan area by conducting multi-temporal analysis on the changes in water bodies, i.e., ponds. SPOT satellite images taken in 1993, 2003, and 2010 were utilized to analyze and assess the importance of small-scale ponds as water conservation facilities. It was found that, during the seventeen years from 1993 - 2010, the number of irrigation ponds decreased by 35.94%. These ponds can reduce the burden on the major reservoir and increase the water recycling rate if they are properly conserved. They can also improve rainfall interception and surface detention capabilities, and provide another planning advantage for regional water management.

Nguyen A.K.,National Central University | Nguyen A.K.,Vietnam Academy of Science and Technology | Liou Y.-A.,National Central University | Liou Y.-A.,Taiwan Group on Earth Observations | And 3 more authors.
Ecological Indicators | Year: 2016

Eco-environmental vulnerability assessment is crucial for environmental and resource management. However, evaluation of eco-environmental vulnerability over large areas is a difficult and complex process because it is affected by many variables including hydro-meteorology, topography, land resources, and human activities. The Thua Thien - Hue Province and its largest river system, the Perfume River, are vital to the social-economic development of the north central coastal region of Vietnam, but there is no zoning system for environmental protection in this region. An assessment framework is proposed to evaluate the vulnerable eco-environment in association with 16 variables with 6 of them constructed from Landsat 8 satellite image products. The remaining variables were extracted from digital maps. Each variable was evaluated and spatially mapped with the aid of an analytical hierarchy process (AHP) and geographical information system (GIS). An eco-environmental vulnerability map is assorted into six vulnerability levels consisting of potential, slight, light, medium, heavy, and very heavy vulnerabilities, representing 14%, 27%, 17%, 26%, 13%, 3% of the study area, respectively. It is found that heavy and very heavy vulnerable areas appear mainly in the low and medium lands where social-economic activities have been developing rapidly. Tiny percentages of medium and heavy vulnerable levels occur in high land areas probably caused by agricultural practices in highlands, slash and burn cultivation and removal of natural forests with new plantation forests. Based on our results, three ecological zones requiring different development and protection solutions are proposed to restore local eco-environment toward sustainable development. The proposed integrated method of remote sensing (RS), GIS, and AHP to evaluate the eco-environmental vulnerability is useful for environmental protection and proper planning for land use and construction in the future. © 2016 Elsevier Ltd. All rights reserved.

Dao P.D.,National Central University | Dao P.D.,Taiwan Group on Earth Observations | Liou Y.-A.,National Central University | Liou Y.-A.,Taiwan Group on Earth Observations
Remote Sensing | Year: 2015

Cambodia is one of the most flood-prone countries in Southeast Asia. It is geographically situated in the downstream region of the Mekong River with a lowland floodplain in the middle, surrounded by plateaus and high mountains. It usually experiences devastating floods induced by an overwhelming concentration of rainfall water over the Tonle Sap Lake's and Mekong River's banks during monsoon seasons. Flood damage assessment in the rice ecosystem plays an important role in this region as local residents rely heavily on agricultural production. This study introduced an object-based approach to flood mapping and affected rice field estimation in central Cambodia. In this approach, image segmentation processing was conducted with optimal scale parameter estimation based on the variation of objects' local variances. The inundated area was identified by using Landsat 8 images with an overall accuracy of higher than 95% compared to those derived from finer spatial resolution images. Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation index products were utilized to identify the paddy rice field based on seasonal inter-variation between vegetation and water index during the transplanting stage. The rice classification result was well correlated with the statistical data at a commune level (R2 = 0.675). The flood mapping and affected rice estimation results are useful to provide local governments with valuable information for flooding mitigation and post-flooding compensation and restoration. © 2015 by the authors.

Kuo Y.-C.,National Taiwan Normal University | Lee M.-A.,National Taiwan Ocean University | Lee M.-A.,Taiwan Group on Earth Observations | Lu M.-M.,Research and Development Center
Atmospheric Research | Year: 2016

The variability of the amount of October rainfall in Taiwan is the highest among all seasons. The October rainfall in Taiwan is attributable to interactions between the northeasterly monsoon and typhoons and their interaction with Taiwan's Central Mountain Range. This study applied long-term gridded rainfall data for defining the major rainfall pattern for October in Taiwan. The empirical orthogonal function Model 1 (80%) of the October rainfall and El Niño Southern Oscillation (ENSO) index exhibited a significant out-of-phase coherence in a 2-4 year period band. This is because an easterly flow on the northern edge of an anomalous low-level cyclonic circulation over the South China Sea during a La Niña developing stage increased the occurrence of an autumn cold front and enhanced the northeasterly monsoon toward northern Taiwan. In addition, a southerly flow on the eastern edge of the anomalous cyclone increased the moisture transport from the tropical Pacific toward Taiwan. The warmer sea surface temperature in the South China Sea, Kuroshio, and the subtropical western Pacific, which may have been induced by an ENSO warm phase peak in the preceding winter, promoted the formation of the anomalous low-level cyclonic circulation. © 2016 Elsevier B.V.

Kuo Y.-C.,National Taiwan Ocean University | Lee M.-A.,National Taiwan Ocean University | Lee M.-A.,Taiwan Group on Earth Observations | Lu M.-M.,Research and Development Center
Advances in Meteorology | Year: 2016

A 50-year (1960-2009) monthly rainfall gridded dataset produced by the Taiwan Climate Change Projection and Information Platform Project was presented in this study. The gridded data (5 × 5 km) displayed influence of topography on spatial variability of rainfall, and the results of the empirical orthogonal functions (EOFs) analysis revealed the patterns associated with the large-scale sea surface temperature variability over Pacific. The first mode (65%) revealed the annual peaks of large rainfall in the southwestern mountainous area, which is associated with southwest monsoons and typhoons during summertime. The second temporal EOF mode (16%) revealed the rainfall variance associated with the monsoon and its interaction with the slopes of the mountain range. This pattern is the major contributor to spatial variance of rainfall in Taiwan, as indicated by the first mode (40%) of spatial variance EOF analysis. The second temporal EOF mode correlated with the El Niño Southern Oscillation (ENSO). In particular, during the autumn of the La Niña years following the strong El Niño years, the time-varying amplitude was substantially greater than that of normal years. The third temporal EOF mode (7%) revealed a north-south out-of-phase rainfall pattern, the slowly evolving variations of which were in phase with the Pacific Decadal Oscillation. Because of Taiwan's geographic location and the effect of local terrestrial structures, climate variability related to ENSO differed markedly from other regions in East Asia. Copyright © 2016 Yi-Chun Kuo et al.

Wu M.-C.,National Cheng Kung University | Yang M.-S.,National Cheng Kung University | Liu H.-C.,National Cheng Kung University | Liu J.-K.,Taiwan Group on Earth Observations
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

LiDAR DEM (Digital Elevation Model) data of two different periods, before and after a heavy rain event, were acquired to specify the exact boundary of the mass been moved, and to calculate the variations of ground elevation by using the DEM values for each photometric cellular element. With the modified Sediment Production Rate (SPR) equation, volumes of the mass wasted were as well being estimated. In addition, with the aids of spatial analysis tools of Geographic Information System (GIS), details of the landslide were well enhanced; such that, the magnitude and the peripheral extent of the landslide were characterized. © 2012 IEEE.

Yang M.-S.,National Cheng Kung University | Wu M.-C.,National Cheng Kung University | Liu J.-K.,Taiwan Group on Earth Observations
Journal of Marine Science and Technology (Taiwan) | Year: 2014

With advancements in the efficiency and accuracy of investigation techniques and equipment, remote sensing technologies have been widely used to investigate river conditions. Quantifying the morphology along a river channel was difficult before airborne laser altimetry technology, light detection and ranging (LiDAR), was introduced, facilitating the collection of high-resolution, highly accurate topographical data. This study adopted airborne LiDAR data for analyzing and recognizing riverbed morphology. The roughness index was defined as the standard deviation of a residual topography. A variable moving-window was used to derive a smoothed digital elevation model (DEM). According to the roughness index, the residual topography was the difference between the original and smoothed DEMs. Roughness data derived from different reaches of a predisaster riverbed were compared with data derived from a postdisaster riverbed. The experimental results showed that the upper reaches exhibited higher roughness values than did the lower reaches. Thus, the relief of the postdisaster riverbed surface was near the derived smoothed relief. Such characteristics were reflected in the major differences evaluated through slope measurements in the riverbed morphological analysis; the position of the peak value changed after the disaster. An integrated plane-wise fluvial circumstance of a river watershed area was rapidly and accurately constructed, and this study concluded that these remote sensing techniques are vital in facilitating traditional surveys for regional investigations.

Lan K.-W.,National Taiwan Ocean University | Lee M.-A.,National Taiwan Ocean University | Lee M.-A.,Taiwan Group On Earth Observations | Zhang C.I.,Pukyong National University | And 4 more authors.
Climatic Change | Year: 2014

Grey mullet (Mugil cephalus L.) is one of the most important commercial species of fish in the coastal fisheries of Taiwan. In this study, we analyzed the long-term (1967–2009) records of grey mullet catch per unit effort (CPUE) in the Taiwan Strait (TS) to investigate the influences of climatic indices on the annual catch of grey mullet at multiple timescales. A wavelet analysis revealed that variations in climatic indices, namely the Pacific Decadal Oscillation (PDO), the Oceanic Niño Index, and sea surface temperatures (SSTs) might have affected the abundance and migration behavior of grey mullet in the TS in winter. The CPUE of grey mullet showed significant high correspondence with the annual PDO index (R2=0.82, p <0.01). The results suggested that the PDO affects the migration of grey mullet, but that increases in SSTs are a more important influence on the decreased catches of grey mullet after 1980. Mean SSTs increased 1.01 °C at the Chang-Yuen Rise in the TS from 1984 to 2009. The 20 °C isotherms in the TS in the winter also shifted from 23–24°N in 1958–1978 to north of 25°N after 1998. The fishing grounds of grey mullet also shifted to the north following changes in the 20 °C isotherm in the TS. © 2014, The Author(s).

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