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Ke W.,Nanjing Normal University | Ke W.,Jiangsu Center for Collaborative Innovation | Yuan Y.,Nanjing Normal University | Zhang X.,Nanjing Normal University | Shao J.,Nanjing Normal University
Progress In Electromagnetics Research M

As an emerging wireless localization technique, the electromagnetic passive localization without the need of carrying any device, named device-free passive localization (DFPL) technique has drawn considerable research attention. The DFPL technique detects shadowed links in the monitored area and realizes localization with the received signal strength (RSS) measurements of these links. However, the current RSS-based DFPL techniques have two major challenges: one is that the RSS signal is particularly sensitive to noise, and the other is that it needs a sufficient number of nodes to provide enough RSS measurements of wireless links to guarantee good performance. To overcome these problems, in this paper we take advantage of compressive sensing (CS) theory to handle the spatial sparsity of the DFPL problem for reducing the number of nodes required by DFPL systems and exploit the frequency diversity technique to deal with the problem of the RSS sensitivity. Meanwhile, inspired by the fact that the target's movement is continuous and that the target's current location must be around the last location, we add prior information on the support region into the sparse reconstruction process for enhancing sparse reconstruction performance. The effectiveness and robustness of the proposed scheme are demonstrated by experimental results where the proposed algorithm yields substantial improvement for localization performance. © 2016, Electromagnetics Academy. All rights reserved. Source

Pei T.,Chinese Academy of Sciences | Pei T.,Jiangsu Center for Collaborative Innovation | Sobolevsky S.,MIT Senseable City Laboratory | Ratti C.,MIT Senseable City Laboratory | And 2 more authors.
Transactions in GIS

The aggregated mobile phone network (AMPN) (i.e. the calling time or numbers are aggregated at every vertex), which records the call volume between different places over time, has been studied extensively to reveal the mobility patterns of residents, etc. Nevertheless, most previous works were implemented based on the non-directionality of the network model. This simplification may overlook some important characteristics of AMPN. To explore the AMPN as a directional network model, we introduce the concept of directional heterogeneity in the study of AMPN data. The heterogeneity is twofold: (1) the imbalance of vertex (difference between outgoing and incoming calls of the vertex); and (2) the reciprocity of each edge (difference between the directed weights of the same edge). Taking the data of Singapore as an example, we systematically analyze the directional heterogeneity of AMPN. Our findings include three aspects. First, the AMPN shows as more unbalanced in the night-time than in the daytime, and its imbalance decreases as vertex granularity increases. Second, the directional heterogeneity varied with locations. Specifically, the residential area is dominated by deficits and others by surpluses. Third, the trajectories of incoming and outgoing calls follow a similar geographical pattern (i.e. southeast-north-south-north-southeast), indicating the calling behavior and routine mobility of users over time and space. © 2014 John Wiley & Sons Ltd. Source

Zhang S.,Nanjing University | Liu Y.,Nanjing University | Liu Y.,Jiangsu Center for Collaborative Innovation | Yang Y.,Nanjing University | And 2 more authors.
Journal of Great Lakes Research

Poyang Lake, an important wetland in the Ramsar Convention List, is the largest freshwater lake in China and an essential component of the Yangtze River system. The lake is increasingly experiencing serious water crises including seasonal desiccation, decreased wetland area, and water shortages, all of which are closely related to progressive changes in the lake's topography over recent years. Atime-series of bottom topography would contribute to our understanding of the lake's evolution during the past several decades. However, quality bathymetric data for Poyang Lake are scarce owing to the highly dynamic and turbid nature of its water. To resolve this limitation, we used a total of 146 medium-resolution satellite images to build annual and quasi-annual bottom topography maps of Poyang Lake during the period from 2000 to 2010 based on the well-established waterline method. Our results show that: (1)the average elevation of the lakebed relative to sea level has decreased by 14.4 cm/yr. from 2000 to 2010; and (2)the observed annual changes in the lakebed elevation were well correlated (r = 0.84) with measured changes in the lake's annual net sediment flux. The observed trends may be attributed to the impacts of human activities, especially the operation of the Three Gorge Dams, frequent sand mining, and the implementation of a large water conservancy project. This decade-long quantitative understanding of the lake's evolution and bottom topography elevations might assist both researchers and local policymakers in ecological management, wetland protection, and lake navigation safety. © 2016 International Association for Great Lakes Research. Source

Zhang X.,China University of Mining and Technology | Chen B.,China University of Mining and Technology | Chen B.,Jiangsu Center for Collaborative Innovation | Fan H.,China University of Mining and Technology | Zhu D.,China University of Mining and Technology
Canadian Journal of Remote Sensing

The main objective of this study is to develop a multifeature soil moisture retrieval method based on the principal component analysis (PCA) dimensionality reduction technique. RADARSAT-2 data were used to compute the backscattering coefficients and polarimetric variables. The optimal input features for soil moisture retrieval were selected by means of PCA dimensionality reduction and least root mean square error (RMSE) criterion. The support vector regression (SVR) model was used to estimate soil moisture content. The results indicated that the optimal features extracted by the PCA dimensionality reduction showed high correlation with soil moisture content. The RMSE, R2 (determination coefficient) and mean relative error (MRE) were (1.4 vol.%, 0.73, 18.2%) and (1.6 vol.%, 0.66, 15.6%) over the low grass cover areas A and B, respectively. For the bare soil areas A and B, the statistic results were (1.3 vol.%, 0.76, 12.1%) and (1.6 vol.%, 0.72, 14.9%), respectively. This case study confirmed the potential of the developed approach to estimate soil moisture over the low grass cover and bare soil areas. © CASI. Source

Zhang J.,Nanjing Normal University | Zhang J.,Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control | Zhang J.,Jiangsu Center for Collaborative Innovation | Muller C.,Justus Liebig University | And 4 more authors.
Soil Biology and Biochemistry

Nitrous oxide (N2O) is one of the key trace gases playing an important role in global climate change. Soils are the most important source of global N2O. A large number of studies have been conducted to quantify soil-based N2O emissions, including processes of N2O production, microbial mechanisms of N2O production, and the prediction of N2O emissions via various modeling approaches on various spatial scales. However, a considerable uncertainty still exists regarding the spatial and temporal variability of N2O emissions in natural and managed habitats. In this review, we summarize the nitrogen (N) pools related with N2O production and the methods quantifying the gross heterotrophic nitrification of organic N and its contribution to N2O emissions in soils, with the aim to derive a simplified conceptual approach for N2O emissions. We show that with current stable isotopes techniques such a quantification is possible and can propose more information to understand N2O emissions from a wide range of soil and ecosystems. The gross heterotrophic nitrification of organic N rate may be generally significant in acidic forest soils with high C/N ratio. However, the contribution of heterotrophic nitrification of organic N process to total N2O emissions seems to be dependent on soil pH, C/N ratio and land use. Therefore, we propose introducing N2O production via heterotrophic nitrification of organic N into the conceptual "hole-in-the-pipe" (HIP) model of N2O emission, originally developed by Firestone and Davidson (1989). © 2015 Elsevier Ltd. Source

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