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Now showing items 1 - 16 of 49

  • Optimal Endmember-Based Super-Resolution Land Cover Mapping

    Li, Xinyan   Li, Xiaodong   Foody, Giles   Yang, Xiaohong   Zhang, Yihang   Du, Yun   Ling, Feng  

    Super-resolution mapping (SRM) aims to determine the spatial distribution of the land cover classes contained in the area represented by mixed pixels to obtain a more appropriate and accurate map at a finer spatial resolution than the input remotely sensed image. The image-based SRM models directly use the observed images as input and can mitigate the uncertainty caused by class fraction errors. However, existing image-based SRM models always adopt a fixed set of endmembers used in the entire image, ignoring the spatial variability and spectral uncertainty of endmembers. To address this problem, this letter proposed an optimal endmember-based SRM (OESRM) model, which considers the spatial variations in endmembers, and determines the best-fit one for each coarse resolution pixel using the spectral angle and the spectral distance as the spectral similarity indexes. A Sentinel-2A and a Landsat-8 multispectral images were used to analyze the performance of OESRM, by comparing with three other SRM methods which adopt a fixed endmember set or multiple endmember sets. The results showed that OESRM generated resultant land cover maps with more spatial detail, and reduced the confusion between land cover classes with similar spectral features. The proposed OESRM model produced the results with the highest overall accuracy in both experiments, showing its effectiveness in reducing the effect of endmember uncertainty on SRM.
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  • Optimal Endmember-Based Super-Resolution Land Cover Mapping

    Li, Xinyan   Li, Xiaodong   Foody, Giles   Yang, Xiaohong   Zhang, Yihang   Du, Yun   Ling, Feng  

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  • Fusion of Landsat 8 OLI and Sentinel-2 MSI Data

    Wang, Qunming   Blackburn, George Alan   Onojeghuo, Alex O.   Dash, Jadunandan   Zhou, Lingquan   Zhang, Yihang   Atkinson, Peter M.  

    Sentinel-2 is a wide-swath and fine spatial resolution satellite imaging mission designed for data continuity and enhancement of the Landsat and other missions. The Sentinel-2 data are freely available at the global scale, and have similar wavelengths and the same geographic coordinate system as the Landsat data, which provides an excellent opportunity to fuse these two types of satellite sensor data together. In this paper, a new approach is presented for the fusion of Landsat 8 Operational Land Imager and Sentinel-2 Multispectral Imager data to coordinate their spatial resolutions for continuous global monitoring. The 30 m spatial resolution Landsat 8 bands are downscaled to 10 m using available 10 m Sentinel-2 bands. To account for the land-cover/land-use (LCLU) changes that may have occurred between the Landsat 8 and Sentinel-2 images, the Landsat 8 panchromatic (PAN) band was also incorporated in the fusion process. The experimental results showed that the proposed approach is effective for fusing Landsat 8 with Sentinel-2 data, and the use of the PAN band can decrease the errors introduced by LCLU changes. By fusion of Landsat 8 and Sentinel-2 data, more frequent observations can be produced for continuous monitoring (this is particularly valuable for areas that can be covered easily by clouds, thereby, contaminating some Landsat or Sentinel-2 observations), and the observations are at a consistent fine spatial resolution of 10 m. The products have great potential for timely monitoring of rapid changes.
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  • Ultrafast pulsed magnetic fields generated by a femtosecond laser

    Zhu, Baojun   Zhang, Zhe   Jiang, Weiman   Wang, Jinguang   Zhu, Changqing   Tan, Junhao   Zhang, Yihang   He, Yuhang   Li, Yifei   Ma, Jinglong   Li, Yutong  

    An ultrafast pulsed magnetic field from a two-loop solenoid is generated by a femtosecond (fs) laser. High temporal resolution is needed to measure the magnetic field. We describe an improved Faraday-rotation measurement to evaluate the evolution of the magnetic field with a resolution of similar to 3.3 picoseconds (ps) in a single shot, with an uncompressed chirped pulse from a Ti:sapphire laser as the optical probe. A magnetic field of 0.52 T with a rise time of 20.8 ps has been measured with this chirped Faraday probe. In addition, we demonstrate the magnetic field strength driven by the femtosecond laser can be modified by adjusting the focal spot size. Published by AIP Publishing.
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  • Combined Variable Speed Limit and Lane Change Control for Highway Traffic

    Zhang, Yihang   Ioannou, Petros A.  

    Variable speed limit (VSL) control of highway traffic is expected to improve traffic mobility, safety, and environment, especially during incidents. However, most existing VSL controllers show significant benefits in macroscopic analysis but little improvement in microscopic simulations in terms of traffic mobility. We demonstrate that the lack of improvement for travel time in many incident cases is due to lane changes that are taking place close to the bottleneck leading to severe capacity drop, which is not adequately captured by most macroscopic models. In this paper, we develop a combined lane change and VSL control scheme, which generates consistent improvements both with macroscopic and microscopic models. The lane change controller generates lane change recommendations upstream the incident or bottleneck in order to reduce the effect of the capacity drop. The VSL controller is developed using a feedback linearization approach based on the cell transmission macroscopic model and is shown analytically to guarantee exponential convergence to the optimum equilibrium point. Microscopic Monte Carlo simulations of traffic on the I-710 freeway were used to demonstrate that this combined control strategy is able to generate consistent improvements with respect to travel time, safety, and environmental impact under different traffic conditions and incident scenarios.
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  • Integrated control of highway traffic flow

    Zhang, Yihang   Ioannou, Petros A.  

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  • Learning-Based Superresolution Land Cover Mapping

    Ling, Feng   Zhang, Yihang   Foody, Giles M.   Li, Xiaodong   Zhang, Xiuhua   Fang, Shiming   Li, Wenbo   Du, Yun  

    Superresolution mapping (SRM) is a technique for generating a fine-spatial-resolution land cover map from coarse-spatial-resolution fraction images estimated by soft classification. The prior model used to describe the fine-spatial-resolution land cover pattern is a key issue in SRM. Here, a novel learning-based SRM algorithm, whose prior model is learned from other available fine-spatial-resolution land cover maps, is proposed. The approach is based on the assumption that the spatial arrangement of the land cover components for mixed pixel patches with similar fractions is often similar. The proposed SRM algorithm produces a learning database that includes a large number of patch pairs for which there is a fine-and coarse-spatial-resolution representation for the same area. From the learning database, patch pairs that have similar coarse-spatial-resolution patches as those in the input fraction images are selected. Fine-spatial-resolution patches in these selected patch pairs are then used to estimate the latent fine-spatial-resolution land cover map by solving an optimization problem. The approach is illustrated by comparison against state-of-the-art SRM methods using land cover map subsets generated from the USA's National Land Cover Database. Results show that the proposed SRM algorithm better maintains the spatial pattern of land covers for a range of different landscapes. The proposed SRM algorithm has the highest overall accuracy and kappa values in all of these SRM algorithms, by using the entire maps in the accuracy assessment.
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  • Optimal number and location planning of evacuation leader in subway stations

    Zhou, Min   Dong, Hairong   Zhao, Yanbo   Zhang, Yihang   Ioannou, Petros A.  

    Evacuation leaders are conducive to the improvement of crowd evacuation efficiency when the evacuees are not familiar with the evacuation routes. The assignment of the number and positions of leaders is particularly important for the efficiency of evacuation. This paper formulates the optimization of passenger evacuation with leaders in a subway station by taking the labor, time, and safety costs into account. A maximal covering model with modifications is proposed to optimize the number and initial locations of leaders. The modifications of social force model are used to represent the dynamics of the evacuees and the leaders in simulations. We use the microscopic simulations of the evacuation of a subway station in Beijing to evaluate the performance of the proposed optimal evacuation strategy. Compared to empirically placing the leaders in the subway station, the proposed strategy shows better performance in terms of labor cost, evacuation time and safety level. (C) 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
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  • Spatial-temporal fraction map fusion with multi-scale remotely sensed images

    Zhang, Yihang   Foody, Giles M.   Ling, Feng   Li, Xiaodong   Ge, Yong   Du, Yun   Atkinson, Peter M.  

    Given the common trade-off between the spatial and temporal resolutions of current satellite sensors, spatial-temporal data fusion methods could be applied to produce fused remotely sensed data with synthetic fine spatial resolution (FR) and high repeat frequency. Such fused data are required to provide a comprehensive understanding of Earth's surface land cover dynamics. In this research, a novel Spatial-Temporal Fraction Map Fusion (STFMF) model is proposed to produce a series of fine-spatial-temporal-resolution land cover fraction maps by fusing coarse-spatial-fine-temporal and fine-spatial-coarse-temporal fraction maps, which may be generated from multi-scale remotely sensed images. The STFMF has two main stages. First, FR fraction change maps are generated using kernel ridge regression. Second, a FR fraction map for the date of prediction is predicted using a temporal-weighted fusion model. In comparison to two established spatial-temporal fusion methods of spatial-temporal super-resolution land cover mapping model and spatial-temporal image reflectance fusion model, STFMF holds the following characteristics and advantages: (1) it takes account of the mixed pixel problem in FR remotely sensed images; (2) it directly uses the fraction maps as input, which could be generated from a range of satellite images or other suitable data sources; (3) it focuses on the estimation of fraction changes happened through time and can predict the land cover change more accurately. Experiments using synthetic multi-scale fraction maps simulated from Google Earth images, as well as synthetic and real MODIS-Landsat images were undertaken to test the performance of the proposed STFMF approach against two benchmark spatial-temporal reflectance fusion methods: the Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model (ESTARFM) and the Flexible Spatiotemporal Data Fusion (FSDAF) model. In both visual and quantitative evaluations, STFMF was able to generate more accurate FR fraction maps and provide more spatial detail than ESTARFM and FSDAF, particularly in areas with substantial land cover changes. STFMF has great potential to produce accurate time-series fraction maps with fine-spatial-temporal-resolution that can support studies of land cover dynamics at the sub-pixel scale.& nbsp;
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  • Spatial-temporal fraction map fusion with multi-scale remotely sensed images

    Zhang, Yihang   Foody, Giles M.   Ling, Feng   Li, Xiaodong   Ge, Yong   Du, Yun   Atkinson, Peter M.  

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  • Combined Variable Speed Limit and Lane Change Control for Highway Traffic

    Zhang, Yihang   Ioannou, Petros A.  

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  • MCU-Controlling Based Bluetooth Data Transferring System

    Liu, Jia   Sun, Guangmin   Zhao, Dequn   Yao, Xu   Zhang, Yihang  

    Based on researching of Bluetooth Protocol, a kind of Bluetooth data transferring system based on MCU-controlling has been proposed in the paper. In the system, the MCU in which the Bluetooth HCI protocol has been embedded is used to control the Bluetooth module on UART and make the Bluetooth devices in the Bluetooth network establish connection and transfer data automatically. In the hardware design, the chip C8051F020 is selected as the host controller. Because chip C8051F020 has two UART serial interfaces, it can meet the requirement of design, simplify the circuit and enhance system anti-jamming capability. The Bluetooth module used in the system is CSR Bluetooth Core 4 with Bluetooth Standard 2.0 class 1 which has the advantages of high signal sensitivity, long distance of connection and easy to use.. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Harbin University of Science and Technology
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  • Example-Based Super-Resolution Land Cover Mapping Using Support Vector Regression

    Zhang, Yihang   Du, Yun   Ling, Feng   Fang, Shiming   Li, Xiaodong  

    Super-resolution mapping (SRM) is a promising technique to generate a fine resolution land cover map from coarse fractional images by predicting the spatial locations of different land cover classes at subpixel scale. In most cases, SRM is accomplished by using the spatial dependence principle, which is a simple method to describe the spatial patterns of different land cover classes. However, the spatial dependence principle used in existing SRM models does not fully reflect the real-world situations, making the resultant fine resolution land cover map often have uncertainty. In this paper, an example-based SRM model using support vector regression (SVR_SRM) was proposed. Without directly using an explicit formulation to describe the prior information about the subpixel spatial pattern, SVR_SRM generates a fine resolution land cover map from coarse fractional images, by learning the nonlinear relationships between the coarse fractional pixels and corresponding labeled subpixels from the selected best-match training data. Based on the experiments of two subset images of National Land Cover Database (NLCD) 2001 and a subset of real hyperspectral Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) image, the performance of SVR_SRM was evaluated by comparing with the traditional pixel-based hard classification (HC) and several existing typical SRM algorithms. The results show that SVR_SRM can generate fine resolution land cover maps with more detailed spatial information and higher accuracy at different spatial scales.
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  • Mapping annual forest cover by fusing PALSAR/PALSAR-2 and MODIS NDVI during 2007-2016

    Zhang, Yihang   Ling, Feng   Foody, Giles M.   Ge, Yong   Boyd, Doreen S.   Li, Xiaodong   Du, Yun   Atkinson, Peter M.  

    Advanced Land Observing Satellite (ALOS) Phased Arrayed L-band Synthetic Aperture Radar (PALSAR) HH and HV polarization data were used previously to produce annual, global 25 m forest maps between 2007 and 2010, and the latest global forest maps of 2015 and 2016 were produced by using the ALOS-2 PALSAR-2 data. However, annual 25 m spatial resolution forest maps during 2011-2014 are missing because of the gap in operation between ALOS and ALOS-2, preventing the construction of a continuous, fine resolution time-series dataset on the world's forests. In contrast, the MODerate Resolution Imaging Spectroradiometer (MODIS) NDVI images were available globally since 2000. This research developed a novel method to produce annual 25 m forest maps during 2007-2016 by fusing the fine spatial resolution, but asynchronous PALSAR/PALSAR-2 with coarse spatial resolution, but synchronous MODIS NDVI data, thus, filling the four-year gap in the ALOS and ALOS-2 time-series, as well as enhancing the existing mapping activity. The method was developed concentrating on two key objectives: 1) producing more accurate 25 m forest maps by integrating PALSAR/PALSAR-2 and MODIS NDVI data during 2007-2010 and 2015-2016; 2) reconstructing annual 25 m forest maps from time-series MODIS NDVI images during 2011-2014. Specifically, a decision tree classification was developed for forest mapping based on both the PALSAR/PALSAR-2 and MODIS NDVI data, and a new spatial-temporal super resolution mapping was proposed to reconstruct the 25 m forest maps from time-series MODIS NDVI images. Three study sites including Paraguay, the USA and Russia were chosen, as they represent the world's three main forest types: tropical forest, temperate broadleaf and mixed forest, and boreal conifer forest, respectively. Compared with traditional methods, the proposed approach produced the most accurate continuous time-series of fine spatial resolution forest maps both visually and quantitatively. For the forest maps during 2007-2010 and 2015-2016, the results had greater overall accuracy values (> 98%) than those of the original JAXA forest product. For the reconstructed 25 m forest maps during 2011-2014, the increases in classifications accuracy relative to three benchmark methods were statistically significant, and the overall accuracy values of the three study sites were almost universally > 92%. The proposed approach, therefore, has great potential to support the production of annual 25 m forest maps by fusing PALSAR/PALSAR-2 and MODIS NDVI during 2007-2016.
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  • Multimillijoule coherent terahertz bursts from picosecond laser-irradiated metal foils

    Liao, Guoqian   Li, Yutong   Liu, Hao   Scott, Graeme G.   Neely, David   Zhang, Yihang   Zhu, Baojun   Zhang, Zhe   Armstrong, Chris   Zemaityte, Egle   Bradford, Philip   Huggard, Peter G.   Rusby, Dean R.   McKenna, Paul   Brenner, Ceri M.   Woolsey, Nigel C.   Wang, Weimin   Sheng, Zhengming   Zhang, Jie  

    Ultrahigh-power terahertz (THz) radiation sources are essential for many applications, for example, THz-wave-based compact accelerators and THz control over matter. However, to date none of the THz sources reported, whether based upon large-scale accelerators or high-power lasers, have produced THz pulses with energies above the millijoule (mJ) level. Here, we report a substantial increase in THz pulse energy, as high as tens of mJ, generated by a high-intensity, picosecond laser pulse irradiating a metal foil. A further up-scaling of THz energy by a factor of similar to 4 is observed when introducing preplasmas at the target-rear side. Experimental measurements and theoretical models identify the dominant THz generation mechanism to be coherent transition radiation, induced by the laser-accelerated energetic electron bunch escaping the target. Observation of THz-field-induced carrier multiplication in high-resistivity silicon is presented as a proof-of-concept application demonstration. Such an extremely high THz energy not only triggers various nonlinear dynamics in matter, but also opens up the research era of relativistic THz optics.
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  • Mapping annual forest cover by fusing PALSAR/PALSAR-2 and MODIS NDVI during 2007–2016

    Zhang, Yihang   Ling, Feng   Foody, Giles M.   Ge, Yong   Boyd, Doreen S.   Li, Xiaodong   Du, Yun   Atkinson, Peter M.  

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