共查询到20条相似文献，搜索用时 617 毫秒
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.
The determination of potential difference by the joint application of measured and synthetical gravity data: a case study in Hungary 总被引：1，自引：1，他引：0
In an elementary approach every geometrical height difference between the staff points of a levelling line should have a corresponding
average g value for the determination of potential difference in the Earth’s gravity field. In practice this condition requires as
many gravity data as the number of staff points if linear variation of g is assumed between them. Because of the expensive fieldwork, the necessary data should be supplied from different sources.
This study proposes an alternative solution, which is proved at a test bed located in the Mecsek Mountains, Southwest Hungary,
where a detailed gravity survey, as dense as the staff point density (~1 point/34 m), is available along a 4.3-km-long levelling
line. In the first part of the paper the effect of point density of gravity data on the accuracy of potential difference is
investigated. The average g value is simply derived from two neighbouring g measurements along the levelling line, which are incrementally decimated in the consecutive turns of processing. The results
show that the error of the potential difference between the endpoints of the line exceeds 0.1 mm in terms of length unit if
the sampling distance is greater than 2 km. Thereafter, a suitable method for the densification of the decimated g measurements is provided. It is based on forward gravity modelling utilising a high-resolution digital terrain model, the
normal gravity and the complete Bouguer anomalies. The test shows that the error is only in the order of 10−3mm even if the sampling distance of g measurements is 4 km. As a component of the error sources of levelling, the ambiguity of the levelled height difference which
is the Euclidean distance between the inclined equipotential surfaces is also investigated. Although its effect accumulated
along the test line is almost zero, it reaches 0.15 mm in a 1-km-long intermediate section of the line. 相似文献
3.
Heiner Denker Ludger Timmen Christian Voigt Stefan Weyers Ekkehard Peik Helen S. Margolis Pacôme Delva Peter Wolf Gérard Petit 《Journal of Geodesy》2018,92(5):487-516
The frequency stability and uncertainty of the latest generation of optical atomic clocks is now approaching the one part in \(10^{18}\) level. Comparisons between earthbound clocks at rest must account for the relativistic redshift of the clock frequencies, which is proportional to the corresponding gravity (gravitational plus centrifugal) potential difference. For contributions to international timescales, the relativistic redshift correction must be computed with respect to a conventional zero potential value in order to be consistent with the definition of Terrestrial Time. To benefit fully from the uncertainty of the optical clocks, the gravity potential must be determined with an accuracy of about \(0.1\,\hbox {m}^{2}\,\hbox {s}^{-2}\), equivalent to about 0.01 m in height. This contribution focuses on the static part of the gravity field, assuming that temporal variations are accounted for separately by appropriate reductions. Two geodetic approaches are investigated for the derivation of gravity potential values: geometric levelling and the Global Navigation Satellite Systems (GNSS)/geoid approach. Geometric levelling gives potential differences with millimetre uncertainty over shorter distances (several kilometres), but is susceptible to systematic errors at the decimetre level over large distances. The GNSS/geoid approach gives absolute gravity potential values, but with an uncertainty corresponding to about 2 cm in height. For large distances, the GNSS/geoid approach should therefore be better than geometric levelling. This is demonstrated by the results from practical investigations related to three clock sites in Germany and one in France. The estimated uncertainty for the relativistic redshift correction at each site is about \(2 \times 10^{-18}\). 相似文献
4.
5.
基于德国地学中心（GFZ）发布的GRACE RL05月重力场模型数据,考虑全球陆地同化系统陆地水储量的影响,采用300 km的扇形滤波,利用叠积法提取了日本Mw9.0地震的同震和震后重力时变信号,并利用最小二乘拟合的方法计算了两个同震重力变化极值点在地震前后85个月的重力年变率。结果表明：土壤水分和雪水引起的重力变化为-0.34~0.09 μgal;利用GRACE数据检测到的同震重力变化为-5.3~4.2 μgal,与基于PSGRN/PSCMP模型计算的结果在空间分布和量级上具有较好的一致性;震后5 a震中附近区域的重力整体上呈现增加趋势,断层上盘所在的日本海域与下盘所在的太平洋区域重力增加的最大值分别为2.6、4.5 μgal,下盘重力增加较大,可能与断层下盘所在地层的黏滞性相对较低有关。 相似文献
6.
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
7.
Combining EGM2008 and SRTM/DTM2006.0 residual terrain model data to improve quasigeoid computations in mountainous areas devoid of gravity data 总被引：6，自引：4，他引：2
A global geopotential model, like EGM2008, is not capable of representing the high-frequency components of Earth’s gravity
field. This is known as the omission error. In mountainous terrain, omission errors in EGM2008, even when expanded to degree
2,190, may reach amplitudes of 10 cm and more for height anomalies. The present paper proposes the utilisation of high-resolution
residual terrain model (RTM) data for computing estimates of the omission error in rugged terrain. RTM elevations may be constructed
as the difference between the SRTM (Shuttle Radar Topography Mission) elevation model and the DTM2006.0 spherical harmonic
topographic expansion. Numerical tests, carried out in the German Alps with a precise gravimetric quasigeoid model (GCG05)
and GPS/levelling data as references, demonstrate that RTM-based omission error estimates improve EGM2008 height anomaly differences
by 10 cm in many cases. The comparisons of EGM2008-only height anomalies and the GCG05 model showed 3.7 cm standard deviation
after a bias-fit. Applying RTM omission error estimates to EGM2008 reduces the standard deviation to 1.9 cm which equates
to a significant improvement rate of 47%. Using GPS/levelling data strongly corroborates these findings with an improvement
rate of 49%. The proposed RTM approach may be of practical value to improve quasigeoid determination in mountainous areas
without sufficient regional gravity data coverage, e.g., in parts of Asia, South America or Africa. As a further application,
RTM omission error estimates will allow refined validation of global gravity field models like EGM2008 from GPS/levelling
data. 相似文献
8.
Astronomical-topographic levelling using high-precision astrogeodetic vertical deflections and digital terrain model data 总被引：2，自引：1，他引：1
At the beginning of the twenty-first century, a technological change took place in geodetic astronomy by the development of
Digital Zenith Camera Systems (DZCS). Such instruments provide vertical deflection data at an angular accuracy level of 0.̋1
and better. Recently, DZCS have been employed for the collection of dense sets of astrogeodetic vertical deflection data in
several test areas in Germany with high-resolution digital terrain model (DTM) data (10–50 m resolution) available. These
considerable advancements motivate a new analysis of the method of astronomical-topographic levelling, which uses DTM data
for the interpolation between the astrogeodetic stations. We present and analyse a least-squares collocation technique that
uses DTM data for the accurate interpolation of vertical deflection data. The combination of both data sets allows a precise
determination of the gravity field along profiles, even in regions with a rugged topography. The accuracy of the method is
studied with particular attention on the density of astrogeodetic stations. The error propagation rule of astronomical levelling
is empirically derived. It accounts for the signal omission that increases with the station spacing. In a test area located
in the German Alps, the method was successfully applied to the determination of a quasigeoid profile of 23 km length. For
a station spacing from a few 100 m to about 2 km, the accuracy of the quasigeoid was found to be about 1–2 mm, which corresponds
to a relative accuracy of about 0.05−0.1 ppm. Application examples are given, such as the local and regional validation of
gravity field models computed from gravimetric data and the economic gravity field determination in geodetically less covered
regions. 相似文献
9.
Spherical harmonic expansions of the geopotential are frequently used for modelling the earth’s gravity field. Degree and
order of recently available models go up to 360, corresponding to a resolution of about50 km. Thus, the high degree potential coefficients can be verified nowadays even by locally distributed sets of terrestrial gravity
anomalies. These verifications are important when combining the short wavelength model impact, e.g. for regional geoid determinations
by means of collocation solutions. A method based on integral formulae is presented, enabling the improvement of geopotential
models with respect to non-global distributed gravity anomalies. To illustrate the foregoing, geoid computations are carried
out for the area of Iran, introducing theGPM2 geopotential model in combination with available regional gravity data. The accuracy of the geoid determination is estimated
from a comparison with Doppler and levelling data to ±1.4m. 相似文献
10.
Junyong Chen 《Journal of Geodesy》1996,70(11):798-804
The strategy for the determination of a new local geoid in China is: (1) This task should be fulfilled in a short time as possible; (2) The new local geoid can be with different resolution and accuracy, which depend on the needs of the social and economical development in different regions; (3) The newly established height anomaly control network, i.e. a gridded GPS levelling network should combine as possible with the existing astro-gravimetric levelling network; (4) Global geopotential model, DTM and surface gravity data are used to densify the resolution of the local geoid with remove-restore technique. The accuracy and resolution possibly obtained nowadays within the capability of China are discussed. The required accuracies for GPS positioning, levelling and coordinate transformation are suggested. 相似文献
11.
Fast and accurate relative positioning for baselines less than 20 km in length is possible using dual-frequency Global Positioning
System (GPS) receivers. By measuring orthometric heights of a few GPS stations by differential levelling techniques, the geoid
undulation can be modelled, which enables GPS to be used for orthometric height determination in a much faster and more economical
way than terrestrial methods. The geoid undulation anomaly can be very useful for studying tectonic structure. GPS, levelling
and gravity measurements were carried out along a 200-km-long highly undulating profile, at an average elevation of 4000 m,
in the Ladak region of NW Himalaya, India. The geoid undulation and gravity anomaly were measured at 28 common GPS-levelling
and 67 GPS-gravity stations. A regional geoid low of nearly −4 m coincident with a steep negative gravity gradient is compatible
with very recent findings from other geophysical studies of a low-velocity layer 20–30 km thick to the north of the India–Tibet
plate boundary, within the Tibetan plate. Topographic, gravity and geoid data possibly indicate that the actual plate boundary
is situated further north of what is geologically known as the Indus Tsangpo Suture Zone, the traditionally supposed location
of the plate boundary. Comparison of the measured geoid with that computed from OSU91 and EGM96 gravity models indicates that
GPS alone can be used for orthometric height determination over the Higher Himalaya with 1–2 m accuracy.
Received: 10 April 1997 / Accepted: 9 October 1998 相似文献
12.
Elke Stöcker-Meier 《Journal of Geodesy》1990,64(3):247-258
The problem of improving the geoid from satellite altimetry is formulated and studied within the scope of geophysical fluid
dynamics. The oceanic levelling is defined by analogy to the astrogeodetic levelling and it is used to determine the sea surface
topography as a function of current velocity, atmospheric pressure and viscosity. Simulating strong currents like the Gulf
Stream or the Kuroshio the numerical treatment of the oceanic levelling shows that the sea surface topography can come up
to an order of magnitude of1–2 m, whereby the results depend on latitude and slightly on the actual pressure conditions. 相似文献
13.
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
14.
15.
应用GRACE卫星数据反演高精度静态地球重力场是大地测量学界的热点之一。考虑到经典动力学法线性化误差随弧长拉长而迅速增长,本文以GRACE卫星轨道观测值为初值的线性化方法,建立了应用GRACE卫星轨道和星间距离变率反演地球重力场的改进动力学法理论模型。利用2003年1月至2010年12月的GRACE卫星姿态、轨道、星间距离变率和非保守力加速度等观测数据,解算了一个180阶次的无约束全球静态重力场模型Tongji-Dyn01s和一个采用Kaula规则约束的全球重力场模型Tongji-Dyn01k。与国际不同机构最新发布的纯GRACE数据解算的重力场模型(包括AIUB-GRACE03S、GGM05S、ITSG-Grace2014k和Tongji-GRACE01)进行比较,并利用DTU13海洋重力异常和GPS/水准高程异常进行外部检核,结果表明,Tongji-Dyn01s与国际最新模型精度处于同一水平,然而Tongji-Dyn01k模型总体上更加靠近EIGEN6C2重力场模型。 相似文献
16.
2022年1月15日汤加火山剧烈喷发产生了波及全球的大气重力波,距离火山8 736~12 758 km的中国大陆所有地应变观测站清晰记录到由此产生的短时地表应变变化。应用小波分析方法系统分析了中国近200个地应变观测站记录数据的时空响应与频率特征,主要表现为:由大气重力波激发的短时地表应变变化的持续时间约为1.5 h,其中能量最强的变化集中在前40 min,面应变平均变幅约为186×10-10,呈现出单脉冲起伏状变化,形态具有很强的一致性,具备兰姆波传播属性;短时地表应变变化的平均传播速度约为310 m/s,与大气重力波传播速度基本一致。部分观测站还记录到绕地球一圈后再次到达的大气重力波对地表的作用。这是首次通过大范围布设的高精度地应变观测仪记录到大气重力波作用于地表的痕迹,有助于认识地壳运动和大气圈层相互影响的机制。 相似文献
17.
本文以有限单元法为基础，将四维整体大地测量模型与固体力学方程求解构造应力场结合起来，在四维整体大地测量方程中加入了由地壳构造运动产生的地面点重力变化的观测方程，其中包含测点的位移参数，边界结点上待求以数利用有限单元法在四维整体大地测量平差过程中推估，采用统一的插值函数。 相似文献
18.
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
19.
N. J. Brown J. C. McCubbine W. E. Featherstone N. Gowans A. Woods I. Baran 《Journal of Geodesy》2018,92(12):1457-1465
AUSGeoid2020 is a combined gravimetric–geometric model (sometimes called a “hybrid quasigeoid model”) that provides the separation between the Geocentric Datum of Australia 2020 (GDA2020) ellipsoid and Australia’s national vertical datum, the Australian Height Datum (AHD). This model is also provided with a location-specific uncertainty propagated from a combination of the levelling, GPS ellipsoidal height and gravimetric quasigeoid data errors via least squares prediction. We present a method for computing the relative uncertainty (i.e. uncertainty of the height between any two points) between AUSGeoid2020-derived AHD heights based on the principle of correlated errors cancelling when used over baselines. Results demonstrate AUSGeoid2020 is more accurate than traditional third-order levelling in Australia at distances beyond 3 km, which is 12 mm of allowable misclosure per square root km of levelling. As part of the above work, we identified an error in the gravimetric quasigeoid in Port Phillip Bay (near Melbourne in SE Australia) coming from altimeter-derived gravity anomalies. This error was patched using alternative altimetry data. 相似文献
20.
本文根据局部重力场逼近的虚拟质点方法,导出整体大地测量的虚拟点质量模型,给出了地面大地测量及GPS水准观测在这一模型下的观测方程,并讨论了有关问题。 相似文献