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31.
本文简要从地籍测绘施工实际出发,介绍了开发全站仪内存空间进行外业数据采集,将数据传输到微机中,结合瑞得软件进行成图编辑的技术方法。实践证明此方法大大提高了工作效率。 相似文献
32.
E. L. Afraimovich E. A. Kosogorov N. P. Perevalova A. V. Plotnikov 《Journal of Atmospheric and Solar》2001,63(18)
This paper is concerned with the parameters of shock-acoustic waves (SAW) generated during rocket launchings. We have developed the interferometric method for determining SAW parameters (including angular characteristics of the wave vector, and the SAW phase velocity, as well as the direction towards the source) using GPS-arrays. Contrary to the conventional radio-probing techniques, the proposed method provides an estimate of SAW parameters without a priori information about the site and time of a rocket launching. The application of the method is illustrated by a case study of ionospheric effects from launchings of rockets PROTON, SOYUZ and SPACE SHUTTLE from Baikonur and Kennedy Space Center cosmodromes in 1998–2000. In spite of a difference of rocket characteristics, the ionospheric response for all launchings had the character of an N-wave corresponding to the form of a shock wave. The SAW period T is 270–360 s, and the amplitude exceeds the standard deviation of total electron content background fluctuations in this range of periods under quiet and moderate geomagnetic conditions by factors of 2–5 as a minimum. The angle of elevation of the SAW wave vector varies from 30° to 60°, and the SAW phase velocity (900–1200 m/s) approaches the sound velocity at heights of the ionospheric F-region maximum. The position of the SAW source, inferred by neglecting refraction corrections, corresponds to the segment of the rockets path at a distance no less than 200–900 km from the launch pad, and to the rocket flying altitude no less than 100 km. Our data are consistent with the existing view that SAW are generated during a nearly horizontal flight of the rocket with its engine in operation in the acceleration segment of the path at 100–130 km altitudes in the lower atmosphere. 相似文献
33.
文章讨论了秋季(1994年10月)和冬季(1995年1月)在中国西部青海省共和县瓦里关山(36°17′N,100°54′E,海拔3816 m)基准站和中国东北黑龙江省五常县的龙凤山(44°44′N,127°36′E,海拔331 m)及中国东南沿海的浙江省临安县的横畈乡(30°18′N,119°44′E,海拔131 m)两个区域本底站(上述3站均属WMO)所采集的气溶胶样品的质量浓度、可溶性离子浓度的时空分布特征和变化规律。初步得出:气溶胶质量浓度和可溶性离子浓度以临安为最高。其次是龙凤山,而瓦里关山为最低 相似文献
34.
针对探地雷达(GPR)双参数全波形反演中电导率反演精度差、双参数存在串扰现象、反演计算量大、易陷入局部极值等问题.作者将具有多参数调节功能的L-BFGS算法引入到GPR时间域全波形反演中,它避免了对Hessian矩阵的直接存储与精确求解,减小了存储量和计算量.结合参数调节因子的选取,有效减小了同步反演时介电常数与电导率的串扰影响,在不降低介电常数反演精度的前提下,提高电导率参数的反演精度.通过在反演目标函数中加载改进全变差正则化方法,提高了反演的稳定性,使目标体边缘轮廓更加清晰.首先以简单模型为例,对比了单尺度反演与多尺度串行反演策略的优劣,说明多尺度串行反演有利于逐步搜索全局最优解;而开展参数调节因子的选取实验,说明合适的参数调节因子可以有效改善介质电导率的反演精度;测试了不同正则化的反演效果,表明改进全变差正则化能提高反演稳定性,显著降低模型重构误差.最后,分别对含噪合成数据和实测数据进行了反演测试,说明本文提出的多尺度、双参数反演具有较强的鲁棒性,能提供更丰富的信息约束,重构图像界面清晰、反演效果好. 相似文献
35.
Guanabara Bay, in Rio de Janeiro state, is impacted by organic matter, oil and heavy metals. The present study evaluated the total mercury (THg) and methylmercury (MeHg) concentrations and the MeHg to THg ratio (%MeHg) in water samples from different points of the bay and in 245 organisms of three different trophic levels sampled between 1990 and 2000. Dissolved mercury concentration in estuarine water samples ranged from 0.72 to 5.23 ngl(-1). THg and MeHg in mussel, ranging from 11.6 to 53.5 microg THg kg(-1) wet wt. and 4.5-21.0 microg MeHg kg(-1) wet wt., varied according to sampling point and water quality. Planktivorous fish and mussel presented similar MeHg concentrations, meanwhile THg in planktivorous fish were lower than in mussel. Carnivorous fish showed higher THg and MeHg concentrations (199.5 +/- 119.3, 194.7 +/- 112.7 microg kg(-1) wet wt. respectively) than organisms from other feeding habits and lower trophic levels. There was a significant difference in the %MeHg among trophic levels: mussel presented lower MeHg percentage (33%) than planktivorous fish (54%) and carnivorous fish (98%). 相似文献
36.
目前紫外后向散射反演臭氧总量的所有算法,都将云考虑成不透明的Lambertian反射体,并假定云顶有效反照率不随波长的变化而变化.然而本文通过模拟计算发现,由于云散射、瑞利散射、臭氧吸收三种作用的综合结果,云顶的有效反照率是与波长相关的,即使光学厚度比较大的云,辐射也可由云顶继续向下传输,因而会受到云顶以下臭氧吸收的影响.用V7方法进行反演,模拟计算结果表明:云的出现使得云顶以下,特别是云内光程增强,导致紫外波段的臭氧吸收衰减增大,所以反演出的臭氧总量值比真实值偏大,本文称这种现象为“云吸收效应”,并讨论了该效应的影响因子.最后,在辐射传输模拟的基础上建立一套反演算法,大大减弱了“云吸收效应”的影响. 相似文献
37.
Younger Dryas to mid-Holocene environmental history of the lowlands of NW Transylvania, Romania 总被引:2,自引:1,他引:2
Angelica Feurdean Volker Mosbrugger Bogdan P. Onac Victor Polyak Daniel Veres 《Quaternary Research》2007,68(3):364-378
Pollen, micro-charcoal and total carbon analyses on sediments from the Turbuta palaeolake, in the Transylvanian Basin of NW Romania, reveal Younger Dryas to mid-Holocene environmental changes. The chronostratigraphy relies on AMS 14C measurements on organic matter and U/Th TIMS datings of snail shells. Results indicate the presence of Pinus and Betula open woodlands with small populations of Picea, Ulmus, Alnus and Salix before 12,000 cal yr BP. A fairly abrupt replacement of Pinus and Betula by Ulmus-dominated woodlands at ca. 11,900 cal. yr BP likely represents competition effects of vegetation driven by climate warming at the onset of the Holocene. By 11,000 cal yr BP, the woodlands were increasingly diverse and dense with the expansion of Quercus, Fraxinus and Tilia, the establishment of Corylus and the decline of upland herbaceous and shrubs taxa. The marked expansion of Quercus accompanied by Tilia between 10,500 and 8000 cal yr BP could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate. At 10,000 cal yr BP, Corylus spread across the region, and by 8000 cal yr BP it replaced Quercus as a dominant forest constituent, with only little representation of Picea abies. Carpinus became established around 5500 cal yr BP, but it was only a minor constituent in local woodlands until ca. 5000 cal yr BP. Results from this study also indicate that the woodlands in the lowlands of Turbuta were never closed. 相似文献
38.
《国际泥沙研究》2020,35(4):355-364
The scour and deposition pattern around an abutment under constant discharge condition is calculated using a three dimensional (3D) Computational Fluid Dynamics (CFD) model. The Reynolds-Averaged Navier Stokes (RANS) equations are solved in three dimensions using a CFD model. The Level Set Method (LSM) is used for calculation of both free surface and bed topography. The two-equation turbulence model (k-ε and k-ω) is used to calculate the eddy viscosity in the RANS equations. The pressure term in the RANS equations on a staggered grid is modeled using the Chorin's projection method. The 5th order Weighted Essentially Non-Oscillatory (WENO) scheme discretizes the convective term of the RANS equations. The Kovacs and Parker and Dey formulations are used for the reduction in bed shear stress on the sloping bed. The model also used the sandslide algorithm which limits bed shear stress reduction during the erosion process. The numerical model solution is validated against experimental results collected at the Politecnico di Milano, Milan, Italy. Further, the numerical model is tested for performance by varying the grid sizes and key parameters like the space and time discretization schemes. The effect of varying bed porosity has been evaluated. Overall, the free surface is well represented in a realistic manner and bed topography is well predicted using the Level Set Method (LSM). 相似文献
39.
40.
Total electron content processing from GPS observations to facilitate ionospheric modeling 总被引:2,自引:1,他引:1
With the increasing global distribution of high rate dual-frequency global positioning system (GPS) receivers, the production
of a real-time atmospheric constituent definition, total electron content (TEC), has become a beneficial contributor to the
modeling applications used in the assessment of GPS position accuracy and the composition of the ionosphere, plasmasphere,
and troposphere. Historically, TEC measurements have been obtained through post processing techniques to produce the quality
of data necessary for modeling applications with rigorous error estimate requirements. These procedures necessitated the collection
of large volumes of data to address the various abnormalities in the computation of TEC associated with the use of greater
data quality controls and source selection while real-time modeling environments must rely on autonomous controls and filtration
techniques to prevent the production of erroneous model results. In this paper we present methods for processing TEC in real
time, which utilize several procedures including the application of an ionospheric model to automatically perform quality
control on the TEC output and the computational techniques used to address receiver multipath, faulty receiver observations,
cycle-slips, segmented processing, and receiver calibrations. The resulting TEC measurements are provided with rigorous error
estimates validated using the vertical TEC from the Jason satellite mission.
相似文献
Nelson A. BonitoEmail: |