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1.
Local geoid determination combining gravity disturbances and GPS/levelling: a case study in the Lake Nasser area, Aswan, Egypt 总被引：1，自引：0，他引：1
C. C. Tscherning Awar Radwan A. A. Tealeb S. M. Mahmoud M. Abd El-Monum Ramdan Hassan I. El-Syaed K. Saker 《Journal of Geodesy》2001,75(7-8):343-348
The use of GPS for height control in an area with existing levelling data requires the determination of a local geoid and
the bias between the local levelling datum and the one implicitly defined when computing the local geoid. If only scarse gravity
data are available, the heights of new data may be collected rapidly by determining the ellipsoidal height by GPS and not
using orthometric heights. Hence the geoid determination has to be based on gravity disturbances contingently combined with
gravity anomalies. Furthermore, existing GPS/levelling data may also be used in the geoid determination if a suitable general
gravity field modelling method (such as least-squares collocation, LSC) is applied. A comparison has been made in the Aswan
Dam area between geoids determined using fast Fourier transform (FFT) with gravity disturbances exclusively and LSC using
only the gravity disturbances and the disturbances combined with GPS/levelling data. The EGM96 spherical harmonic model was
in all cases used in a remove–restore mode. A total of 198 gravity disturbances spaced approximately 3 km apart were used,
as well as 35 GPS/levelling points in the vicinity and on the Aswan Dam. No data on the Nasser Lake were available. This gave
difficulties when using FFT, which requires the use of gridded data. When using exclusively the gravity disturbances, the
agreement between the GPS/levelling data were 0.71 ± 0.17 m for FFT and 0.63 ± 0.15 for LSC. When combining gravity disturbances
and GPS/levelling, the LSC error estimate was ±0.10 m. In the latter case two bias parameters had to be introduced to account
for a possible levelling datum difference between the levelling on the dam and that on the adjacent roads.
Received: 14 August 2000 / Accepted: 28 February 2001 相似文献
2.
Many regions around the world require improved gravimetric data bases to support very accurate geoid modeling for the modernization
of height systems using GPS. We present a simple yet effective method to assess gravity data requirements, particularly the
necessary resolution, for a desired precision in geoid computation. The approach is based on simulating high-resolution gravimetry
using a topography-correlated model that is adjusted to be consistent with an existing network of gravity data. Analysis of
these adjusted, simulated data through Stokes’s integral indicates where existing gravity data must be supplemented by new
surveys in order to achieve an acceptable level of omission error in the geoid undulation. The simulated model can equally
be used to analyze commission error, as well as model error and data inconsistencies to a limited extent. The proposed method
is applied to South Korea and shows clearly where existing gravity data are too scarce for precise geoid computation. 相似文献
3.
J. F. Kirby 《Journal of Geodesy》2003,77(7-8):433-439
The geoid gradient over the Darling Fault in Western Australia is extremely high, rising by as much as 38 cm over only 2 km. This poses problems for gravimetric-only geoid models of the area, whose frequency content is limited by the spatial distribution of the gravity data. The gravimetric-only version of AUSGeoid98, for instance, is only able to resolve 46% of the gradient across the fault. Hence, the ability of GPS surveys to obtain accurate orthometric heights is reduced. It is described how further gravity data were collected over the Darling Fault, augmenting the existing gravity observations at key locations so as to obtain a more representative geoid gradient. As many of the gravity observations were collected at stations with a well-known GRS80 ellipsoidal height, the opportunity arose to compute a geoid model via both the Stokes and the Hotine approaches. A scheme was devised to convert free-air anomaly data to gravity disturbances using existing geoid models, followed by a Hotine integration to geoid heights. Interestingly, these results depended very weakly upon the choice of input geoid model. The extra gravity data did indeed improve the fit of the computed geoid to local GPS/Australian Height Datum (AHD) observations by 58% over the gravimetric-only AUSGeoid98. While the conventional Stokesian approach to geoid determination proved to be slightly better than the Hotine method, the latter still improved upon the gravimetric-only AUSGeoid98 solution, supporting the viability of conducting gravity surveys with GPS control for the purposes of geoid determination.
AcknowledgementsThe author would like to thank Will Featherstone, Ron Gower, Ron Hackney, Linda Morgan, Geoscience Australia, Scripps Oceanographic Institute and the three anonymous reviewers of this paper. This research was funded by the Australian Research Council. 相似文献
4.
基于重力场水平分量-垂线偏差对地形信息敏感的特点,根据边值理论由重力与地形数据确定格网垂线偏差模型,在此基础上,首先利用三维重力矢量-格网垂线偏差与格网重力异常,联合格网高程数据求得格网点间高程异常差,然后通过GPS/水准点的控制,构成紧密的几何条件,进行严密平差,从而获得高分辨率、高精度似大地水准面的数值模型。按照本文方法,利用我国6600多个GPS/水准点、1'×1'的格网垂线偏差、格网重力异常、格网高程数据,整体平差计算了我国陆海统一的似大地水准面模型,经GPS/水准点检核,全国似大地水准面的绝对精度达到了4 cm,相对精度优于7 cm。 相似文献
5.
为解决CORS系统中GNSS高程受技术条件限制精度不高的问题,贵阳市进行了区域似大地水准面精化工作。本文论述了GNSS和水准网的布设及精度,使用了3 877个点重力数据和54个GNSS水准资料,以EIGEN03C地球重力场模型作为参考重力场,由第二类Helmert凝集法完成大地水准面计算,利用球冠谐调和分析方法将GNSS水准与重力似大地水准面联合求解得出的2'!2'格网似大地水准面,在高原高差地区其精度达到"0.010 m。 相似文献
6.
7.
R. Kiamehr 《Journal of Geodesy》2006,79(10-11):602-612
The computation of regional gravimetric geoid models with reasonable accuracy, in developing countries, with sparse data is a difficult task that needs great care. Here we investigate the procedure for gathering, evaluating and combining different data for the determination of a gravimetric geoid model for Iran, where limited ground gravity data are available. Heterogeneous data, including gravity anomalies, the high-resolution Shuttle Radar Topography Mission global digital terrain model and different global geopotential models including recently published Gravity Recovery and Climate Experiment models, are combined through least-squares modification of the Stokes formula. The new gravimetric geoid model, IRG04, agrees considerably better with GPS/levelling than any of the other recent local geoid model in the area. Its RMS fit with GPS/levelling is 0.27 m and 3.8 ppm in the absolute and relative view, respectively. The relative accuracy of IRG04 is four times better than the most recently published global and regional geoid models available in this area. This progress shows the practical potential of the method of least-squares modification of Stokes’s formula in combination with heterogeneous data for regional geoid determination 相似文献
8.
The long-wavelength geoid errors on large-scale geoid solutions, and the use of modified kernels to mitigate these effects,
are studied. The geoid around the Nordic area, from Greenland to the Ural mountains, is considered. The effect of including
additional gravity data around the Nordic/Baltic land area, originating from both marine, satellite and ground-based measurements,
is studied. It is found that additional data appear to increase the noise level in computations, indicating the presence of
systematic errors. Therefore, the Wong–Gore modification to the Stokes kernel is applied. This method of removing lower-order
terms in the Stokes kernel appears to improve the geoid. The best fit to the global positioning system (GPS) leveling points
is obtained with a degree of modification of approximately 30. In addition to the study of modification errors, the results
of different methods of combining satellite altimetry gravity and other gravimetry are presented. They all gave comparable
results, at the 6-cm level, when evaluated for the Nordic GPS networks. One dimensional (1-D) and 2-D fast Fourier transform
(FFT) methods are also compared. It is shown that even though methods differ by up to 6 cm, the fit to the GPS is essentially
the same. A surprising conclusion is that the addition of more data does not always produce a better geoid, illustrating the
danger of systematic errors in data.
Received: 4 July 2001 / Accepted: 21 February 2002 相似文献
9.
给定内插高程异常值的精度时对GPS水准网格间距的考虑 总被引：7，自引：0，他引：7
在已布设GPS水准网的地区，若需内插其中任意一点的高程异常值时，应该了解该内插值的精度。导出了该内插点高程异常值的精度评定方法，并具体给出在我国C级GPS水准网中，该内插点高程异常推估值精度和该地区的地形和栅格重力异常分辨率的数学关系式和实例。在给定内插点高程异常值精度的局域大地水准面时，按不同地形和栅格重力异常分辨率的密度，根据这些数学关系式，可以设计间距合理的B级或C级GPS水准网。 相似文献
10.
利用了双输入单输出法，融合处理了我国某地区的重力异常和地形资料两类数据，结合WDM94地球重力场模型和63个高精度GPS水准数据，计算了该区域的似大地水准面。 相似文献
11.
简述了GPS高程拟合的原理,采用移去一恢复法,结合最新的高精度地球重力场模型EGM2008,运用地统计学中的泛克里格方法（Kriging）,充分考虑先验统计信息以及各点的空间相关性,在无偏性和最小方差原则下,准确获取了未知点的高程异常。经实例验证：该方法具有模型严密、可靠性好、拟合精度高等优点,适用于地形复杂地区。 相似文献
12.
Summary A new basic geodetic network using the GPS technique is now being set up in France. There will be altogether 1000 benchmarks connected to the French levelling network. Obviously, the GPS levelling points are not dense enough to produce a national levelling reference surface. A gravimetrically determined geoid has therefore been proposed to be used for the interpolation between the GPS levelling points. However, because of long-wavelength errors, we consider that a gravimetric geoid does not have sufficient accuracy. A regression by fitting the gravimetrically determined geoid to the GPS levelling points is generally proposed. Unfortunately, this country-wide geoid fitting work cannot eliminate local deformations in the geoid, which happen in areas where there are errors or shortages of gravity or DTM data. This paper proposes and discusses a combined adjustment method. The principle is to divide up the geoid into small pieces and then to adjust them to the GPS levelling points locally with constraint conditions for the common points of the adjacent pieces. In order to benefit from the advantages of the high resolution and high relative accuracy of the gravimetric geoid, as well as the high absolute accuracy of the GPS levelling points, we establish respectively a relative observation equation for the difference of the gravimetric geoid undulation and an absolute observation equation for the GPS levelling points. Finally, we adjust the observation equations as a whole. Several global and local systematic errors are also taken into account and some special cases, such as adjustment in groups and blunder detection, are also discussed. 相似文献
13.
我国大地测量学的进展和展望 总被引：8，自引：1，他引：7
回顾了我国大地测量工作的进展。面向 2 1世纪前期的我国经济和国防建设及科技和社会发展 ,展望了我国新世纪的大地测量 ,提出应逐步进入精确、动态、实时的现代化体系 ,即完善国家三维空间大地网 ;建立 GPS综合服务体系 ;提供导航和定位服务 ;测定地壳运动、电离层参数、大气中可降水份等信息 ;精化中国地区重力场参数 ;建立新的国家重力基准网 ;完成分米级精度的中国似大地水准面的推算 ;积极开展海洋和空间大地测量 ,为资源、环境的管理以及防灾监测做出应有的贡献。 相似文献
14.
综合利用EGM2008地球重力场模型,采用＂移去-拟合-恢复＂方法和二次曲面函数数值逼近算法进行GPS高程转换。通过某隧道实例验证了＂移去-拟合-恢复＂的有效性和实用性,检验了EGM2008地球重力场模型的精度。通过计算比较,在测区范围内,合理选择均匀分布的GPS/水准点,可以使高程拟合精度达到最大。 相似文献
15.
Y. M. Wang C. Becker G. Mader D. Martin X. Li T. Jiang S. Breidenbach C. Geoghegan D. Winester S. Guillaume B. Bürki 《Journal of Geodesy》2017,91(10):1261-1276
Three Geoid Slope Validation Surveys were planned by the National Geodetic Survey for validating geoid improvement gained by incorporating airborne gravity data collected by the “Gravity for the Redefinition of the American Vertical Datum” (GRAV-D) project in flat, medium and rough topographic areas, respectively. The first survey GSVS11 over a flat topographic area in Texas confirmed that a 1-cm differential accuracy geoid over baseline lengths between 0.4 and 320 km is achievable with GRAV-D data included (Smith et al. in J Geod 87:885–907, 2013). The second survey, Geoid Slope Validation Survey 2014 (GSVS14) took place in Iowa in an area with moderate topography but significant gravity variation. Two sets of geoidal heights were computed from GPS/leveling data and observed astrogeodetic deflections of the vertical at 204 GSVS14 official marks. They agree with each other at a \({\pm }1.2\,\, \hbox {cm}\) level, which attests to the high quality of the GSVS14 data. In total, four geoid models were computed. Three models combined the GOCO03/5S satellite gravity model with terrestrial and GRAV-D gravity with different strategies. The fourth model, called xGEOID15A, had no airborne gravity data and served as the benchmark to quantify the contribution of GRAV-D to the geoid improvement. The comparisons show that each model agrees with the GPS/leveling geoid height by 1.5 cm in mark-by-mark comparisons. In differential comparisons, all geoid models have a predicted accuracy of 1–2 cm at baseline lengths from 1.6 to 247 km. The contribution of GRAV-D is not apparent due to a 9-cm slope in the western 50-km section of the traverse for all gravimetric geoid models, and it was determined that the slopes have been caused by a 5 mGal bias in the terrestrial gravity data. If that western 50-km section of the testing line is excluded in the comparisons, then the improvement with GRAV-D is clearly evident. In that case, 1-cm differential accuracy on baselines of any length is achieved with the GRAV-D-enhanced geoid models and exhibits a clear improvement over the geoid models without GRAV-D data. GSVS14 confirmed that the geoid differential accuracies are in the 1–2 cm range at various baseline lengths. The accuracy increases to 1 cm with GRAV-D gravity when the west 50 km line is not included. The data collected by the surveys have high accuracy and have the potential to be used for validation of other geodetic techniques, e.g., the chronometric leveling. To reach the 1-cm height differences of the GSVS data, a clock with frequency accuracy of \(10^{-18}\) is required. Using the GSVS data, the accuracy of ellipsoidal height differences can also be estimated. 相似文献
16.
顾及非格网数据考虑地形改正的GPS水准高程拟合 总被引：2，自引：0，他引：2
系统地分析了目前常用的确定高程异常的重力法和几何法在山区GPS网中的局限性。提出了一种顾及非格网数据考虑地形改正的GPS水准高程拟合法,同时对利用非格网数据和内插格网概略大地高所造成的影响也进行了估计。建议在地形起伏较大地区,借助地形图内插部分特征点作为虚拟GPS观测值,参与整体内插计算,有助于提高计算精度。 相似文献
17.
18.
Ahmed Elaksher Tarig Ali Franck Kamtchang Christian Wegmann Adalberto Guerrero 《International Journal of Digital Earth》2020,13(5):586-601
ABSTRACTEstablishing reliable elevation differences is imperative for most geoscience and engineering applications. This work has traditionally been accomplished through spirit leveling techniques; however, surveyors have been utilizing satellite positioning systems in measuring height differences for more than a decade. Yet the quality of these heights needs to be evaluated in order to adopt them in different applications. In this article, we present the outcome of an accuracy assessment of height differences obtained with static and RTK surveys. Twenty control points with an average baseline length of 1?km were occupied with dual-frequency GNSS receivers for different time periods. Collected signals were processed using open-source software and verified with an online processing tool. Heights were estimated by processing the GPS and the GLONASS data individually, and combined (i.e. GNSS). Height differences were determined and compared with those measured by spirit levels and corrected through geoid models. Best results were achieved by combining GPS and GLONASS solutions for both static and RTK surveys. Solutions with either GPS or GLONASS satellites were comparable, but in most cases, the GPS solutions performed better. For the static surveys, longer occupation provided much accurate height differences. Inconsistencies among 10 different RTK surveys were minimum for the GPS?+?GLONASS solutions and worst for the GLONASS solutions. The ANOVA, LSD, F, and χ² statistical tests confirmed our findings at the 95% confidence level. 相似文献
19.
Tim L. Webster 《国际地球制图》2013,28(4):11-19
Abstract In the summer of 2000, the Annapolis Valley of Nova Scotia, Canada was selected for a high‐resolution elevation survey utilizing LIDAR (Light Detection And Ranging). Two different LIDAR systems were used to acquire data for the area. The vertical accuracy specification for the survey called for heights to be within an average of 15 cm of measured GPS heights and 95% of the data to be within 30 cm. Prior to the application of these data to geoscientific problems, extensive validation procedures were employed. High precision GPS and traditional surveys were conducted to collect height validation checkpoints. Two validation methods were developed in a GIS environment that involved comparing the checkpoints to the original LIDAR points and to an interpolated “bald earth” DEM. A systematic height error between flight lines for one of the LIDAR methods was detected that related to the calibration procedures used in the survey. This study highlights the differences between laser systems, calibration and deployment methodologies and emphasizes the necessity for independent validation data. 相似文献
20.
Any errors in digital elevation models (DEMs) will introduce errors directly in gravity anomalies and geoid models when used
in interpolating Bouguer gravity anomalies. Errors are also propagated into the geoid model by the topographic and downward
continuation (DWC) corrections in the application of Stokes’s formula. The effects of these errors are assessed by the evaluation
of the absolute accuracy of nine independent DEMs for the Iran region. It is shown that the improvement in using the high-resolution
Shuttle Radar Topography Mission (SRTM) data versus previously available DEMs in gridding of gravity anomalies, terrain corrections
and DWC effects for the geoid model are significant. Based on the Iranian GPS/levelling network data, we estimate the absolute
vertical accuracy of the SRTM in Iran to be 6.5 m, which is much better than the estimated global accuracy of the SRTM (say
16 m). Hence, this DEM has a comparable accuracy to a current photogrammetric high-resolution DEM of Iran under development.
We also found very large differences between the GLOBE and SRTM models on the range of −750 to 550 m. This difference causes
an error in the range of −160 to 140 mGal in interpolating surface gravity anomalies and −60 to 60 mGal in simple Bouguer
anomaly correction terms. In the view of geoid heights, we found large differences between the use of GLOBE and SRTM DEMs,
in the range of −1.1 to 1 m for the study area. The terrain correction of the geoid model at selected GPS/levelling points
only differs by 3 cm for these two DEMs. 相似文献