Browsing by Author "Chang, Yi"

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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.
Non-doped solid-state white light-emitting electrochemical cells employing the microcavity effect
(2015-03-14)
Lin, Guan-Rung
;
Chen, Hsiao-Fan
;
Shih, Hsien-Chang
;
Hsu, Jia-Hong
;
Chang, Yi
Solid-state white light-emitting electrochemical cells (LECs) have attracted research attention owing to their advantages of simple device structure, low operation voltage and compatibility with solution processes. In this work, we demonstrate a simple approach to obtain white electroluminescence (EL) from non-doped LECs based on a blue-emitting complex. With a relatively thicker emissive layer, red emission can be additionally enhanced by the microcavity effect when the recombination zone moves to appropriate positions. Hence, white EL can be harvested by combining blue emission from the complex and red emission from the microcavity effect. These non-doped white LECs show external quantum efficiencies and power efficiencies up to 5% and 12 lm W-1, respectively. These results show that efficient white EL can be obtained in simple non-doped LECs.