锚固站对BDS自主导航精度的影响分析     

龚晓颖  蔡诗响 《测绘通报》2020,(4):68-75

介绍了自主导航的轨道确定及时间同步观测方程。以北斗仿真全星座为对象，通过采用仿真星间及卫星与地面锚固站间观测值，进行了60 d自主导航解算，分别探讨了锚固站数量及锚固站观测连续性对北斗卫星导航系统（BDS）3类卫星自主导航精度的影响。结果表明：锚固站数量及观测连续性对RERR及CERR无影响；加入1个锚固站即可显著改进URE结果精度，继续增加锚固站数量虽然可进一步提高URE精度但其改进效果有限；锚固站观测中断时间越长，其对应自主导航精度越低。因此，在BDS自主导航运行模式下应保持较高的锚固站观测频次以保证自主导航精度；另外，锚固站数量及观测连续性对北斗系统3类卫星自主导航精度的影响无显著差异。  相似文献   

基于沉积过程的数字岩石建模方法研究          下载免费PDF全文

田志  肖立志  廖广志  董虎  田守嶒  宋先知 《地球物理学报》2019,62(1):248-259

本文提出模拟地层沉积及成岩过程的矿物沉积算法,建立数字岩石模型,并通过对比Micro-CT扫描图像和数值模型的局部孔隙度及平均渗流概率函数分布特征,评价建模的准确性.结果表明,由二维扫描提取的粒径信息作为输入参数,模拟矿物沉积过程建模得到的三维数字岩石模型,能够准确重构原始岩心的非均质性及渗流特性,成功应用于泥质砂岩、碳酸盐岩、页岩等存在多矿物或多尺度孔隙的数字岩石建模中.数字岩石物理是正在兴起的重要技术.数字岩石采用超高分辨率先进成像装备,采集和表征微纳尺度岩石结构,在岩石弹性、电性、核磁、渗流特性等数值计算中发挥重要作用.但是,由于三维直接成像在有限视域内难以表征足够的岩石非均质性,提取二维结构统计特征,利用统计或地质过程法重构具有代表性的三维岩石结构成为十分有价值的研究课题,而且,对业界大量存在的岩石薄片及电镜高清二维图像的深度开发应用也具有重要的现实意义.本文发展的新方法,复原沉积过程,较好地解决了孔隙尺度岩石物理定量研究中数值建模与理论计算的技术瓶颈.  相似文献   

Evaluation of aquatic ecological systems through dynamics of ichthyofaunal diversity in a Himalayan torrential river,Murti     

《Limnologica》2020

The biodiversity hotspot region of the Eastern Himalayas consists of a vast freshwater network enriched with species diversity. Many small-scale torrential rivers and water reaches contribute to the species pool of all the major rivers by converging downstream. These reaches are most likely to be degraded at a faster rate as compared to the large-scale rivers following an increased rate of urbanization, habitat alterations, and changing climatic conditions. Therefore, this study aims to explore River Murti, which is a representative small scale river system characterized by a large altitudinal gradient and a diverse watershed area. Ichthyofaunal diversity (i.e., diversity, evenness & richness) and 21 environmental variables are measured through a tri-seasonal sampling effort conducted along 14 selected locations. A total of 41 fish species (including species belonging to 4 Near Threatened, 8 Vulnerable, and 1 Endangered) are found inhabiting this river. Ichthyofaunal assemblage is found to be primarily modulated by habitat diversity and landscape variables. Three Aquatic Ecological Systems (AES) have been identified along this river in a top-down approach based on recorded environmental variables. We have calculated an observed/expected ratio for each diversity indices along 14 locations based on predicted temporal variability using boosted regression (BRT) models. The evaluation of diversity status has been kept at 0.5 to account for a 50% loss or deviation from observed (O/E50). This evaluation has been successfully used to delineate AES1 with majorly “Impaired” status and thus ensures its importance in terms of species conservation. Our study indicates the contribution of 11 major environmental drivers modulating the species assemblage patterns in these AES. Amongst them, altitude, substrate coarseness, river morphology, and shelter availability are strongly associated with species diversity as per the BRT models. These underlying factors are also correlated with “basin pressure,” suggesting that anthropogenic disturbances, as well as the changing climate, might play an important role in the gradual change in environmental conditions, which in turn could cause a shift in species assemblage structure.  相似文献   

复杂地形景区三维导览图的设计与实现     

吴思锴  李百寿  郭家豪  李雪  张卫平 《北京测绘》2020,(1):38-43

为满足复杂地形景区对三维地图导览的需求,构建更为清晰的三维地图模型,提供良好的三维导览地图设计方案显得尤为重要。为了更好地与卫星影像进行贴合,DEM数据的采样密度要与卫星影像的分辨率一致。本文通过对比当下常用的四种空间插值方法的适用范围与运用特点,设置相关阈值及权重,直观比较了四种插值方法产生的插值结果,选择更适合复杂景区DEM插值的插值方法并对其进行精度提升,以此得到符合精度要求的DEM数据。最后利用相应地区的卫星影像进行地图投影及影像贴图,两种数据结合构建复杂景区的三维地图模型,给游客带来更为精确直观的定位信息和空间要素信息。  相似文献   

利用模板匹配技术检测米尺度岩石断层黏滑实验中的声发射事件   总被引：1，自引：0，他引：1       下载免费PDF全文

侯金欣  谢凡  任雅琼  王宝善 《地球物理学报》2020,63(4):1630-1641

声发射观测是岩石摩擦实验中研究强震孕育机制的重要观测手段之一.传统的声发射观测以触发记录为主,难以捕捉并提取微弱的声发射信号.近年来天然地震学中发展的模板匹配技术可以在连续波形记录中识别出微弱的事件,大大提升事件检测能力.本文发展了适用于多通道连续记录的声发射信号的模板匹配技术,并将该技术应用于分析米尺度岩石断层黏滑失稳过程.研究结果显示:模板匹配技术识别出的声发射数量约为传统方法识别的5倍,相对完备震级降低约0.3.临近失稳,检测目录完备震级以上声发射率表现出幂律增加的特征,且声发射事件聚集在失稳破裂起始点附近.失稳后,检测目录完备震级以上声发射率表现出幂律衰减,其中失稳后早期表现出较慢的衰减速度.另外,失稳后早期声发射事件表现出随对数时间沿断层迁移的趋势.最后,通过与天然地震学观测的结果对比表明,声发射模板匹配识别技术是研究大尺度岩石摩擦滑动失稳过程中前震和余震时空演化规律的有效手段,该技术助于在方法上为室内实验和野外观测进行融合研究提供思路.  相似文献   

黄土高原沟谷地貌发育演化研究进展与展望     

熊礼阳  汤国安 《地球信息科学学报》2020,22(4):816-826

黄土沟谷是黄土地貌中最有活力、最具变化、最富特色的对象单元,黄土高原千沟万壑的地貌形态以及触目惊心的侵蚀状态也让区域内沟谷地貌的形成、发育及演化问题成为研究中焦点及前沿性科学问题。近年来,诸多学者采用地学测年法、特征表达法、监测模拟法力图实现对黄土沟谷发育演化进程中“过去-现代-未来”的科学认知。这些研究在相当程度上丰富了黄土沟谷发育过程的认知。本文梳理了黄土高原沟谷地貌演化相关研究的现状,并从黄土高原地貌演化、黄土沟谷发育、基于DEM的沟谷信息提取与表达等研究进行了系统的回顾、梳理与分析。此外,本文提出“黄土沟道剖面群组”概念与方法,试图从新的视角审视黄土沟谷地貌发育演化过程。沟道剖面在黄土沟谷发育演化进程中传递物质能量和累积地形动力,并通过径流节点的串联实现剖面群的连接与组合,形成独特的剖面“群组”模式;该沟道剖面群组是集黄土沟谷地貌特征与过程于一体的综合信息集成体,其三维空间结构是对黄土沟谷地貌发育演化的高度抽象与映射,并可望进一步丰富黄土高原数字地形分析理论与方法体系,为黄土高原黄土地貌成因机理与空间分异格局带来创新的认识。  相似文献   

极端条件下心墙泥浆料的渗透反滤试验研究     

左永振  赵娜 《岩土力学》2020,41(2):520-526

高土石心墙坝的渗透稳定性在很大程度上依赖于反滤层对心墙料的反滤保护作用。心墙在大坝蓄水和长期运行的条件下，要经历复杂的填筑加载、浸水饱和与水荷载的作用，在差异沉降、复杂结构应力作用、水力劈裂和渗透水流作用下，心墙一旦出现裂缝，其渗透稳定性及反滤层的保护作用就将面临严峻的考验。针对这一问题，设计了专门非常规的抛填土料反滤试验和泥浆渗透反滤试验，模拟心墙裂缝条件下其颗粒被冲刷起动后，被反滤料阻挡和淤积过程。试验结果表明，心墙料和反滤料满足反滤准则条件下，心墙颗粒被拦截和淤积在反滤层上游表面，反滤料能有效防止心墙颗粒的流失，反滤层在极端条件下对心墙料仍能起到有效的反滤保护作用。  相似文献   

Robust adaptive unscented Kalman filter for bearings-only tracking in three dimensional case     

《Applied Ocean Research》2019

This paper proposes an improved version of Unscented Kalman Filter (UKF), namely Robust Adaptive UKF (RAUKF), with a special focus on Bearings-Only Target Tracking for three-dimensional case (3DBOT). The automatic tuning of the noise covariance matrices and the robust estimation of the target states form a critical point for the performance of the Kalman-type filtering algorithms, especially in the variable environmental conditions exposed in underwater. The key idea of the proposed filter is to combine robust aspects of UKF and adaption of the process and measurement noise covariance matrices with low computational complexity. The main contribution of this paper is to adjust these matrices by means of the steepest descent algorithm, and the H_∞ technique is embedded to achieve superior performance in terms of accuracy and robustness against initial conditions and model uncertainties. Different experiments are performed to evaluate the performance of the proposed algorithm in the 3DBOT problem with a single moving observer. Simulations demonstrate that the proposed filter produce more accurate results with satisfactory computational burden in comparison with other methods.  相似文献   

应用经验正交函数估算顶部电离层电子密度剖面          下载免费PDF全文

王林  万卫星  乐新安  任志鹏  佘承莉 《地球物理学报》2019,62(5):1582-1590

本文基于IRI模型、地面数字测高仪和GNSS TEC数据,提出了一种利用经验正交函数(Empirical Orthogonal Function,简称EOF)估算顶部电离层电子密度剖面的方法,并将其应用于美国Millstone Hill测高仪和GNSS数据以估算顶部电离层电子密度剖面.通过将估算的临界频率、峰值高度、400km以上电子密度分别与测高仪实测临界频率、测高仪实测峰值高度以及非相干散射雷达实测400km以上电子密度作对比以对方法的有效性进行验证.统计结果显示估算临界频率、峰值高度与测高仪实测数据基本一致,400km以上估算电子密度相较于非相干散射雷达实测的绝对误差平均值仅是测高仪推算400km以上电子密度绝对误差平均值的一半左右.所以本文提出的方法可以更加精确地估算顶部电离层电子密度.  相似文献   

Structure of residual oil as a function of wettability using pore-network modelling     

《Advances in water resources》2014

In the water flooding of mixed-wet porous media, oil may drain down to relatively low residual oil saturations (S_or). Various studies have indicated that such low saturations can only be reached when oil layers in pore corners are included in the pore-scale modelling. These processes within a macroscopic porous medium can be modelled at the pore-scale by incorporating the fundamental physics of capillary dominated displacement within idealised pore network models. Recently, the authors have developed thermodynamic criteria for oil layer existence in pores with non-uniform wettability which takes as input geometrically and topologically representative networks, to calculate realistic S_or values for mixed-wet and oil-wet sandstones [16, 21]. This previous work is developed in this paper to include (i) the visualisation of the 3D structure of this residual oil, and (ii) a statistical analysis of this “residual/remaining” oil. Both the visualisation and the statistical analysis are done under a wide range of wettability conditions, which is reported for the first time in this paper.The structure of residual oil for strongly water wet systems is well known (where residual = remaining oil) and our model agrees with this but this structure changes radically for mixed wet systems (where residual ≠ remaining) and this has not yet been visualised experimentally. We find that for more water-wet systems high final residual oil saturations are reached at relatively small amounts of water injected and this oil is present in the pores as bulk oil. On the other hand, for more oil-wet systems we find a slow decrease of the amount of remaining oil with increasing amounts of injected water. During the process, the remaining connectivity of the oil phase is increasingly provided by oil layers only, hence the slow drainage. The final residual oil saturation, only reached in the theoretical limit of an infinite amount of injected water, is almost entirely contained in large number of (relatively low volume) oil layers, which are present in pores of most radius sizes.  相似文献