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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.

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.

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.

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.

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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