Indoor Positioning Based on Pedestrian Dead Reckoning and Magnetic Field Matching for Smartphones.

This paper presents an ambient magnetic field map-based matching (MM) positioning algorithm for smartphones in an indoor environment. To improve the low distinguishability of a magnetic field fingerprint at a single point, a magnetic field sequence (MFS) combined with the measured trajectory contour coming from pedestrian dead-reckoning (PDR) is used for MM. Based on the fast approximation of magnetic field gradient, a Gauss-Newton iterative (GNI) method is used to find a rigid transformation that optimally aligns the measured MFS with a reference MFS coming from the magnetic field map. Then, the position of the reference MFS is used to control the position drift error of the inertial navigation system (INS) based PDR by an extended Kalman filter (EKF) and to further improve the accuracy of the trajectory contour. Finally, we conduct several experiments to evaluate the navigation performance of the proposed MM algorithm. The test results show that the position estimation error of the MM algorithm is 0.64 m (RMS) in an office building environment, 1.87 m (RMS) in a typical lobby environment, and 2.34 m (RMS) in a shopping mall environment.

Robust Pedestrian Dead Reckoning Based on MEMS-IMU for Smartphones.

This paper proposes a pedestrian dead reckoning (PDR) algorithm based on the strap-down inertial navigation system (SINS) using the gyros, accelerometers, and magnetometers on smartphones. In addition to using a gravity vector, magnetic field vector, and quasi-static attitude, this algorithm employs a gait model and motion constraint to provide pseudo-measurements (i.e., three-dimensional velocity and two-dimensional position increment) instead of using only pseudo-velocity measurement for a more robust PDR algorithm. Several walking tests show that the advanced algorithm can maintain good position estimation compare to the existing SINS-based PDR method in the four basic smartphone positions, i.e., handheld, calling near the ear, swaying in the hand, and in a pants pocket. In addition, we analyze the navigation performance difference between the advanced algorithm and the existing gait-model-based PDR algorithm from three aspects, i.e., heading estimation, position estimation, and step detection failure, in the four basic phone positions. Test results show that the proposed algorithm achieves better position estimation when a pedestrian holds a smartphone in a swaying hand and step detection is unsuccessful.

Arsenic content and fractionation in the surface sediments of the Guangzhou section of the Pearl River in Southern China.

The Guangzhou section of the Pearl River (GSPR) has been seriously affected by long-term intensive industrial and urban activities. The objectives of this study were to determine the total As (TAs) content and the forms of that As in order to investigate the geochemical relationships between As forms and sediment mineral phases of the surface sediments of the GSPR. Fifteen samples of surface sediment were collected and analyzed for TAs as well as As chemical forms. Results indicated that TAs in the sediment samples averaged 24.6 mg kg(-1) and ranged from 16.7 to 33.4 mg kg(-1). These values are generally higher than the probable effect level of 17.0 mg kg(-1). The As was mostly associated with iron oxides (53.5%), followed by association with the residual fraction (36.2%). Amor-Fe bound As and Cry-Fe bound As quantities were positively correlated to the Amor-Fe and Cry-Fe quantities, respectively. In addition, organic matter (OM), clay and Sum-Fe contents were positively correlated to TAs in the sediment fractions. The molar ratios of iron oxide-bound As to iron content approached the maximum molar ratios of As to Fe for natural hematite, magnetite, and goethite. Adverse effects caused by As will likely frequently occur at these high levels of As contamination. Thus, it is necessary to remediate the sediment of the GSPR to reduce the potential risks of As contamination.

Potential toxic risk of heavy metals from sediment of the Pearl River in South China.

Based on the monitoring of five heavy metal elements in the surface sediments of the Pearl River in South China, potential toxicity of the heavy metals was assessed using consensus-based sediment quality guidelines (SQGs) method and geo-accumulation (I(geo)) index method. The monitoring results showed the heavy metal concentrations were significantly and positively correlated with each other, demonstrating a common trend in variation of concentration in the surface sediments. The assessment using the consensus-based SQGs method showed the potential toxicity of Cu was the highest, and Cd was the lowest. The evaluation based on mean probable effect concentration (PEC) quotient showed the region was seriously polluted with high toxicity heavy metals. Correlation analysis revealed a significant and positive correlation between the mean PEC quotient and the average of I(geo) with a correlation coefficient of 0.926 (n = 23, P < 0.01). In conclusion, the consensus-based SQGs and mean PEC quotient are applicable to assess potential toxicity risks of heavy metals in freshwater sediments in the Pearl River.

Characteristics of indoor/outdoor PM2.5 and elemental components in generic urban, roadside and industrial plant areas of Guangzhou City, China.

Quantitative information on mass concentrations and other characteristics, such as spatial distribution, seasonal variation, indoor/outdoor (I/O) ratio, correlations and sources, of indoor and outdoor PM2.5 and elemental components in Guangzhou City were provided. Mass concentration of PM2.5 and elemental components were determined by standard weight method and proton-induced X-ray emission (PIXE) method. 18 elements were detected, the results showed positive results. Average indoor and outdoor PM2.5 concentrations in nine sites were in the range of 67.7-74.5 microg/m3 for summer period, and 109.9-123.7 microg/m3 for winter period, respectively. The sum of 18 elements average concentrations were 5362.6-5533.4 ng/m3 for summer period, and 8416.8-8900.6 ng/m3 for winter period, respectively. Average concentrations of PM2.5 and element components showed obvious spatial characteristic, that the concentrations in roadside area and in industrial plant area were higher than those in generic urban area. An obvious seasonal variation characteristic was found for PM2.5 and elemental components, that the concentrations in winter were higher than that in summer. The I/O ratio of PM2.5 and some elemental components presented larger than 1 sometimes. According to indoor/outdoor correlation of PM2.5 and element concentrations, it was found that there were often good relationships between indoor and outdoor concentrations. Enrichment factors were calculated to evaluate anthropogenic versus natural elements sources.

[Comprehensive assessment of urban ecosystem health].

Ecosystem health is one of the research hotspots in ecology. This paper discussed the concept of urban ecosystem health, and from the viewpoint of complex ecosystem, presented a new method and a calculation model for the comprehensive assessment of urban ecosystem health to overcome the current researches shortcomings. The application of the method and model in Foshan City of Guangdong Province showed that the assessment results could reflect not only the overall health status of the city, but also the relative health level of the city's sub-systems.

[Application of entropy weight and fuzzy synthetic evaluation in urban ecological security assessment].

Ecological security is one of the foundations of regional security, and the basis of sustainable development. Urban ecological security refers to the ecological support and main ecological issues of a city, which do not threaten its survival and development. To develop the research method on the ecological security of urban social-economic-natural complex ecosystem, an assessment indicator system of urban ecological security was set up based on Pressure - State - Response Model, which included 3 key factors and 33 concrete items. The five most developed cities of China were taken as the cases to assess their ecological security situation by using entropy weight and fuzzy synthetic evaluation method. The results showed that the urban ecological security of Suzhou and Beijing was at relatively safe level, while that of Shenzhen, Shanghai and Guangzhou was critical safe in the year of 2003. The urban ecosystem of Shenzhen was under heavy press, while that of Suzhou behaved best both in system status and system response. Comparing with other assessment methods, this evaluation method was easier and more reasonable. The results were basically consistent to the fact of these cities, suggesting that the urban ecological security indicator system and the entropy weight and fuzzy synthetic evaluation approach were feasible to some extent.