共查询到20条相似文献，搜索用时 78 毫秒
1.
The correction of tropospheric influences via so-called path delays is critical for the analysis of observations from space geodetic techniques like the very long baseline interferometry (VLBI). In standard VLBI analysis, the a priori slant path delays are determined using the concept of zenith delays, mapping functions and gradients. The a priori use of ray-traced delays, i.e., tropospheric slant path delays determined with the technique of ray-tracing through the meteorological data of numerical weather models (NWM), serves as an alternative way of correcting the influences of the troposphere on the VLBI observations within the analysis. In the presented research, the application of ray-traced delays to the VLBI analysis of sessions in a time span of 16.5 years is investigated. Ray-traced delays have been determined with program RADIATE (see Hofmeister in Ph.D. thesis, Department of Geodesy and Geophysics, Faculty of Mathematics and Geoinformation, Technische Universität Wien. http://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-3444, 2016) utilizing meteorological data provided by NWM of the European Centre for Medium-Range Weather Forecasts (ECMWF). In comparison with a standard VLBI analysis, which includes the tropospheric gradient estimation, the application of the ray-traced delays to an analysis, which uses the same parameterization except for the a priori slant path delay handling and the used wet mapping factors for the zenith wet delay (ZWD) estimation, improves the baseline length repeatability (BLR) at 55.9% of the baselines at sub-mm level. If no tropospheric gradients are estimated within the compared analyses, 90.6% of all baselines benefit from the application of the ray-traced delays, which leads to an average improvement of the BLR of 1 mm. The effects of the ray-traced delays on the terrestrial reference frame are also investigated. A separate assessment of the RADIATE ray-traced delays is carried out by comparison to the ray-traced delays from the National Aeronautics and Space Administration Goddard Space Flight Center (NASA GSFC) (Eriksson and MacMillan in http://lacerta.gsfc.nasa.gov/tropodelays, 2016) with respect to the analysis performances in terms of BLR results. If tropospheric gradient estimation is included in the analysis, 51.3% of the baselines benefit from the RADIATE ray-traced delays at sub-mm difference level. If no tropospheric gradients are estimated within the analysis, the RADIATE ray-traced delays deliver a better BLR at 63% of the baselines compared to the NASA GSFC ray-traced delays. 相似文献
2.
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
3.
Cuixian Lu Xingxing Li Florian Zus Robert Heinkelmann Galina Dick Maorong Ge Jens Wickert Harald Schuh 《Journal of Geodesy》2017,91(9):1019-1029
Precise positioning with the current Chinese BeiDou Navigation Satellite System is proven to be of comparable accuracy to the Global Positioning System, which is at centimeter level for the horizontal components and sub-decimeter level for the vertical component. But the BeiDou precise point positioning (PPP) shows its limitation in requiring a relatively long convergence time. In this study, we develop a numerical weather model (NWM) augmented PPP processing algorithm to improve BeiDou precise positioning. Tropospheric delay parameters, i.e., zenith delays, mapping functions, and horizontal delay gradients, derived from short-range forecasts from the Global Forecast System of the National Centers for Environmental Prediction (NCEP) are applied into BeiDou real-time PPP. Observational data from stations that are capable of tracking the BeiDou constellation from the International GNSS Service (IGS) Multi-GNSS Experiments network are processed, with the introduced NWM-augmented PPP and the standard PPP processing. The accuracy of tropospheric delays derived from NCEP is assessed against with the IGS final tropospheric delay products. The positioning results show that an improvement in convergence time up to 60.0 and 66.7% for the east and vertical components, respectively, can be achieved with the NWM-augmented PPP solution compared to the standard PPP solutions, while only slight improvement in the solution convergence can be found for the north component. A positioning accuracy of 5.7 and 5.9 cm for the east component is achieved with the standard PPP that estimates gradients and the one that estimates no gradients, respectively, in comparison to 3.5 cm of the NWM-augmented PPP, showing an improvement of 38.6 and 40.1%. Compared to the accuracy of 3.7 and 4.1 cm for the north component derived from the two standard PPP solutions, the one of the NWM-augmented PPP solution is improved to 2.0 cm, by about 45.9 and 51.2%. The positioning accuracy for the up component improves from 11.4 and 13.2 cm with the two standard PPP solutions to 8.0 cm with the NWM-augmented PPP solution, an improvement of 29.8 and 39.4%, respectively. 相似文献
4.
对流层映射函数是将对流层天顶延迟转化为信号传播路径上总延迟的重要模型,选择合适的映射函数对反演大气可降水量(PWV)精度的提高具有十分重要的意义．本文研究了对流层映射函数对反演PWV精度的影响,选取VMF1、GMF、NMF 3种映射函数,利用GAMIT解算比较3种映射函数在不同季节、不同高度角对网基线解算以及反演PWV的精度影响．结果表明,在进行PWV反演时,选择10°高度角作为解算截止高度角的GMF函数模型反演精度最佳,为进一步提高GNSS水汽反演的实时精度提供了参考． 相似文献
5.
受实测气象参数的限制，使用标准大气参数的传统对流层模型的精度并不高；使用参数估计法的精密对流层模型增加了观测方程的待估参数，影响收敛速度. 针对实测气象参数缺失的情况，提出一种融合对流层模型，使用两种非实测气象参数模型分别计算出平均海平面处和测站处的气象参数，再利用Saastamoinen模型经验公式求解天顶对流层延迟（ZTD）. 利用RTKLIB软件进行精密单点定位（PPP）实验. 提出的融合对流层模型摆脱了实测气象参数的限制，解算结果表明:使用该模型时，在东、北、天方向的定位精度分别比Saastamoinen模型提高16 mm、1 mm、2.2 mm，比MOPS模型提高13.8 mm、0.7 mm、1.6 mm，比GPT/UNB3m+Sa模型提高2.9 mm、0.4 mm、0.7 mm，在天、北方向的定位精度接近参数估计模型，实现了PPP定位精度的提高. 相似文献
6.
Assessment of ECMWF-derived tropospheric delay models within the EUREF Permanent Network 总被引：1，自引：0，他引：1
The Global Positioning System (GPS) observations from the EUREF Permanent Network (EPN) are routinely analyzed by the EPN
analysis centers using a tropospheric delay modeling based on standard pressure values, the Niell Mapping Functions (NMF),
a cutoff angle of 3° and down-weighting of low elevation observations. We investigate the impact on EPN station heights and
Zenith Total Delay (ZTD) estimates when changing to improved models recommended in the updated 2003 International Earth Rotation
and Reference Systems Service (IERS) Conventions, which are the Vienna Mapping Functions 1 (VMF1) and zenith hydrostatic delays
derived from numerical weather models, or the empirical Global Mapping Functions (GMF) and the empirical Global Pressure and
Temperature (GPT) model. A 1-year Global Positioning System (GPS) data set of 50 regionally distributed EPN/IGS (International
GNSS Service) stations is processed. The GPS analysis with cutoff elevation angles of 3, 5, and 10° revealed that changing
to the new recommended models introduces biases in station heights in the northern part of Europe by 2–3 mm if the cutoff
is lower than 5°. However, since large weather changes at synoptic time scales are not accounted for in the empirical models,
repeatability of height and ZTD time series are improved with the use of a priori Zenith Hydrostatic Delays (ZHDs) derived
from numerical weather models and VMF1. With a cutoff angle of 3°, the repeatability of station heights in the northern part
of Europe is improved by 3–4 mm. 相似文献
7.
In the precise point positioning(PPP),some impossible accurately simulated systematic errors still remained in the GPS observations and will inevitably degrade the precision of zenith tropospheric delay(ZTD) estimation.The stochastic models used in the GPS PPP mode are compared.In this paper,the research results show that the precision of PPP-derived ZTD can be obviously improved through selecting a suitable stochastic model for GPS measurements.Low-elevation observations can cover more troposphere informat... 相似文献
8.
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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10.
基于非差非组合PPP-RTK的大气改正模型及其性能验证 总被引：2，自引：3，他引：2
高精度的大气改正是加快PPP-RTK收敛的重要前提。本文以区域跟踪网台站数据为基础,基于非差非组合PPP提取斜路径电离层和天顶对流层延迟,作为PPP-RTK大气建模的数据源。电离层延迟采用基于斜路径星间单差的改正模型,对流层采用非差天顶对流层模型,设计了相关的服务端和用户端软件系统。在系统设计上,通过服务端提取数据构建大气模型并播发,用户端接收参数并用于实时PPP-RTK定位。对上海区域进行服务端和用户端的试验,服务端计算的参数表明：GPS、GALILEO、BDS系统的电离层、对流层模型内符合精度为6~7 mm。用户端的646组PPP-RTK伪动态试验表明：水平方向30 s内收敛的占比为89.16%、1 min内收敛的占比为91.80%、2 min内收敛的占比为95.98%;三维方向收敛结果中,上述收敛时间尺度分别占总数的86.22%、88.70%和93.34%。附加大气约束后,模糊度固定率为95.59%,收敛后水平方向和三维方向定位RMSE分别为2.35和4.63 cm。实时动态试验表明,PPP首次固定时间为36 s,水平和三维定位精度分别达到了1.13和3.21 cm。 相似文献
11.
由于高纬度地区气温气压值及变化率与中低纬度地区有较大差异,因此目前发布的多种对流层延迟模型在高纬度地区使用的精度会不同。为了给高纬度地区BDS/GPS用户提供更好的对流层延迟模型选择,文中采用UNB3,EGNOS和GPT2模型,以IGS发布的ZPD产品和SINEX文件作为参考,对比基于这三种对流层延迟模型计算的天顶对流层总延迟量以及精密单点定位精度,可知GPT2较UNB3和EGNOS在高纬度地区定位中有更好的精度表现。 相似文献
12.
Forecast Vienna Mapping Functions 1 for real-time analysis of space geodetic observations 总被引：3，自引：2，他引：1
The Vienna Mapping Functions 1 (VMF1) as provided by the Institute of Geodesy and Geophysics (IGG) at the Vienna University
of Technology are the most accurate mapping functions for the troposphere delays that are available globally and for the entire
history of space geodetic observations. So far, the VMF1 coefficients have been released with a time delay of almost two days;
however, many scientific applications require their availability in near real-time, e.g. the Ultra Rapid solutions of the
International GNSS Service (IGS) or the analysis of the Intensive sessions of the International VLBI Service (IVS). Here we
present coefficients of the VMF1 as well as the hydrostatic and wet zenith delays that have been determined from forecasting
data of the European Centre for Medium-Range Weather Forecasts (ECMWF) and provided on global grids. The comparison with parameters
derived from ECMWF analysis data shows that the agreement is at the 1 mm level in terms of station height, and that the differences
are larger for the wet mapping functions than for the hydrostatic mapping functions and the hydrostatic zenith delays. These
new products (VMF1-FC and hydrostatic zenith delays from forecast data) can be used in real-time analysis of geodetic data
without significant loss of accuracy. 相似文献
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16.
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
17.
针对现有对流层天顶延迟模型改正法因水汽参数难以精确获取所导致的时空分辨率与精度上的不足问题，提出了一种融合WRF（weather research and forecasting model）大气数值模式的对流层天顶延迟估计方法。通过分析WRF模式的数值模拟机理及其数据结构特征，采用直接积分与模型改正相结合的混合计算方式，实现了全球任意位置上小时级的对流层天顶延迟估计。验证结果表明，该方法计算的小时级ZTD再分析值精度为13.6 mm，日均值精度更是可达9.3 mm，比传统模型UNB3m的49.6 mm以及目前标称精度最高模型GPT2w的34.6 mm，精度分别提高了约5倍和3.5倍。在30 h的预报时段内，预报值精度也可达22 mm。无论是ZTD再分析值还是预报值比现有模型的估计值精度均有明显提高。 相似文献
18.
Pierre Bosser Olivier Bock Christian Thom Jacques Pelon Pascal Willis 《Journal of Geodesy》2010,84(4):251-265
This paper investigates the impact of rapid small-scale water vapor fluctuations on GPS height determination. Water vapor
measurements from a Raman lidar are used for documenting the water vapor heterogeneities and correcting GPS signal propagation
delays in clear sky conditions. We use data from four short observing sessions (6 h) during the VAPIC experiment (15 May–15
June 2004). The retrieval of wet delays from our Raman lidar is shown to agree well with radiosonde retrievals (bias and standard
deviation (SD) were smaller than 1 and 2.8 mm, respectively) and microwave radiometers (from two different instruments, bias
was 6.0/−6.6 mm and SD 1.3/3.8 mm). A standard GPS data analysis is shown to fail in accurately reproducing fast zenith wet
delay (ZWD) variations. The ZWD estimates could be improved when mean post-fit phase residuals were removed. Several methodologies
for integrating zenith lidar observations into the GPS data processing are also presented. The final method consists in using
lidar wet delays for correcting a priori the GPS phase observations and estimating a scale factor for the lidar wet delays
jointly with the GPS station position. The estimation of this scale factor allows correcting for a mis-calibration in the
lidar data and provides in the same way an estimate of the Raman lidar instrument constant. The agreement of this constant
with an independent determination using radiosonde data is at the level of 1–4%. The lidar wet delays were derived by ray-tracing
from zenith pointing measurements: further improvement in GPS positioning is expected from slant path lidar measurements that
would properly account for water vapor anisotropy. 相似文献
19.
基于单基站的超长基线定位技术在地壳形变监测、高精度授时等领域具有广泛应用,但仍有诸多因素制约着超长基线解算精度。从观测方程出发,利用单差观测值对长（超长）基线(146～1 724 km)解算中的卫星轨道误差、对流层延迟误差、地球潮汐误差和相位缠绕误差等误差特性进行了详细分析。分析结果表明,当基线小于500 km时广播星历误差可忽略不计;超过500 km时需要采用精密星历,同时需要考虑地球潮汐误差的影响;利用参数估计法同时估计基线两端的天顶对流层延迟误差可获得1～2 cm精度;相位缠绕误差对基线小于2 000 km的解算影响可忽略。基于估计天顶对流层延迟的方法解算了5条长(超长)基线（146 km、491 km、837 km、 1 043 km和1 724 km）。实验结果表明,当基线小于500 km时,采用广播星历可获得水平方向优于0.05 m、高程方向优于0.08 m的定位精度;当基线小于2 000 km时,采用超快速精密星历可获得水平方向优于0.025 m、高程方向优于0.055 m的定位精度。解算的初始收敛时间随着基线长度增加而缩短。 相似文献