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1.
Unification of New Zealand’s local vertical datums: iterative gravimetric quasigeoid computations 总被引：2，自引：2，他引：0
New Zealand uses 13 separate local vertical datums (LVDs) based on geodetic levelling from 12 different tide-gauges. We describe
their unification using a regional gravimetric quasigeoid model and GPS-levelling data on each LVD. A novel application of
iterative quasigeoid computation is used, where the LVD offsets computed from earlier models are used to apply additional
gravity reductions from each LVD to that model. The solution converges after only three iterations yielding LVD offsets ranging
from 0.24 to 0.58 m with an average standard deviation of ±0.08 m. The so-computed LVD offsets agree, within expected data
errors, with geodetically levelled height differences at common benchmarks between adjacent LVDs. This shows that iterated
quasigeoid models have a role in vertical datum unification. 相似文献
2.
永久性潮汐与大地测量基准 总被引：10，自引：2，他引：8
社会、经济和科技的发展,对大地测量基准的精度、历元、框架等方面的要求愈来愈高,因此必须顾及具有同等精度量级的地球动力现象如潮汐、极移、地壳运动、冰后期反弹等对大地测量基准的影响。本文仅讨论永久性潮汐对重力基准、高程基准、大地水准面、垂线偏差等方面的影响。对大地测量基准中使用的无潮汐、平均湖汐和零潮汐等概念和相关计算进行了推导和讨论。 相似文献
3.
为实现远岸潮汐精确监测及潮位海图高程转换,基于GPS事后动态处理技术(PPK)开展了远距离高精度潮位观测、提取及垂直基准面确定和转换模型构建方法研究。分别探讨了在锚定和走航情况下瞬时水面高程信号改正方法及潮位有效信息提取的最优截止频率,并给出了在不同情况下深度基准面大地高的计算方法模型及区域无缝深度基准面大地高构建模型。在实际试验中,基线距离在100km范围内,获得了基于深度基准的GPS潮位,精度优于10cm。 相似文献
4.
全球高程基准统一是继全球大地测量坐标系及其参考基准统一之后,大地测量学科面临和亟待解决的一个重要问题,也是全球空间信息共享与交换的基础。本文针对区域高程基准与全球高程基准间基准差异确定的理论、方法及实际问题开展研究。利用物理大地测量高程系统的经典理论方法,给出了高程基准差异的定义,并推导了计算基准差异的严密公式,该公式可将高程基准差异确定的现有3种方法统一起来。在此基础上,分析顾及了不同椭球参数对于计算基准差异的影响及量级,同时,高程异常差法还需考虑全球高程基准重力位与模型计算大地水准面位值不一致引起的零阶项改正。利用青岛原点附近152个GPS水准点数据,分别选择GRS80、WGS-84、CGCS2000参考椭球以及EGM2008、EIGEN-6C4、SGG-UGM-1模型,采用位差法和高程异常差法,确定了我国1985高程基准与全球高程基准的差异。其中,EIGEN-6C4模型计算的我国高程基准与WGS-84参考椭球正常重力位U0定义的全球高程基准之间的差异约为-23.1cm。也就是说,我国高程基准低于采用WGS-84参考椭球正常重力位U0定义的全球高程基准,当选取基于平均海面确定的Gauss-Listing大地水准面作为全球高程基准时,我国1985高程基准高于全球基准约21.0cm。从计算结果还可看出,当前重力场模型在青岛周边不同GPS/水准点的精度差别依然较大,这会导致选择不同数据对确定我国85国家高程基准与全球基准之间的差异影响较大,因此,若要实现厘米级精度区域高程基准与全球高程基准的统一,全球重力场模型的精度和可靠性还需要进一步提高。 相似文献
5.
International compilations of marine gravity, such as the International Gravity Bureau (BGI) contain tens of millions of point
data. Lemoine et al. (The Development of the Joint NASA GSFC and the National Imagery and Mapping Agency (NIMA) Geopotential
Model EGM96, NASA/TP-1998-206861) chose not to include any marine gravity in the construction of the global gravity model
EGM96. Instead they used synthetic anomalies derived from altimetry, so that no independent information about Mean Dynamic
Topography (MDT) can be deduced. Software has been developed not only to identify and correct those aspects of marine gravity
data that are unreliable, but to do so in a way that can be applied to very large, ocean-wide data sets. First, we select
only straight-line parts of ship-tracks and fit each one with a high-degree series of Chebyshev polynomials, whose misfit
standard deviation is σ
line and measures the random error associated with point gravity data. Then, network adjustment determines how the gravity datum is offset for each survey.
A free least squares adjustment minimises the gravity anomaly mismatch at line-crossing points, using σ
line to weight the estimate for each line. For a long, well crossed survey, the instrumental drift rate is also adjusted. For
some 42,000 cross-over points in the northern Atlantic Ocean, network adjustment reduces the unweighted standard deviation
of the cross-over errors from 4.03 to 1.58 mGal; when quality weighted, the statistic reduces from 1.32 to 0.39 mGal. The
geodetic MDT is calculated combining the adjusted gravity anomalies and satellite altimetry, and a priori global ocean model
through a new algorithm called the Iterative Combination Method. This paper reports a first demonstration that geodetic oceanography
can characterise the details of basin wide ocean circulation with a resolution better than global ocean circulation models.
The result matches regional models of ocean circulation from hydrography measurements (Geophys Res Lett 29:1896, 2002; J Geophys
Res 108:3251, 2003). 相似文献
6.
Height datum definition,height datum connection and the role of the geodetic boundary value problem 总被引：3，自引：3，他引：3
Vertical datum definition is identical with the choice of a potential (or height) value for the fundamental bench mark. Also
the connection of two adjacent vertical datums poses no principal problem as long as the potential (or height) value of two
bench marks of the two systems is known and they can be connected by levelling. Only the unification of large vertical datums
and the connection of vertical datums separated by an ocean remains difficult.
Two vertical datums can be connected indirectly by means of a combination of precise geocentric positions of two points, as
derived by space techniques, their potential (or height) value in the respective height datum and their geoid height difference.
The latter requires the solution of the linear geodetic boundary value problem under the assumption that potential and gravity
anomalies refer to a variety of height datums. The unknown off-sets between the various datums appear in the solution inside
and outside the Stokes integral and can be estimated in a least squares adjustment, if geocentric positions, levelled heights
and adequate gravity material are available for all datum zones. The problem can in principle also be solved involving only
two datums, in case a precise global gravity field becomes available purely from satellite methods. 相似文献
7.
长江口水域地形地貌研究对河道治理建设、水上交通运输等人类社会经济活动具有重要意义,而建立高精度的无缝深度基准面及其与其他垂直基准间转换模型将直接影响到水陆交界区高精度地形地貌数据的获取及统一综合管理与分析。为此着重研究了基于三维潮波运动数值模拟、海面地形和大地水准面3种手段联合的河口水域无缝深度基准面构建及其与其他垂直基准间转换模型,并在长江口南支这一典型河口水域进行了建模实验和模型精度评估分析。结果显示,垂直基准转换模型中误差为12.4 cm,与现场长期潮位站实际观测结果比对分析得垂直基准转换模型误差绝对值均值为24.2 cm,尽管大于模型中误差估值,但仍满足国际水道测量规范对测深中垂向最大不确定度的要求。 相似文献
8.
为解决世界各国高程基准差异的问题,提出联合卫星重力场模型、地面重力数据、GNSS大地高、局部高程基准的正高或正常高,按大地边值问题法确定局部高程基准重力位差的方法。首先推导了利用传统地面"有偏"重力异常确定高程基准重力位差的方法;接着利用改化Stokes核函数削弱"有偏"重力异常的影响,并联合卫星重力场模型和地面"有偏"重力数据,得到独立于任何局部高程基准的重力水准面,以此来确定局部高程基准重力位差;最后利用GNSS+水准数据和重力大地水准面确定了美国高程基准与全球高程基准W0的重力位差为-4.82±0.05 m2s-2。 相似文献
9.
受特殊海岸线及复杂海底地形的影响,目前发布的全球海潮模型在局部沿海地区差异较大,需利用其他大地测量手段直接测定沿海地区的海潮负荷位移参数。GPS技术因具有全天候、精度高、成本低等优势,已成为获取海潮负荷位移参数的有效手段。本文基于GPS技术监测测站三维位移变化的灵敏度高于监测48个海潮参数的灵敏度这一基本思想,改进了利用GPS精密单点定位(PPP)技术估计48个海潮调和参数的方法,直接逐历元求解三维海潮负荷位移变化,再利用调和分析方法提取主要潮波(M2、S2、N2、K2、K1、O1、P1、Q1)的海潮负荷位移建模参数(振幅与相位)。利用12个香港连续运行参考站(CORS)8年的GPS观测数据,计算各测站的海潮负荷位移建模参数。与传统方法比较,本文方法可有效加速K1潮波在东西方向的收敛。将GPS海潮负荷位移建模参数估值与中国近海海潮模型值比较,发现除S2、K2和K1潮波的均方根误差较大外,其他潮波的均方根误差均小于1.5mm。将香港2008—2014年验潮站数据反演的潮波参数与海潮模型值比较,结果表明:GPS与验潮站数据反演的潮波参数均与中国近海海潮模型及HAMTIDE2011.11A全球海潮模型符合较好,验证了GPS PPP反演海潮负荷位移的有效性。采用GPS PPP估计的8个潮波的振幅与相位值替换全球海潮模型中对应的潮波值,进行海潮负荷效应改正,可减弱GPS长时间序列中的半周年信号。 相似文献
10.
GPS监测中国沿海验潮站垂直运动观测研究 总被引：2，自引：0，他引：2
利用2001年和2003年两期GPS观测数据,结合绝对重力测量结果分析了中国沿海海岸在欧亚框架下的水平运动及在全球框架ITRF2000下的垂直运动特征,并讨论了GPS定期观测与连续观测的区别。 相似文献
11.
GRACE、GOCE卫星重力计划的实施,对确定高精度重力场模型具有重要贡献。联合GRACE、GOCE卫星数据建立的重力场模型和我国均匀分布的649个GPS/水准数据可以确定我国高程基准重力位,但我国高程基准对应的参考面为似大地水准面,是非等位面,将似大地水准面转化为大地水准面后确定的大地水准面重力位为62 636 854.395 3m~2s~(-2),为提高高阶项对确定大地水准面的贡献,利用高分辨率重力场模型EGM2008扩展GRACE/GOCE模型至2190阶,同时将重力场模型和GPS/水准数据统一到同一参考框架和潮汐系统,最后利用扩展后的模型确定的我国大地水准面重力位为62 636 852.751 8m~2s~(-2)。其中组合模型TIM_R4+EGM2008确定的我国85高程基准重力位值62 636 852.704 5m~2s~(-2)精度最高。重力场模型截断误差对确定我国大地水准面的影响约16cm,潮汐系统影响约4~6cm。 相似文献
12.
Stavros A. Melachroinos Jean-Michel Lemoine Paul Tregoning Richard Biancale 《Journal of Geodesy》2009,83(10):915-923
Unmodeled sub-daily ocean S2 tide signals that alias into lower frequencies have been detected in the analysis of gravity recovery and climate experiment
(GRACE) space gravity fields of GRGS. The most significant global S2 aliased signal occurs off the northwest coast of Australia in a shallow continental shelf zone, a region with high tidal
amplitudes at a period of 161 days. The GRACE S2 aliased equivalent water height grids are convolved with Green’s functions to produce GRACE aliased tidal loading (GATL)
vertical displacements. The analysis of hourly global positioning system (GPS) vertical coordinate estimates at permanent
sites in the region confirms the presence of spectral power at the S2 frequency when the same ocean tide model (FES2004) was used. Thus, deficiencies in the FES2004 ocean tide model are detected
both directly and indirectly by the two independent space geodetic techniques. Through simulation, the admittance (ratio of
amplitude of spurious long-wavelength output signal in the GRACE time-series to amplitude of unmodeled periodic signals) of
the GRACE unmodeled S2 tidal signals, aliased to a 161-day period, is found to have a global average close to 100%, although with substantial spatial
variation. Comparing GATL with unmodeled S2 tidal sub-daily signals in the vertical GPS time-series in the region of Broome in NW Australia suggests an admittance of
110–130%. 相似文献
13.
R. Lehmann 《Journal of Geodesy》1999,73(9):491-500
A review of recent progress and current activities towards an improved formulation and solution of geodetic boundary value
problems is given. Improvements stimulated and required by the dramatic changes of the real world of geodetic measurements
are focused upon. Altimetry–gravimetry problems taking into account various scenarios of non-homogeneous data coverage are
discussed in detail. Other problems are related to free geodetic datum parameters, most of all the vertical datum, overdetermination
or additional constraints imposed by satellite geodetic observations or models. Some brief remarks are made on pseudo-boundary
value problems for geoid determination and on purely gravitational boundary-value problems.
Received: 17 March 1999 / Accepted: 19 April 1999 相似文献
14.
15.
We present a combined approach for the realization of the (quasi-)geoid as a height reference surface and the vertical reference surface at sea (chart datum). This approach, specifically designed for shallow seas and coastal waters, provides the relation between the two vertical reference surfaces without gaps down to the coast. It uses a regional hydrodynamic model, which, after vertical referencing, provides water levels relative to a given (quasi-)geoid. Conversely, the hydrodynamic model is also used to realize a (quasi-)geoid by providing corrections to the dynamic sea surface topography, which are used to reduce radar altimeter-derived sea surface heights to the (quasi-)geoid. The coupled problem of vertically referencing the hydrodynamic model and computing the (quasi-)geoid is solved iteratively. After convergence of the iteration process, the vertically referenced hydrodynamic model is used to realize the chart datum. In this way, consistency between the chart datum and (quasi-)geoid is ensured. We demonstrate the feasibility and performance of this approach for the Dutch mainland and North Sea. We show that in the Dutch part of the North Sea, the differences between modeled and observed instantaneous and mean dynamic sea surface topography is 8–10 and 5.8 cm, respectively. On land, we show that the methodology provides a quasi-geoid which has a lower standard deviation (SD) than the European Gravimetric Geoid 2008 (EGG08) and the official Netherlands quasi-geoid NLGEO2004-grav when compared to GPS-levelling data. The root mean square at 81 GPS-levelling points is below 1.4 cm; no correction surface is needed. Finally, we show that the chart datum (lowest astronomical tide, LAT) agrees with the observed chart datum at 92 onshore tide gauges to within 21.5 cm (SD). 相似文献
16.
T. Vincenty 《Journal of Geodesy》1985,59(2):189-199
After deriving models for changes of coordinates and azimuths due to rotations, the investigation considers methods for modeling
terrestrial orientation in adjustments of geodetic networks. If a misorientation of a geodetic network exists, this can be
due to systematic errors in astronomic longitude or in astronomic azimuth, or in both. A separation of these two effects is
not possible in practice. The initial azimuth at the datum origin contributes to the orientation only as much as any other
azimuth of the same weight. 相似文献
17.
中国大地测量的数据处理要科学界定潮汐改正计算 总被引：3，自引：1，他引：3
陈俊勇 《武汉大学学报(信息科学版)》2003,28(6):633-635
中国大地测量的现行规范细则中 ,凡涉及潮汐改正计算的都采用全潮汐改正 ,所以相应的数据处理和大地成果就相应于无潮汐值 ,如无潮汐重力值、无潮汐水准高、无潮汐垂线偏差、无潮汐高程异常值 ,甚至由此涉及无潮汐地壳等。这项改正曾经受到 1979年国际大地测量协会 (IAG)堪培拉 (Canberra)大会有关决议的支持 ,但随后不久 ,IAG就作了改正 ,在 1983年汉堡 (Hamburg)大会上仍以决议形式修正了它原来的意见 ,转而对零潮汐改正表示支持。国际大地测量界对潮汐改正的研究几经反复 ,近十年来已取得了比较一致的意见 ,即认为采用零潮汐改正是比较科学的 ,特别是对以陆地国土为主的国家更为合适。因此 ,中国在制定新的大地测量基准的有关条例和相应的各种大地规范细则时 ,应及时修正原来的无潮汐改正的规定 ,确定采用零潮汐改正 ,使全国在这方面的数据处理和所得大地成果纳入更为科学的轨道 相似文献
18.
We can presently construct two independent time series of sea level, each at a precision of a few centimeters, from Geosat
(1985–1988) and TOPEX/Poseidon (1992–1995) collinear altimetry. Both are based on precise satellite orbits computed using
a common geopotential model, JGM-2 (Nerem et al. 1994). We have attempted to connect these series using Geosat-T/P crossover
differences in order to assess long-term ocean changes between these missions. Unfortunately, the observed result are large-scale
sea level differences which appear to be due to a combination of geodetic and geopotential error sources. The most significant
geodetic component seems to be a coordinate system bias for Geosat sea level (relative to T/P) of −7 to −9 cm in the y-axis (towards the Eastern Pacific). The Geosat-T/P sea height differences at crossovers (with JGM-2 orbits) probably also
contain stationary geopotential-orbit error of about the same magnitude which also distort any oceanographic interpretation
of the observed changes. We also found JGM-3 Geosat orbits have not resolved the datum errors evident from the JGM-2 Geosat
-T/P results. We conclude that the direct altimetric approach to accurate determination of sea level change using Geosat and
T/P data still depends on further improvement in the Geosat orbits, including definition of the geocenter.
Received: 11 March 1996; Accepted: 19 September 1996 相似文献
19.
Global height system unification with GOCE: a simulation study on the indirect bias term in the GBVP approach 总被引：4，自引：2，他引：2
One of the main objectives of ESA’s Gravity Field and Steady-State Ocean Circulation mission GOCE (Gravity field and steady-state ocean circulation mission, 1999) is to allow global unification of height systems by directly providing potential differences between benchmarks in different height datum zones. In other words, GOCE provides a globally consistent and unbiased geoid. If this information is combined with ellipsoidal (derived from geodetic space techniques) and physical heights (derived from leveling/gravimetry) at the same benchmarks, datum offsets between the datum zones can be determined and all zones unified. The expected accuracy of GOCE is around 2–3 cm up to spherical harmonic degree n max ≈ 200. The omission error above this degree amounts to about 30 cm which cannot be neglected. Therefore, terrestrial residual gravity anomalies are necessary to evaluate the medium and short wavelengths of the geoid, i.e. one has to solve the Geodetic Boundary Value Problem (GBVP). The theory of height unification by the GBVP approach is well developed, see e.g. Colombo (A World Vertical Network. Report 296, Department of Geodetic Science and Surveying, 1980) or Rummel and Teunissen (Bull Geod 62:477–498, 1988). Thereby, it must be considered that terrestrial gravity anomalies referring to different datum zones are biased due to the respective datum offsets. Consequently, the height reference surface of a specific datum zone deviates from the unbiased geoid not only due to its own datum offset (direct bias term) but is also indirectly affected by the integration of biased gravity anomalies. The latter effect is called the indirect bias term and it considerably complicates the adjustment model for global height unification. If no satellite based gravity model is employed, this error amounts to about the same size as the datum offsets, i.e. 1–2 m globally. We show that this value decreases if a satellite-only gravity model is used. Specifically for GOCE with n max ≈ 200, the error can be expected not to exceed the level of 1 cm, allowing the effect to be neglected in practical height unification. The results are supported by recent findings by Gatti et al. (J Geod, 2012). 相似文献