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Byun Y.,Core Technology Research Laboratory | Han Y.,Fondazione Bruno Kessler | Chae T.,Korea Aerospace Research Institute
Remote Sensing

Change detection based on satellite images acquired from an area at different dates is of widespread interest, according to the increasing number of flood-related disasters. The images help to generate products that support emergency response and flood management at a global scale. In this paper, a novel unsupervised change detection approach based on image fusion is introduced. The approach aims to extract the reliable flood extent from very high-resolution (VHR) bi-temporal images. The method takes an advantage of the spectral distortion that occurs during image fusion process to detect the change areas by flood. To this end, a change candidate image is extracted from the fused image generated with bi-temporal images by considering a local spectral distortion. This can be done by employing a universal image quality index (UIQI), which is a measure for local evaluation of spectral distortion. The decision threshold for the determination of changed pixels is set by applying a probability mixture model to the change candidate image based on expectation maximization (EM) algorithm. We used bi-temporal KOMPSAT-2 satellite images to detect the flooded area in the city of N'djamena in Chad. The performance of the proposed method was visually and quantitatively compared with existing change detection methods. The results showed that the proposed method achieved an overall accuracy (OA = 75.04) close to that of the support vector machine (SVM)-based supervised change detection method. Moreover, the proposed method showed a better performance in differentiating the flooded area and the permanent water body compared to the existing change detection methods. © 2015 by the authors; licensee MDPI, Basel, Switzerland. Source

Lee S.-J.,Core Technology Research Laboratory | Hwang C.-S.,Core Technology Research Laboratory | Pi J.-E.,Core Technology Research Laboratory | Yang J.-H.,Core Technology Research Laboratory | And 4 more authors.
ETRI Journal

Multilayered ZnO-SnO2 heterostructure thin films consisting of ZnO and SnO2 layers are produced by alternating the pulsed laser ablation of ZnO and SnO2 targets, and their structural and field-effect electronic transport properties are investigated as a function of the thickness of the ZnO and SnO2 layers. The performance parameters of amorphous multilayered ZnO-SnO2 heterostructure thin-film transistors (TFTs) are highly dependent on the thickness of the ZnO and SnO2 layers. A highest electron mobility of 43 cm2/V•s, a low subthreshold swing of a 0.22 V/dec, a threshold voltage of 1 V, and a high drain current on-to-off ratio of 1010 are obtained for the amorphous multilayered ZnO(1.5 nm)- SnO2(1.5 nm) heterostructure TFTs, which is adequate for the operation of next-generation microelectronic devices. These results are presumed to be due to the unique electronic structure of amorphous multilayered ZnOSnO2 heterostructure film consisting of ZnO, SnO2, and ZnO-SnO2 interface layers. © 2015 ETRI. Source

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