A new coarse-time GPS positioning algorithm using combined Doppler and code-phase measurements   总被引：2，自引：2，他引：0  

Hung-Wei Chen  He-Sheng Wang  Yi-Te Chiang  Fan-Ren Chang 《GPS Solutions》2014,18(4):541-551

A new coarse-time Global Positioning System (GPS) positioning algorithm based on the use of Doppler and code-phase measurements is proposed and described. The proposed method was demonstrated to be essential for reducing the time to first fix and the power consumption in a GPS receiver. Only 1 ms of data is required to obtain a positioning fix with accuracy comparable to that of the traditional GPS navigation algorithm. The algorithm is divided into two parts. In the first part, the Doppler measurement of the GPS signal is used to determine the coarse user position. With proper constraints, the required time accuracy for the Doppler measurements can be relaxed to be as long as 12 h. In the second part of the algorithm, the accurate user position is calculated by means of the 1 ms code-phase data. The traditional tracking process is no longer necessary in the proposed algorithm. Using the acquired 1-ms code-phase measurement, the positioning accuracy was determined to be approximately a few tens of meters in our experimental results. However, if the data length is extended to 10 ms, the positioning accuracy can be improved to within 10–20 m, which is similar to that of the traditional GPS positioning method. Various experiments were conducted to verify the usefulness of the proposed algorithm.  相似文献   

广义点摄影测量在建筑物立面轮廓重构中的应用     

李畅  李熙  李彩林  李奇 《武汉大学学报(信息科学版)》2011,36(12):1451-1455

采用广义点摄影测量理论对建筑物立面框架轮廓进行重构。广义点是对当代线摄影测量以及无穷远点（灭点）理论的升华。实验结果表明,采用线面基元进行立面重构相比于经典的点云重构方法,不仅简洁、高效,还能获得清晰的三维边缘轮廓,且自动化程度较高。  相似文献   

2009-08-17山东特大暴雨雷达回波及地形作用分析   总被引：2，自引：0，他引：2  

高留喜  王彦  万明波  刘畅 《南京气象学院学报》2011,34(2):239-245

利用常规、非常规资料对2009年8月17—18日山东省出现的特大暴雨过程进行分析。结果表明：＂8.17＂特大暴雨主要出现在西风槽东移、副高南退时的副高西北侧边缘,对流有效位能（CAPE）等热力环境指数对鲁南强降水有较强的反应能力。降水分布具有典型的地形影响特征,复杂山地地形对降水有显著增幅作用和对对流系统传播的阻碍作用。存在低空急流和列车效应,强回波维持时间较长是费县出现强降水的重要原因,较强的偏南气流、湿度层深厚是费县出现特大暴雨的根本原因。地形影响气流理论很好地解释了山东＂8.17＂特大暴雨降水分布,费县特殊地形对特大暴雨有很大贡献。雷达资料可以弥补常规观测的不足;地形对强降雨及其分布有重要影响。  相似文献   

Frontal circulation induced by up-front and coastal downwelling winds     

Yu-Lin Chang  Lie-Yauw Oey 《Ocean Dynamics》2011,61(9):1345-1368

Two-dimensional (cross-shelf and depth) circulation by downwelling wind in the presence of a prograding front (with isopycnals that slope in the same direction as the topographic slope) over a continental shelf is studied using high-resolution numerical experiments. The physical process of interest is the cross-shelf circulation produced by northeasterly monsoon winds acting on the Kuroshio front over the East China Sea outer shelf and shelfbreak where upwelling is often observed. However, a general problem is posed and solved by idealized numerical and analytical models. It is shown that upwelling is produced shoreward of the front. The upwelling is maintained by (1) a surface bulge of negative vorticity at the head of the front; (2) bottom offshore convergence beneath the front; and (3) in the case of a surface front that is thin relative to water depth, also by upwelling due to the vorticity sheet under the front. The near-coast downwelling produces intense mixing due to both upright and slant-wise convection in regions of positive potential vorticity. The analytical model shows that the size and on-shore propagating speed of the bulge are determined by the wind and its shape is governed by a nonlinear advection–dispersion equation which yields unchanging wave-form solutions. Successive bulges can detach from the front under a steady wind. Vertical circulation cells develop under the propagating bulges despite a stable stratification. These cells can have important consequences to vertical exchanges of tracers and water masses.  相似文献   

Holocene East Asian monsoon variation inferred from species assemblage and shell chemistry of the ostracodes from Hulun Lake, Inner Mongolia   总被引：3，自引：0，他引：3  

Dayou Zhai  Jule Xiao  Lang Zhou  Ruilin Wen  Zhigang Chang  Xu Wang  Xindi Jin  Qiqing Pang  Shigeru Itoh 《Quaternary Research》2011,75(3):512-522

A sediment core from Hulun Lake, Inner Mongolia was analyzed for species assemblages and shell chemistry of ostracodes to investigate changes in the hydrology and climate of the East Asian summer monsoon margin during the Holocene. Darwinula stevensoni was abundant, Ilyocypris spp. scarce, littoral ostracodes absent and Mg/Ca, Sr/Ca and δ¹⁸O were low 11,100 to 8300 yr ago, indicating high lake levels and cool/fresh waters. Darwinula stevensoni declined largely, Ilyocypris spp. throve, littoral ostracodes were rare and chemical indicators remained in low values 8300 to 6200 yr ago, suggesting that the lake continued high stands but water became warm. The lake then contracted and water became cool/brackish 6200 to 4300 yr ago. Littoral ostracodes flourished 4300 to 3350 yr ago, marking the lowest lake levels of the entire Holocene. The lake level recovered and water salinity decreased 3350 to 1900 yr ago. From 1900 to 500 yr ago, the lake maintained the preceding status albeit lowered stands and increased salinities 1100 to 800 yr ago. During the recent 500 yr, the lake expanded and water salinity decreased. The data imply that the East Asian summer monsoon did not intensify until 8300 yr ago and weakened dramatically 4300 to 3350 yr ago.  相似文献   

Comparison of SPT-N-based analysis methods in evaluation of liquefaction potential during the 1999 Chi-chi earthquake in Taiwan     

Muhsiung Chang  Chih-ping Kuo  Shih-hui Shau  Ron-eeh Hsu 《Computers and Geotechnics》2011

SPT-N-based methods have been adopted for liquefaction assessment of soils during earthquakes for decades. However, there has not been a consistent way of assessing the accuracy and applicability of these methods. The Chi-chi earthquake of 1999, which has been the most serious ground shaking in Taiwan within the century, caused extensive liquefactions in mid-west alluvial deposits of the island. This paper assesses the prediction accuracy of several SPT-N-based methods using liquefaction and non-liquefaction incidents observed during the earthquake. A sensitivity study on commonly adopted parameters shows that the SPT blow count and peak ground acceleration are most sensitive in computing liquefaction potential. By comparing the error in predicting liquefaction and non-liquefaction incidents, this study concludes that Tokimatsu and Yoshimi’s method is more accurate than the other methods. However, the differences between prediction errors of various methods are minimal, indicating all of the methods examined are applicable for the 1999 earthquake in Taiwan.  相似文献   

Non-Circular Rock-Fall Motion Behavior Modeling by the Eccentric Circle Model     

Yi-Long Chang  Chien-Yuan Chen  An-Yuan Xiao 《Rock Mechanics and Rock Engineering》2011,44(4):469-482

The geometry of a block is a major factor affecting its rock-fall motion. A two-dimensional disc or three-dimensional sphere is often used to numerically simulate rock-fall motion, though circular or spherical blocks poorly represent the real geometry of rock falls. An eccentric circle model is specifically proposed to simulate the behavior of non-circular blocks in rock-fall motion using the distinct element method. In the eccentric circle model, the moment originates from the eccentricity. Three types of block shape, circle, ellipse, and eccentric circle, were used to simulate the fall of a single block through four different slope shapes to impact on a defense wall. The results of the simulation revealed that when the eccentricity falls below 0.5, the rock-fall motion is close to that of the ellipse model. As eccentricity grows, the rock-fall motion is closer to that of a flat piece, more stable, and tending to slide. When the block impacts the defensive wall using the circle model, a higher force and energy head in the wall is obtained. This case tends to be conservative, with the exception of the high slope angle case. The bouncing height using the circle model falls just between those of the ellipse and the eccentric circle models and tends to be unconservative. In conclusion, the rock-fall motion simulation using the proposed eccentric circle model appears to approach the non-circular block trajectory and energy loss, making it useful for rock-fall risk prevention and mitigation.  相似文献   

甘肃省舟曲县"8.8"特大山洪泥石流灾害与气象成因分析及其应对建议   总被引：1，自引：0，他引：1  

王志录  孙畅  包红霞  洪力强  高宇凤 《地质灾害与环境保护》2011,22(1):10-15

通过调查舟曲地质灾害历史资料.分析降雨与地质灾害的相关性,发现地质灾害与灾害前1～3 h累积降水量、月平均降水量和月暴雨频数明显正相关.然后分析舟曲"8.8"特大山洪泥石流的气象和降水成因.在此基础上,提出舟曲地质灾害的防治措施.  相似文献   

Geochemistry and origin of deep-seated cracked gas on the northern slope of the Dongying Sag, Shandong Province     

Xiangchun Chang  Zuozhen Han  Youde Xu  Xiaofei Shang  Chengpeng Yan 《中国地球化学学报》2011,30(3):353-358

Deep-seated cracked gas exploration was achieved great breakthrough in Es4L of the Minfeng area on the northern slope of the Dongying Sag. Carbon isotopic and molecular compositions studies revealed the characteristics of wet gas and a normal trend of carbon isotopic composition. Empirical cutoff points of δ13C2 and δ13C3 and light hydrocarbon compositions distinguished the cracking gas as sapropelic gas. Variations in i/nC5, i/nC4 and δ13C2 fur-ther confirmed that the gas was cracked from residual kerogen. Source characteristics indicated that the gas was de-rived from mature-highly mature source rocks of Es4 with kerogen type II being dominant mixed with some oil-cracking gas. Burial history modeling indicated that there were two hydrocarbon charging periods in Es4L reser-voirs. The first period refers to the Guantao-Minghuazhen stage dominated by oil charging, while the second period refers to the Minghuazhen stage and has been dominated by cracked gas charging till now.  相似文献   

黔南宾夕法尼亚亚纪礁环境中腕足动物古生态研究     

杨丽丽  巩恩普  关长庆  刘畅  张永利  常洪伦 《世界地质》2011,30(1):1-6

黔南地区宾夕法尼亚亚纪逍遥阶礁相地层中腕足动物普遍发育,主要产长身贝类和石燕贝类。本文主要研究该区腕足动物与造礁生物叶状藻和Fomitchevella 珊瑚之间的生态关系。在叶状藻礁内,小个体腕足动物常附着在藻叶上营假漂浮生活; 但藻叶密集处,小个体腕足动物也难见,可能藻丛造成水流循环不畅使腕足动物难以获得充足的食料; 藻叶稀疏处,腕足动物个体加大,数量增加。在大型Fomitchevella 珊瑚格架礁内,腕足动物与Fomitchevella 之间不存在食物上的竞争。腕足动物介壳层为Fomitchevella 幼虫定殖提供了生物成因的硬质基底,在此基础之上发育了大型珊瑚礁。腕足动物在 Fomitchevella 进入统殖阶段由于生态空间受到局限而退居次要地位。  相似文献