摘要：
A combination of GPS and GLONASS observations can offer improved reliability, availability and accuracy for precise point positioning (PPP). We present and analyze a combined GPS/GLONASS PPP model, including both functional and stochastic components. Numerical comparison and analysis are conducted with respect to PPP based on only GPS or GLONASS observations to demonstrate the benefits of the combined GPS/GLONASS PPP. The observation residuals are analyzed for more appropriate stochastic modeling for observations from different navigation systems. An analysis is also made using different precise orbit and clock products. The performance of the combined GPS/GLONASS PPP is assessed using both static and kinematic data. The results indicate that the convergence time can be significantly reduced with the addition of GLONASS data. The positioning accuracy, however, is not significantly improved by adding GLONASS data if there is a sufficient number of GPS satellites with good geometry.
作者：
Zou, Bin*;Wilson, J. Gaines;Zhan, F. Benjamin;Zeng, Yongnian
期刊：
Journal of environmental monitoring : JEM,2009年11(3):475-490 ISSN：1464-0325
通讯作者：
Zou, Bin
作者机构：
[Zou, Bin; Zeng, Yongnian] Cent S Univ, Sch Infophys & Geomat Engn, Changsha 410086, Hunan, Peoples R China.;[Zhan, F. Benjamin; Zou, Bin] Texas State Univ, Texas Ctr Geog Informat Sci, Dept Geog, San Marcos, TX 78666 USA.;[Wilson, J. Gaines] Univ Texas Brownsville, Dept Chem & Environm Sci, Brownsville, TX 78520 USA.;[Zhan, F. Benjamin] Wuhan Univ, Sch Resource & Environm Sci, Wuhan 430079, Hubei, Peoples R China.
通讯机构：
[Zou, Bin] Cent S Univ, Sch Infophys & Geomat Engn, Changsha 410086, Hunan, Peoples R China.
摘要：
The assessment of personal exposure to air pollution is a critical component of epidemiological studies associating air pollution and health effects. This paper critically reviewed 157 studies over 29 years that utilized one of five categories of exposure methods (proximity, air dispersion, hybrid, human inhalation, and biomarkers). Proximity models were found to be a questionable technique as they assume that closer proximity equates to greater exposure. Inhalation models and biomarker estimates were the most effective in assessing personal exposure, but are often cost prohibitive for large study populations. This review suggests that: (i) factors such as uncertainty, validity, data availability, and transferability related to exposure assessment methods should be considered when selecting a model; and (ii) although an entirely discreet new class of approach is not necessary, significant progress could be made through the development of a 'hybrid' model utilizing the strengths of several existing methods. Future work should systematically evaluate the performance of hybrid models compared to other individual exposure assessment methods utilizing geospatial information technologies (e.g. geographic information systems (GIS) and remote sensing (RS)) to more robustly refine estimates of ambient exposure and quantify the linkages and differences between outdoor, indoor and personal exposure estimates.
摘要：
In this letter, different from traditional methods using original spectral features or handcraft spectral-spatial features, we propose to adaptively learn a suitable feature representation from unlabeled data. This is achieved by learning a feature mapping function based on stacked sparse autoencoder. Considering that hyperspectral imagery (HSI) is intrinsically defined in both the spectral and spatial domains, we further establish two variants of feature learning procedures for sparse spectral feature learning and multiscale spatial feature learning. Finally, we embed the learned spectral-spatial feature into a linear support vector machine for classification. Experiments on two hyperspectral images indicate the following: 1) the learned spectral-spatial feature representation is more discriminative for HSI classification compared to previously hand-engineered spectral-spatial features, especially when the training data are limited and 2) the learned features appear not to be specific to a particular image but general in that they are applicable to multiple related images (e.g., images acquired by the same sensor but varying with location or time).
摘要：
Infrared small-target detection plays an important role in image processing for infrared remote sensing. In this letter, different from traditional algorithms, we formulate this problem as salient region detection, which is inspired by the fact that a small target can often attract attention of human eyes in infrared images. This visual effect arises from the discrepancy that a small target resembles isotropic Gaussian-like shape due to the optics point spread function of the thermal imaging system at a long distance, whereas background clutters are generally local orientational. Based on this observation, a new robust directional saliency-based method is proposed incorporating with visual attention theory for infrared small-target detection. Experimental results demonstrate that the proposed algorithm outperforms the state-of-the-art methods for real infrared images with various typical complex backgrounds.
作者机构：
[Zhao, Yu; Hu, Mao-Gui; Wang, Jin-Feng; Xu, Cheng-Dong] Chinese Acad Sci, Inst Geog Sci & Nat Resources Res, State Key Lab Resources & Environm Informat Syst, Beijing, Peoples R China.;[Christakos, George] San Diego State Univ, Dept Geog, San Diego, CA 92182 USA.;[Zhao, Yu] Cent S Univ, Sch Geosci & Infophys, Changsha, Hunan, Peoples R China.
通讯机构：
[Wang, Jin-Feng] Chinese Acad Sci, Inst Geog Sci & Nat Resources Res, State Key Lab Resources & Environm Informat Syst, Beijing, Peoples R China.
关键词：
Air pollution,Pollution,Air quality,Pollutants,Covariance,Environmental protection,Municipal governments,Urban areas
摘要：
There has been discrepancies between the daily air quality reports of the Beijing municipal government, observations recorded at the U.S. Embassy in Beijing, and Beijing residents' perceptions of air quality. This study estimates Beijing's daily area PM(2.5) mass concentration by means of a novel technique SPA (Single Point Areal Estimation) that uses data from the single PM(2.5) observation station of the U.S Embassy and the 18 PM(10) observation stations of the Beijing Municipal Environmental Protection Bureau. The proposed technique accounts for empirical relationships between different types of observations, and generates best linear unbiased pollution estimates (in a statistical sense). The technique extends the daily PM(2.5) mass concentrations obtained at a single station (U.S. Embassy) to a citywide scale using physical relations between pollutant concentrations at the embassy PM(2.5) monitoring station and at the 18 official PM(10) stations that are evenly distributed across the city. Insight about the technique's spatial estimation accuracy (uncertainty) is gained by means of theoretical considerations and numerical validations involving real data. The technique was used to study citywide PM(2.5) pollution during the 423-day period of interest (May 10, 2010 to December 6, 2011). Finally, a freely downloadable software library is provided that performs all relevant calculations of pollution estimation.
摘要：
The usefulness of gravity-based spatial access models is limited because of the uncertainty introduced by the range of values of the impedance coefficient. To solve this problem, this paper proposes the concept of spatial access ratio (SPAR) derived from the enhanced 2-step floating catchment area (E2SFCA) method — a recent extension of the gravity model — to assess potential spatial access. First, a sensitivity assessment is conducted to verify the effectiveness of SPAR and its advantages in overcoming the uncertainty problem. Then, the E2SFCA method and the shortest travel time method are employed to measure potential spatial access to colorectal cancer (CRC) prevention and treatment services in Texas based on data at the census tract level. The socio-demographic and geographic distributions of potential spatial access to CRC services are also examined. The sensitivity assessment reveals substantial fluctuations in the values of the spatial access index calculated directly by the E2SFCA method under different values of the impedance coefficient. However, the values of SPAR remain stable under different values of the coefficient. A comparative analysis indicates that potential spatial access to primary care physicians (PCPs), CRC screening facilities, and oncologists varied among different racial/ethnic and socioeconomic population groups as well as in different geographic regions in Texas. Non-Hispanic blacks, Asians, and people in affluent areas had a geographical advantage in accessing CRC services than other groups. The urban/rural difference was more obvious and serious than those of different racial/ethnic groups and groups with different socio-economic statuses, as metropolitan residents had more than three times the potential spatial access than isolated rural residents.
作者机构：
[Li, Z. W.; Sun, Q.; Hu, J.; Zhu, J. J.] Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.;[Ding, X. L.; Zhang, L.] Hong Kong Polytech Univ, Dept Land Surveying & Geoinformat, Kowloon, Hong Kong, Peoples R China.
通讯机构：
[Li, Z. W.] Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
摘要：
One-dimensional measurement along the Line-Of-Sight (LOS) direction has greatly limited the capability of InSAR technique in the investigation of surface displacements and their dynamics. In recent years, great efforts have been made to resolve complete three-dimensional (3-D) displacements from InSAR measurements. This contribution is intended to provide a systematic review of the progress achieved in this field. Based on an analysis of the InSAR LOS measurements, we first cover two commonly used techniques, i.e., Offset-Tracking and multi-aperture InSAR (MAI), with which the surface displacement in the azimuth direction can be measured together with the LOS displacement. Several methods for mapping 3-D displacements using InSAR measurements are subsequently presented and categorized into three groups: (i) combination of multi-pass LOS and azimuth measurements; (ii) integration of InSAR and GPS data; and (iii) prior information assisted approaches. The strengths and weaknesses of each method are analyzed to show the applicability of each method to specific 3-D displacement mapping cases, in hope to provide a useful guidance in choosing a suitable approach accordingly. Finally, suggestions for resolving the challenging issues and outlook of future research are given. (c) 2014 Elsevier B.V. All rights reserved.
摘要：
To meet the challenges of designing an in situ forming scaffold and regenerating bone with complex three-dimensional (3D) structures, an in situ forming hydrogel scaffold based on nano-hydroxyapatite (nHA), collagen (Col), and chitosan (CS) was synthesized. Currently, only a limited number of techniques are available to mediate and visualize the injection process of the injectable biomaterials directly and noninvasively. In this study, the potential of ultrasound for the quantitative in vivo evaluation of tissue development in CS/nHAC scaffold was evaluated. The CS/nHAC scaffold was injected into rat subcutaneous tissue and evaluated for 28 days. Quantitative measurements of the gray-scale value, volume, and blood flow of the scaffold were evaluated using diagnostic technique. This study demonstrates that ultrasound can be used to noninvasively and nondestructively monitor and evaluate the in vivo characteristics of injectable bone scaffold. In comparison to the CS, the CS/nHAC scaffold showed a greater stiffness, less degradation rate, and better blood supply in the in vivo evaluation. In conclusion, the diagnostic ultrasound method is a good tool to evaluate the in vivo formation of injectable bone scaffolds and facilitates the broad use to monitor tissue development and remodeling in bone tissue engineering.
摘要：
We analyze a large amount of receiver function data recorded by regional seismic networks of the China Earthquake Administration to estimate crustal structure and deformation beneath the southeast margin of the Tibetan plateau and its surrounding areas. We develop a comprehensive analysis method that facilitates robust extraction of azimuthal seismic anisotropy from receiver function data. The method includes an estimate of fast polarization direction and splitting time by a joint analysis of radial and transverse receiver function data, and an evaluation of measurement reliability by statistical and harmonic analysis. We find significant seismic anisotropy with a splitting time of 0.5-0.9 s beneath the SE margin of the Tibetan plateau. Both the splitting time and fast polarization direction are comparable to those estimated from SKS/SKKS data, suggesting that crustal anisotropy is the main cause of shear wave splitting of the SKS/SKKS wave. This also suggests that deformation in the upper mantle is either weak or predominantly vertical, and is obviously different from the one in the crust. A vertical flow in the upper mantle, combined with the observation of a thin lithosphere beneath the study area, leads to the inference that part of the mantle lithosphere may have been removed and is descending into deep mantle. Stations located in the surrounding areas, on the other hand, exhibit very little to no crustal anisotropy. The estimated Moho depth and Vp/Vs ratio also show a distinct difference between the SE Tibetan plateau and the surrounding regions. Stations on the Tibetan plateau have a Vp/Vs ratio of similar to 1.79, which is substantially higher than those measured at the Yunnan-Guizhou (Yungui) plateau (similar to 1.69). Our observations here are consistent with the scenario that the SE Tibet has been built by lower crustal flow. They also suggest that the mantle lithosphere beneath the margin may have been mechanically decoupled from the upper crust. (C) 2012 Elsevier B.V. All rights reserved.
作者：
Feng, GuangCai*;Hetland, Eric A.;Ding, XiaoLi;Li, ZhiWei;Zhang, Lei
期刊：
Geophysical Research Letters,2010年37(1):- ISSN：1944-8007
通讯作者：
Feng, GuangCai
作者机构：
[Ding, XiaoLi; Feng, GuangCai; Zhang, Lei] Hong Kong Polytech Univ, Dept Land Surveying & Geoinformat, Kowloon, Hong Kong, Peoples R China.;[Hetland, Eric A.] Univ Michigan, Dept Geol Sci, Ann Arbor, MI 48109 USA.;[Li, ZhiWei] Cent S Univ, Dept Geomat, Changsha 410083, Peoples R China.
通讯机构：
[Feng, GuangCai] Hong Kong Polytech Univ, Dept Land Surveying & Geoinformat, Kowloon, Hong Kong, Peoples R China.
关键词：
coseismic slip;InSAR;earthquake
摘要：
[1] We infer co‐seismic fault slip during the 2008 Mw 7.9 Wenchuan earthquake from interferometric synthetic aperture radar (InSAR) and GPS observations of ground deformation. We use ALOS/PALSAR data from ascending orbits on six tracks, and we do not use data that are strongly affected by ionospheric perturbations. We use a fault model composed of three planar fault segments of the Beichuan fault, and one planar segment representing the parallel Pengguan fault. Maximum thrust‐slip is up to 6.7 m near the surface, and occurs in two locations, near Yingxiu in the south and Beichuan in the center of the rupture. Maximum strike‐slip is over 4 m, and occurs near Pingtong and Nanba along the northern end of the rupture. We find that the ratio of coseismic thrust‐ to strike‐slip on the Beichuan fault decreases from 1.5 to 0.7 from the SW to the NE.
期刊：
International Journal for Numerical and Analytical Methods in Geomechanics,2010年34(17):1767-1796 ISSN：0363-9061
通讯作者：
Zhao, Chongbin
作者机构：
[Zhao, Chongbin] Cent S Univ, Computat Geosci Res Ctr, Changsha 410083, Peoples R China.;[Hobbs, B. E.; Ord, A.] Univ Western Australia, Sch Earth & Environm, Crawley, WA 6009, Australia.;[Hobbs, B. E.; Ord, A.] CSIRO, Div Explorat & Min, Bentley, WA 6102, Australia.
通讯机构：
[Zhao, Chongbin] Cent S Univ, Computat Geosci Res Ctr, Changsha 410083, Peoples R China.
关键词：
nonaqueous phase liquid;residual saturation;NAPL dissolution;front instability;reactive mass transport;porous media
摘要：
This paper deals with the theoretical aspects of nonaqueous phase liquid (NAPL)-dissolution-induced instability in two-dimensional fluid-saturated porous media including solute dispersion effects. After some weaknesses associated with the previous work are analyzed and overcome, a comprehensive dimensionless number, known as the Zhao number, is proposed to represent the main driving force and three controlling mechanisms of an NAPL-dissolution system that has a finite domain. The linear stability analysis is carried out to derive the critical value of the comprehensive dimensionless number of the NAPL-dissolution system in a limit case as the ratio of the equilibrium concentration to the density of the NAPL approaches zero. As a result, a theoretical criterion that can be used to assess the instability of planar NAPL-dissolution fronts in two-dimensional fluid-saturated porous media of finite domains has been established. Not only can the present theoretical results be used for the theoretical understanding of the effect of solute dispersion on the instability of an NAPL-dissolution front in the fluid-saturated porous medium of either a finite domain or an infinite domain, but also they can be used as benchmark solutions for verifying numerical methods employed to simulate detailed morphological evolution processes of NAPL-dissolution fronts in two-dimensional fluid-saturated porous media. Copyright (C) 2009 John Wiley & Sons, Ltd.
摘要：
Satellite-retrieved aerosol optical depth (AOD) has been increasingly utilized for the mapping of fine particulate matter (PM
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) concentrations. An accurate estimation and mapping of PM
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concentrations depends on the high-resolution AOD data and a robust mathematical model that takes into account the spatial nonstationary relationship between PM
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and AOD. Take the core portion of the Beijing-Hebei-Tianjin (Jing-Jin-Ji) urban agglomeration as case study (the most seriously polluted region in China). Land use, population, meteorological variables, and simplified aerosol retrieval algorithm-retrieved AOD at 1-km resolution are employed as the predictors for the geographically weighted regression (GWR) and the ordinary least squares (OLS) model to map the spatial distribution of PM
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concentrations. The GWR model shows significant spatial variations in PM
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concentrations over the region than the traditional OLS model, which reveals relative homogeneous variations. Validation with ground-level PM
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concentrations demonstrates that PM
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concentrations predicted by the GWR model (R
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= 0.75, RMSE = 10 μg/m
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) correlate better than those by the OLS model (R
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= 0.53, RMSE = 16 μg/m
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). These results suggest that the GWR model offered a more reliable way for the prediction of spatial distribution of PM
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concentrations over urban areas.
