层间氧化带砂岩型铀矿地电化学异常形成机理及其找矿意义     

柯丹  刘洪军  侯惠群  吴国东  郝伟林  易超 《地质学报》2016,90(12):3545-3553

层间氧化带砂岩型铀矿是我国主要的砂岩型铀矿类型之一,属全盲矿,找矿难度大。地电化学方法作为深穿透地球化学方法的分支之一,为隐伏铀矿勘查提供了新的技术手段,并在实际找矿中取得了明显的效果。研究表明,在隐伏砂岩型铀矿上方,存在着地电化学提取U元素异常。总结和分析了层间氧化带砂岩型铀矿形成的物理化学条件以及在实际试验中发现的铀矿上方地电提取铀异常特征,在前人提出的元素由深部向地表迁移机制的基础上,进一步归纳了砂岩型铀矿地电化学异常的形成机理。层间氧化带砂岩型铀矿上方地电提取U元素主要呈现为跳跃的锯齿状高值异常,可以作为深部铀矿找矿的指示标志。  相似文献   

国家环境遥感监测体系研究与实现   总被引：3，自引：0，他引：3  

王桥  刘思含 《遥感学报》2016,20(5):1161-1169

随着国家空间基础设施的建设和发展,中国遥感监测体系研究与建设取得了重大突破,从无到有形成了国家环境遥感监测能力,并业务化实现了主要环境遥感监测要素产品的生产与服务,为新时期环境管理工作提供了有力支撑。在分析国内外环境遥感发展及中国环境遥感监测需求的基础上,阐述了中国环境监测体系建设的必要性,研究了国家环境遥感监测体系的建立与业务化运行,提出了中国环境遥感监测体系发展思路与下一步重点任务。  相似文献   

A closed-loop EKF and multi-failure diagnosis approach for cooperative GNSS positioning     

Haiying Liu  Xiaolin Meng  Zhiming Chen  Scott Stephenson  Pekka Peltola 《GPS Solutions》2016,20(4):795-805

Current cooperative positioning with global navigation satellite system (GNSS) for connected vehicle application mainly uses pseudorange measurements. However, the positioning accuracy offered cannot meet the requirements for lane-level positioning, collision avoidance and future automatic driving, which needs real-time positioning accuracy of better than 0.5 m. Furthermore, there is an apparent lack of research into the integrity issue for these new applications under emerging driverless vehicle applications. In order to overcome those problems, a new extended Kalman filter (EKF) and a multi-failure diagnosis algorithm are developed to process both GNSS pseudorange and carrier phase measurements. We first introduce a new closed-loop EKF with partial ambiguity resolution as feedback to address the low accuracy issue. Then a multi-failure diagnosis algorithm is proposed to improve integrity and reliability. The core of this new algorithm includes using Carrier phase-based Receiver Autonomous Integrity Monitoring method for failure detection, and the double extended w test detectors to identify failure. A cooperative positioning experiment was carried out to validate the proposed method. The results show that the proposed closed-loop EKF can provide highly accurate positioning, and the multi-failure diagnosis method is effective in detecting and identifying failures for both code and carrier phase measurements.  相似文献   

Weak GPS signal tracking using FFT discriminator in open loop receiver     

Kunlun Yan  Nesreen I. Ziedan  Hongping Zhang  Wenfei Guo  Xiaoji Niu  Jingnan Liu 《GPS Solutions》2016,20(2):225-237

An open loop tracking architecture, which tracks GPS signals under weak and challenging conditions, is analyzed. The in-phase and quadrature-phase integration pair is regarded as a single tone complex signal. An FFT-based method is used as a frequency discriminator to estimate the Doppler frequency residual of the single tone signal. Another FFT-based method applies complex squaring to eliminate the effect of the navigation data bits polarities. The performance of the FFT-based discriminators is assessed in three criteria. Those criteria are the signal strength and dynamic range that can be tracked and the accuracy of the estimated Doppler frequency. In addition, the performance of the discriminators is analyzed to provide the theoretical and simulated peak detection probability. The results indicate that the FFT discriminator can track signals about 5 dB weaker than the signals that can be tracked by the complex squared FFT discriminator. In a quasi-static environment, the Doppler frequency residual can be assumed to be around zero, which can enable the FFT-based discriminators to track signals with approximately 2 dB less power. Moreover, the performance of the FFT-based discriminators is compared with the performance of two other frequency discriminators, namely the fast–slow and power-based. The comparison results indicate that these two frequency discriminators give higher frequency estimation accuracy, but they have a narrower dynamic range.  相似文献   

Precise orbit determination of BeiDou constellation: method comparison   总被引：3，自引：1，他引：2  

Yidong Lou  Yang Liu  Chuang Shi  Bin Wang  Xiuguang Yao  Fu Zheng 《GPS Solutions》2016,20(2):259-268

Chinese BeiDou navigation satellite system is in official service as a regional constellation with five geostationary earth orbit (GEO) satellites, five inclined geosynchronous satellite orbit (IGSO) satellites and four medium earth orbit (MEO) satellites. There are mainly two methods for precise orbit determination of the BeiDou constellation found in the current literatures. One is the independent single-system method, where only BeiDou observations are used without help from other GNSS systems. The other is the two-step GPS-assisted method where in the first step, GPS data are used to resolve some common parameters, such as station coordinates, receiver clocks and zenith tropospheric delay parameters, which are then introduced as known quantities in BeiDou processing in the second step. We conduct a thorough performance comparison between the two methods. Observations from the BeiDou experimental tracking stations and the IGS Multi-GNSS Experiment network from January 1 to March 31, 2013, are processed with the Positioning and Navigation Data Analyst (PANDA) software. The results show that for BeiDou IGSO and MEO satellites, the two-step GPS-assisted method outperforms the independent single-system method in both internal orbit overlap precision and external satellite laser ranging validation. For BeiDou GEO satellites, the two methods show close performances. Zenith tropospheric delays estimated from the first method are very close to those estimated from GPS precise point positioning in the second method, with differences of several millimeters. Satellite clock estimates from the two methods show similar performances when assessing the stability of the BeiDou on board clocks.  相似文献   

An Immune Genetic Algorithm to Buildings Displacement in Cartographic Generalization          下载免费PDF全文

Yageng Sun  Qingsheng Guo  Yuangang Liu  Xiaoya Ma  Jie Weng 《Transactions in GIS》2016,20(4):585-612

Spatial conflicts may occur when map data are displayed at a scale smaller than that of the source map. This study applies the displacement operator in cartographic generalization to resolve such spatial conflicts and to improve the clarity and legibility of map. The immune genetic algorithm (IGA) is used in this study for buildings displacement to solve conflicts. IGA is based on the genetic algorithm (GA) and employs the self‐adjusting mechanism of antibody concentration to enhance population diversity. Meanwhile, the elitism retention strategy is adopted in IGA to guarantee that the best individual (antibody) is not lost and destroyed in the next generation to strengthen convergence efficiency. The compared experiment between IGA and GA shows that the displacement result produced by IGA performs better than GA. Finally, in order to make the displaced map more attractive to cartographers, two constraints – the building alignment constraint and building tangent relation constraint – are applied in IGA to restrict the buildings’ displacement. The same experimental data are adopted to prove that the improved IGA is useful for maintaining the two constraints.  相似文献   

Geographical impacts on social networks from perspectives of space and place: an empirical study using mobile phone data   总被引：2，自引：0，他引：2  

Li Shi  Lun Wu  Guanghua Chi  Yu Liu 《Journal of Geographical Systems》2016,18(4):359-376

Space and place are two fundamental concepts in geography. Geographical factors have long been known as drivers of many aspects of people’s social networks. But whether and how space and place affect social networks differently are still unclear. The widespread use of location-aware devices provides a novel source for distinguishing the mechanisms of their impacts on social networks. Using mobile phone data, this paper explores the effects of space and place on social networks. From the perspective of space, we confirm the distance decay effect in social networks, based on a comparison between synthetic social ties generated by a null model and actual social ties derived from real-world data. From the perspective of place, we introduce several measures to evaluate interactions between individuals and inspect the trio relationship including distance, spatio-temporal co-occurrence, and social ties. We found that people’s interaction is a more important factor than spatial proximity, indicating that the spatial factor has a stronger impact on social networks in place compared to that in space. Furthermore, we verify the hypothesis that interactions play an important role in strengthening friendships.  相似文献   

Fourier-based multi-scale representation and progressive transmission of cartographic curves on the internet   总被引：1，自引：0，他引：1  

Pengcheng Liu  Weibo Liu  Tinghua Ai 《制图学和地理信息科学》2016,43(5):454-468

ABSTRACT

Automatic generation of multi-scale representations from the same spatial data source has been the research focus in map generalization for a long time. Based on the Fourier technique, this paper proposes a continuous, multi-scale representation model for progressive transformation of cartographic curves on the Internet. In our method, all the curves, whether closed or open, are depicted as periodical functions which are further expressed as Fourier series. The convergence degrees of the Fourier series are explored for different kinds of curves, and truncating frequencies are derived based on the similarity between the original and reconstructed curves. Using information theory and the Radical Law in cartography, the relationship between map scales and Fourier frequencies is established. Based on the proposed multi-scale model, we also introduce the principles and implementation of a progressive transmission method. Our method is evaluated using the contours from a topographic map. The results show that our model is a valid approach to multi-scale representation of cartographic curves.  相似文献   

A Method for Dynamic Risk Assessment and Management of Rockbursts in Drill and Blast Tunnels     

Guo-Feng Liu  Xia-Ting Feng  Guang-Liang Feng  Bing-Rui Chen  Dong-Fang Chen  Shu-Qian Duan 《Rock Mechanics and Rock Engineering》2016,49(8):3257-3279

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Assessment of storm surge inundation and potential hazard maps for the southern coast of Taiwan     

Wei-Bo Chen  Wen-Cheng Liu 《Natural Hazards》2016,82(1):591-616

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