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Incorrect modeling of troposphere delays is one of the major error sources for space geodetic techniques such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). Over the years, many approaches have been devised which aim at mapping the delay of radio waves from zenith direction down to the observed elevation angle, so-called mapping functions. This paper contains a new approach intended to refine the currently most important discrete mapping function, the Vienna Mapping Functions 1 (VMF1), which is successively referred to as Vienna Mapping Functions 3 (VMF3). It is designed in such a way as to eliminate shortcomings in the empirical coefficients b and c and in the tuning for the specific elevation angle of \(3^{\circ }\). Ray-traced delays of the ray-tracer RADIATE serve as the basis for the calculation of new mapping function coefficients. Comparisons of modeled slant delays demonstrate the ability of VMF3 to approximate the underlying ray-traced delays more accurately than VMF1 does, in particular at low elevation angles. In other words, when requiring highest precision, VMF3 is to be preferable to VMF1. Aside from revising the discrete form of mapping functions, we also present a new empirical model named Global Pressure and Temperature 3 (GPT3) on a \(5^{\circ }\times 5^{\circ }\) as well as a \(1^{\circ }\times 1^{\circ }\) global grid, which is generally based on the same data. Its main components are hydrostatic and wet empirical mapping function coefficients derived from special averaging techniques of the respective (discrete) VMF3 data. In addition, GPT3 also contains a set of meteorological quantities which are adopted as they stand from their predecessor, Global Pressure and Temperature 2 wet. Thus, GPT3 represents a very comprehensive troposphere model which can be used for a series of geodetic as well as meteorological and climatological purposes and is fully consistent with VMF3. 相似文献
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J. Kouba 《Journal of Geodesy》2008,82(4-5):193-205
The new gridded Vienna Mapping Function (VMF1) was implemented and compared to the well-established site-dependent VMF1, directly
and by using precise point positioning (PPP) with International GNSS Service (IGS) Final orbits/clocks for a 1.5-year GPS
data set of 11 globally distributed IGS stations. The gridded VMF1 data can be interpolated for any location and for any time
after 1994, whereas the site-dependent VMF1 data are only available at selected IGS stations and only after 2004. Both gridded
and site-dependent VMF1 PPP solutions agree within 1 and 2 mm for the horizontal and vertical position components, respectively,
provided that respective VMF1 hydrostatic zenith path delays (ZPD) are used for hydrostatic ZPD mapping to slant delays. The
total ZPD of the gridded and site-dependent VMF1 data agree with PPP ZPD solutions with RMS of 1.5 and 1.8 cm, respectively.
Such precise total ZPDs could provide useful initial a priori ZPD estimates for kinematic PPP and regional static GPS solutions.
The hydrostatic ZPDs of the gridded VMF1 compare with the site-dependent VMF1 ZPDs with RMS of 0.3 cm, subject to some biases
and discontinuities of up to 4 cm, which are likely due to different strategies used in the generation of the site-dependent
VMF1 data. The precision of gridded hydrostatic ZPD should be sufficient for accurate a priori hydrostatic ZPD mapping in
all precise GPS and very long baseline interferometry (VLBI) solutions. Conversely, precise and globally distributed geodetic
solutions of total ZPDs, which need to be linked to VLBI to control biases and stability, should also provide a consistent
and stable reference frame for long-term and state-of-the-art numerical weather modeling. 相似文献
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Sources of errors in the precise leveling influencing the results of measurements especially strongly in mountains are considered
in this study. Data are given on new error sources, including (1) the difference in temperatures of invar bands of rods and
of the air; and (2) displacements of rock bench marks during diurnal variations in temperature of rocks. The ranges of possible
total systematic error in leveding are estimated. 相似文献
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为了获得形式多样的地形可视化效果,投影方式的选择至关重要,通过对正投影、透视投影、渐进式投影和平斜投影等多种投影方式的原理与方法进行研究,分析了各种投影方式的适用性及其获得的地形可视化效果,为应用实践提供了有益借鉴。 相似文献
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This paper compares estimates of station coordinates from global GPS solutions obtained by applying different troposphere
models: the Global Mapping Function (GMF) and the Vienna Mapping Function 1 (VMF1) as well as a priori hydrostatic zenith
delays derived from the Global Pressure and Temperature (GPT) model and from the European Centre for Medium-Range Weather
Forecasts (ECMWF) numerical weather model data. The station height differences between terrestrial reference frames computed
with GMF/GPT and with VMF1/ECMWF are in general below 1 mm, and the horizontal differences are even smaller. The differences
of annual amplitudes in the station height can also reach up to 1 mm. Modeling hydrostatic zenith delays with mean (or slowly
varying empirical) pressure values instead of the true pressure values results in a partial compensation of atmospheric loading.
Therefore, station height time series based on the simple GPT model have a better repeatability than those based on more realistic
ECMWF troposphere a priori delays if atmospheric loading corrections are not included. On the other hand, a priori delays
from numerical weather models are essential to reveal the full atmospheric loading signal. 相似文献
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The anisotropy of propagation of radio waves used by global navigation satellite systems is investigated using high-resolution
observational data assimilations produced by the European Centre for Medium-range Weather Forecast. The geometry and the refractivity
of the neutral atmosphere are built introducing accurate geodetic heights and continuous formulations of the refractivity
and its gradient. Hence the realistic ellipsoidal shape of the refractivity field above the topography is properly represented.
Atmospheric delays are obtained by ray-tracing through the refractivity field, integrating the eikonal differential system.
Ray-traced delays reveal the anisotropy of the atmosphere. With the aim to preserve the classical mapping function strategy,
mapping functions can evolve to adapt to high-frequency atmospheric fluctuations and to account for the anisotropy of propagation
by fitting at each site and time the zenith delays and the mapping functions coefficients. Adaptive mapping functions (AMF)
are designed with coefficients of the continued fraction form which depend on azimuth. The basic idea is to expand the azimuthal
dependency of the coefficients in Fourier series introducing a multi-scale azimuthal decomposition which slightly changes
the elevation functions with the azimuth. AMF are used to approximate thousands of atmospheric ray-traced delays using a few
tens of coefficients. Generic recursive definitions of the AMF and their partial derivatives lead to observe that the truncation
of the continued fraction form at the third term and the truncation of the azimuthal Fourier series at the fourth term are
sufficient in usual meteorological conditions. Delays’ and elevations’ mapping functions allow to store and to retrieve the
ray-tracing results to solve the parallax problem at the observation level. AMF are suitable to fit the time-variable isotropic
and anisotropic parts of the ray-traced delays at each site at each time step and to provide GPS range corrections at the
measurement level with millimeter accuracy at low elevation. AMF to the azimuthal anisotropy of the neutral atmosphere are
designed to adapt to complex weather conditions by adaptively changing their truncations. 相似文献
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随着计算机技术与测绘科学技术的发展,传统的模拟测图方法已被高度自动化的数字化测图技术所替代。通过大量实践探索,提出一种在测量中实用、经济、高效的测图方法一一简码法,并通过C#语言编程将野外测点简码转化成CASS成图系统默认的编程实现野外数据的转换,并实现内业自动成图。文中利用该方法对昆明理工大学校园进行了数字化测图验证。结果表明:该方法相对其他测图方法外业数据采集速度更快,内业工作量及测量成本大大减少,且该方法能方便地与GIS系统进行数据交换以及更好地服务于测绘行业,提高工作效率。 相似文献
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The troposphere delay is an important source of error for precise GNSS positioning due to its high correlation with the station height parameter. It has been demonstrated that errors in mapping functions can cause sub-annual biases as well as affect the repeatability of GNSS solutions, which is a particular concern for geophysical studies. Three-dimensional ray-tracing through numerical weather models (NWM) is an excellent approach for capturing the directional and daily variation of the tropospheric delay. Due to computational complexity, its use for positioning purposes is limited, but it is an excellent tool for evaluating current state-of-the-art mapping functions used for geodetic positioning. Many mapping functions have been recommended in the past such as the Niell Mapping Function (NMF), Vienna Mapping Function 1 (VMF1), and the Global Mapping Function (GMF), which have been adopted by most IGS analysis centers. A new Global Pressure Temperature model (GPT2) has also been developed, which has been shown to improve upon the original atmospheric model used for the GMF. Although the mapping functions mentioned above use the same functional formulation, they vary in terms of their atmospheric source and calibration approach. A homogeneous data set of three-dimensional ray-traced delays is used to evaluate all components of the mapping functions, including their underlying functional formulation, calibration, and compression method. Additionally, an alternative representation of the VMF1 is generated using the same atmospheric source as the truth data set to evaluate the differences in ray-tracing methods and their effect on the end mapping function. The results of this investigation continue to support the use of the VMF1 as the mapping function of choice when geodetic parameters are of interest. Further support for the GPT2 and GMF as reliable back-ups when the VMF1 is not available was found due to their high consistency with the NWM-derived mapping function. Additionally, a small latitude-dependent bias in station height was found in the current mapping functions. This bias was identified to be due to the assumption of a constant radius of the earth and was largest at the poles and at the equator. Finally, an alternative version of the VMF1 is introduced, namely the UNB-VMF1 which provides users with an independent NWM-derived mapping function to support geodetic positioning. 相似文献
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北京1号小卫星多光谱影像全国镶嵌技术与制图研究 总被引:2,自引:0,他引:2
北京1号小卫星在轨运行一年多成功接收了覆盖中国各个行政区域的多光谱影像数据,为全国数字镶嵌图的研究提供了丰富的数据资料.针对北京1号小卫星特点进行关键技术和方法研究,形成了北京1号小卫星多光谱影像全国范围数据获取任务测控优化模式,解决了北京1号小卫星多光谱数据预处理中去条带、波段自动配准、MTF复原处理等关键技术,系统地、全面地阐述了全国镶嵌图制作的技术流程和方法. 相似文献
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基于可拓学的测绘项目风险管理 总被引:1,自引:0,他引:1
本文介绍了风险管理的基本理论,分析了目前传统测绘项目在风险管理方面存在的不足.同时,针对测绘项目实施时如何进行有效的风险管理的难题,提出了基于可拓学的测绘项目风险管理方法.实证研究结果表明此方法合理、可行、操作简单,具有很强的实用性. 相似文献
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针对导航卫星钟差预报精度不高的问题,该文引入了GM-LSSVM钟差预报模型,采用全局寻优能力较强的遗传算法对模型的参数选取过程进行优化,避免模型陷入局部最优,从而改善了组合模型中惩罚因子和核函数参数选择的盲目性。最后选取国际GPS服务组织提供的卫星钟差数据,分别建立GM(1,1)模型、LSSVM模型、GM-LSSVM模型和遗传算法优化的GM-LSSVM模型进行短期钟差预报分析和仿真实验。仿真结果表明,优化后的模型预报精度小于1.3ns,精度比前3种模型提高了45%~60%,符合钟差预报的要求。 相似文献