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为了提高GPS观测点大地高转换为正常高的精度,充分利用GPS观测数据中的高程信息,提出用GPS控制网进行高程拟合模型,以获得高精度的正常高,其结果可以替代四等水准,这为水准实施困难区域高程控制测量提出了一种新模式。 相似文献
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为了提高GPS观测点大地高转换为正常高的精度,充分利用GPS观测数据中的高程信息,提出用GPS控制网进行高程拟合模型,以获得高精度的正常高,其结果可以替代四等水准,这为水准实施困难区域高程控制测量提出了一种新模式. 相似文献
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利用数学模型拟合似大地水准面求定高精度的高程异常值,将GPS大地高转换为正常高,是目前GPS高程测量的研究热点。阐述克里格(Kriging)法、基于多项式曲面的Kriging法和基于小波分析的Kriging法用于GPS高程拟合的基本原理,并以GPS控制网实测数据为例进行对比试验研究。结果表明,基于Kriging法的综合模型拟合精度优于单一的Kriging法拟合精度,基于小波分析的Kriging法用于GPS高程拟合的精度最高。 相似文献
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根据库区GPS控制网大地高与二等水准、四等三角高程,采用最小二乘法原理,建立平面模型、二次曲面模型、三次曲面模型,求得较高精度高程异常,在GPS测量得到平面位置的同时,获得工程中使用的正常高程。通过对平面模型、二次曲面模型和三次曲面模型比较分析,说明在山区二次曲面模型就能够满足一定等级高程测量精度要求。在水电工程河谷流域采用GPS拟合高程,能够减轻劳动强度,提高工效。 相似文献
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工程测量时,必须将GPS定位技术获得的大地高转换成正常高。根据带状工程测量控制点高程异常(大地高与正常高差值)序列的特点,提出了以高程异常序列为行为主因素,以控制点的坐标按多项式展开后的系数构成控制点的位置因素为原因量子序列,在不考虑高程异常序列的导数变化率时,可用静态灰模型GM(0,h)进行GPS大地高向正常高的转换。通过高山区公路高程控制测量实例计算,说明该方法转换精度明显优于常用的函数模型拟合法。特别是当测区内GPS控制点与水准点较少时,该方法比传统的函数模型拟合法转换更具有明显的优势,可以推广应用于其他带状工程GPS大地高向正常高的转换。 相似文献
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GPS高程综合模型应用研究 总被引:1,自引:0,他引:1
GPS高程的多种逼近模型有其使用的条件和范围,为进一步提高GPS高程的转换精度,提出了GPS高程转换二次曲面拟合的加权平均模型和基于神经网络的综合逼近模型。通过实测的GPS水准数据对综合模型和几种单一模型进行分析比较,结果表明综合模型逼近高程的精度和可靠性均高于单一模型。 相似文献
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随着GNSS技术及高精度、高分辨率全球重力模型发展,利用GNSS测得的大地高向正常高转换精度得到极大提高,可以实现山区河道高精度三维坐标测量。以金沙江流域某水电站为例,利用测区已有高等级GNSS/水准控制点及EGM 96、不同分辨率EGM 2008模型进行GNSS大地高向正常高转换,与三角高程施测的四等高程点比较并进行精度分析。经证实,利用EMG 2008在山区河道高程转换中误差约±5cm,可满足图根测量精度等级要求。利用EMG2008进行高程转换可极大提高工作效率,在测区求取坐标转换七参数,可实现高精度GNSS三维坐标测量,满足工程测量需求。 相似文献
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GPS获得垂直分量是基于参考椭球的大地高,与工程中需要的正常高有一差值,即高程异常。而由于大地水准面的不规则性,使GPS获得的垂直信息使用受到了限制。进行GPS高程拟合,通过已知点的高程异常值推求未知点的高程异常值,进而求得未知点的正常高是目前转换GPS高程的主要方法。文章结合工程实例和实验数据,比较GPS曲面拟合高程与几何水准高程,探讨总结了GPS高程曲面拟合模型的应用方法和精度问题,提出了水利水电工程高程控制测量工作应该注意的问题及作业精度。 相似文献
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根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。 相似文献
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The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects. 相似文献
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In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment. 相似文献
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V. K. Konovalov O. V. Yashkin V. V. Ermakov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2008,42(2):105-109
A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed
in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash
and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers
of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional
components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect
dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system,
configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants
of dry ash utilization and the advantages of producing of size-separated particles are considered.
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Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008). 相似文献
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Peter B. Bayley 《河流研究与利用》1991,6(2):75-86
The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed. 相似文献
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We tested the recolonization of the phytobenthic community in the tailwaters of Glen Canyon Dam following long- and short-term experimentally induced desiccation. The response of Cladophora glomerata, Oscillatoria spp., miscellaneous phytobenthos species and periphyton was studied over 18 weeks using three treatments: (1) undisturbed control cobbles from the submerged zone; (2) cobbles desiccated and replaced into the submerged zone; and (3) cobbles desiccated and replaced into the varial zone. Periphyton density and compositional response resulting from these treatments were also examined. Desiccation treatments were significantly different in biomass from controls throughout the study. The biomass of desiccated and replaced river cobbles averaged <30% of the controls for C. glomerata and periphyton during the 18-week recolonization period. In contrast, the biomass of the control Oscillatoria and miscellaneous phytobenthos species averaged only 3 and 50% of that in the desiccation treatments, respectively. Cladophora, the dominant alga, comprised 77% of the phytobenthic biomass. A significant positive relationship between discharge, Cladophora and periphyton biomass was present in all treatments, while there was a negative relationship with discharge for Oscillatoria and miscellaneous phytobenthos species. There was a significant inverse correlation, as well as a pattern of separate biomass dominance, between C. glomerata and Oscillatoria. Cladophora was the dominant phytobenthos species on cobbles below the baseflow and Oscillatoria was dominant on cobbles in the varial zone. In general, the Cladophora biomass decreased under intermittent drying conditions, while Oscillatoria declined under permanently wet conditions. Diatom composition was not significantly different between treatments; however, their density was lower on desiccated cobbles. Diatom density on desiccated cobbles in the submerged and varial zones averaged 69 and 42% of that of the controls, respectively. Recovery and maintenance of benthic resources are hindered by fluctuating flow regimes driven by electricity and irrigation requirements. Repeated desiccation of the phytobenthos has major effects on the bottom-up interactions in the Colorado River ecosystem. © 1998 John Wiley & Sons, Ltd. 相似文献