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1.
A. M. C. Srivastava 《Journal of Geodesy》1984,58(4):510-517
The astrogeodetic—gravimetric method based on the principle of least—squares solution has been used to determine the geocentric
Indian geodetic datum making use of the available nongeocentric astrogeodetic data and the gravimetric geocentric geoidal
heights in the form of smoothened values. Everett's method of interpolation has been used to obtain the smoothened geoidal
heights at the astrogeodetic stations in India from the available generalized values at 1°×1° corners. The values of the geoidal
height and deflections of the vertical at the geodetic datum Kalianpur H.S. so obtained have the negligible difference from
the values computed earlier by the same method using directly computed gravimetric geoidal heights at the astrogeodetic stations,
indicating that the use of the interpolated values in the astrogeodetic—gravimetric method employed would be an economical
approach of absolute orientation of a nongeocentric system if the gravimetric geoidal heights are available at 1°×1° corners
in the area of interest. 相似文献
2.
Gravity field estimation in geodesy, through linear(ized) least squares algorithms, operates under the assumption of Gaussian
statistics for the estimable part of preselected models. The causal nature of the gravity field is implicitly involved in
its geodetic estimation and introduces the need to include prior model information, as in geophysical inverse problems. Within
the geodetic concept of stochastic estimation, the prior information can be in linear form only, meaning that only data linearly
depending on the estimates can be used effectively. The consequences of the inverse gravimetric problem in geodetic gravity
field estimation are discussed in the context of the various approaches (in model data spaces) which have the common goal
to bring into agreement the statistics between these two spaces. With a simple numerical example of FAA prediction, it is
shown that prior information affects the accuracy of estimates at least equally as the number of input data.
Received: 25 April 1994; Accepted: 15 October 1996 相似文献
3.
J. C. Bhattacharji 《Journal of Geodesy》1973,47(1):65-72
The method of converting geodetic coordinates from a national geodetic reference system into the standard Earth on having
known the geodetic coordinates of at least one station in common with the considered systems, is described in detail; the
orientation of the Standard Earth at the initial station of the national geodetic reference system, is also determined side
by side. For illustration, use has been made of the known coordinates of the Baker-Nunn station at Naini Tal, in India, being
in common with the Indian Everest Spheroid and the Smithsonian Institution Standard Earth C7 system (Veis, 1967). The method advocated is likely to be more precise than the existing ones as it does not assume the parallelism
of axes of reference between the Standard Earth and the national geodetic reference systems which may not necessarily hold
good in actual practice. 相似文献
4.
Bela Szabo 《Journal of Geodesy》1962,36(3):227-242
Three different types of deflection of the vertical components wre computed at a number of selected astronomical stations
in the south central United States.
Astro-geodetic deflections were obtained from the differences between the astronomical and geodetic coordinates of each station.
Gravimetric deflections were computed from isostatic anomalies. The isostatic isoanomaly charts used in this computation were
constructed from data obtained by correcting point values taken from existing free-air isoanomaly charts for the effects of
the Bouguer reduction and the topographic-isostatic reduction. It is felt that this procedure substantially reduces the labor
involved in making isostatic reductions without sacrificing accuracy appreciably.
Topographic-isostatic deflections were computed by Hayford's Method as modified by Orlin.
The differences between the three types of deflection components are compared and conclusions made concerning their accuracy
and utility.
Aerounautical Chart and Information Center 相似文献
5.
Geoid determination using one-step integration 总被引:1,自引:1,他引:0
P. Novák 《Journal of Geodesy》2003,77(3-4):193-206
A residual (high-frequency) gravimetric geoid is usually computed from geographically limited ground, sea and/or airborne gravimetric data. The mathematical model for its determination from ground gravity is based on the transformation of observed discrete values of gravity into gravity potential related to either the international ellipsoid or the geoid. The two reference surfaces are used depending on height information that accompanies ground gravity data: traditionally orthometric heights determined by geodetic levelling were used while GPS positioning nowadays allows for estimation of geodetic (ellipsoidal) heights. This transformation is usually performed in two steps: (1) observed values of gravity are downward continued to the ellipsoid or the geoid, and (2) gravity at the ellipsoid or the geoid is transformed into the corresponding potential. Each of these two steps represents the solution of one geodetic boundary-value problem of potential theory, namely the first and second or third problem. Thus two different geodetic boundary-value problems must be formulated and solved, which requires numerical evaluation of two surface integrals. In this contribution, a mathematical model in the form of a single Fredholm integral equation of the first kind is presented and numerically investigated. This model combines the solution of the first and second/third boundary-value problems and transforms ground gravity disturbances or anomalies into the harmonically downward continued disturbing potential at the ellipsoid or the geoid directly. Numerical tests show that the new approach offers an efficient and stable solution for the determination of the residual geoid from ground gravity data. 相似文献
6.
The determination of gravimetric deflections of the vertical for the area of Greece is attempted by combining a spherical hamonics model and gravity nomalies using the method of least squares collocation. The components of deflections of the vertical are estimated on a grid with spacing 15′ in latitude and 20′ in longitude covering only the continental area of Greece, where a sufficient number of point gravity anomalies is available. In order to test the accuracy of the determination, gravimetric deflections of the vertical are computed at stations where astrogeodetic data are available. The results show that in a large region of rugged topography and irregular potential field, the prediction is possible with a standard deviation of 18% ... 28% of the root mean square variation of the observations, without taking into account the topography. Furthermore, the estimation of some systematic differences between observed and computed deflections of the vertical is attempted. 相似文献
7.
This paper addresses implementation issues in order to apply non-stationary least-squares collocation (LSC) to a practical
geodetic problem: fitting a gravimetric quasigeoid to discrete geometric quasigeoid heights at a local scale. This yields
a surface that is useful for direct GPS heighting. Non-stationary covariance functions and a non-stationary model of the mean
were applied to residual gravimetric quasigeoid determination by planar LSC in the Perth region of Western Australia. The
non-stationary model of the mean did not change the LSC results significantly. However, elliptical kernels in non-stationary
covariance functions were used successfully to create an iterative optimisation loop to decrease the difference between the
gravimetric quasigeoid and geometric quasigeoid at 99 GPS-levelling points to a user-prescribed tolerance. 相似文献
8.
F. L. Clarke 《Journal of Geodesy》1981,55(1):1-16
Comparisons of gravimetric and astrogeodetic deflections of the vertical in the Australian region indicate that the former
are affected by position dependent systematic errors, even after orientation onto the Australian Geodetic Datum. These are
probably due to errors in the predicted mean anomalies for gravimetrically unsurveyed oceanic regions to the east, south and
west of the continent. Deflection component residuals (astrogeodetic minus oriented gravimetric) at 83 control stations are
made the observables in a set of observation equations, based on the Vening Meinesz equations, from which pseudocorrections
to the mean anomalies for a set of arbitrarily selected surface elements are computed. These pseudocorrections compensate
for prediction errors in much larger unsurveyed regions. Their effects on individual deflection components are calculated
using the Vening Meinesz equations. Statistical tests indicate that pseudocorrections computed for four large offshore elements
and six smaller elements in unsurveyed areas produce corrections to the gravimetric deflections which make the ξ and η components
in seconds of arc consistent with normally distributed populations N (0.00, 0.702). 相似文献
9.
The work of a recent Soviet geodetic surveying expedition to the Central Arctic and the Barents Sea off Franz Josef Land is described, with an emphasis on gravimetric surveying and determination of gravimetric control points at the North Pole and at two drifting polar research stations. In addition, glacier fields of Alexander Land (Franz Josef Land) were mapped and keys for their interpretation on space imagery identified. Translated from: Geodeziya i kartografiya, 1988, No. 3, pp. 9-12. 相似文献
10.
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
11.
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
12.
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
13.
Gravity anomalies from satellite altimetry: comparison between computation via geoid heights and via deflections of the vertical 总被引:3,自引:0,他引:3
The accumulation of good quality satellite altimetry missions allows us to have a precise geoid with fair resolution and to compute free air gravity anomalies easily by fast Fourier transform (FFT) techniques.In this study we are comparing two methods to get gravity anomalies. The first one is to establish a geoid grid and transform it into anomalies using inverse Stokes formula in the spectral domain via FFT. The second one computes deflection of the vertical grids and transforms them into anomalies.The comparison is made using different data sets: Geosat, ERS-1 and Topex-Poseidon exact repeat misions (ERMs) north of 30°S and Geosat geodetic mission (GM) south of 30°S. The second method which transforms the geoid gradients converted into deflection of the vertical values is much better and the results have been favourably evaluated by comparison with marine gravity data. 相似文献
14.
With the advent of geodetic satellite missions mapping almost globally the Earth’s gravitational field, new methods and theoretical approaches have been developed and investigated to fully exploit the potential of their new observables. Besides estimating values of numerical coefficients in harmonic series of the gravitational potential, new applications emerged such as data validation and combination. In this contribution, new integral transformations are presented which transform principal components of the terrestrial deflection of the vertical onto disturbing satellite-to-satellite tracking and gradiometric data at altitude. Using spherical approximation, necessary integral kernel functions are derived in both spectral and closed forms. The behaviour of isotropic kernel functions is studied and the new integral transformations are tested in a closed-loop simulation using synthetic terrestrial and satellite data synthesized from a global gravitational model. New integral transformations can be used for data validation and combination purposes. 相似文献
15.
郭俊义 《武汉大学学报(信息科学版)》1993,(3)
本文提出了利用变分法解混合边值问题直接计算位系数的原理。根据这一原理可解第一、第二和第三边值问题的混合边值问题直接求得位系数。利用这一原理可较简单地联合利用经典重力测量(即重力点的平面位置由天文或三角测量确定,高程由水准或三角高程确定)、卫星重力测量(即利用卫星定位技术确定重力点的平面位置和大地高)以及卫星测高数据研究地球的重力场。 相似文献
16.
A. M. C. Srivastava 《Journal of Geodesy》1985,59(3):289-295
The geoid on GRS 67 for the Indian subcontinent has been determined using the geopotential coefficients of degree and order
52 and 180. A broad comparison has also been made between these geoids and the previously determined generalized gravimetric
and detailed astrogeodetic-gravimetric geoids. It has been found that still higher degree and order geopotential coefficient
solutions from adequate reliable terrestrial data are required to achieve precision of geodetic standards. 相似文献
17.
18.
J. C. Bhattacharji 《Journal of Geodesy》1980,54(2):225-233
The Everest spheroid, 1830, in general use in the Survey of India, was finally oriented in an arbitrary manner at the Indian
geodetic datum in 1840; while the international spheroid, 1924, in use for scientific purposes; was locally fitted to the
Indian geoid in 1927. An attempt is here made to obtain the initial values for the Indian geodetic datum in absolute terms
on GRS 67 by least-square solution technique, making use of the available astro-geodetic data in India, and the corresponding
generalised gravimetric values at the considered astro-geodetic points, as derived from the mean gravity anomalies over1°×1° squares of latitude and longitude in and around the Indian sub-continent, and over5° equal area blocks covering the rest of the earth’s surface. The values obtained independently by gravimetric method, were
also considered before actual finalization of the results of the present determination. 相似文献
19.
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
20.
Accuracy analysis of vertical deflection data observed with the Hannover Digital Zenith Camera System TZK2-D 总被引:4,自引:1,他引:3
This paper analyses the accuracy of vertical deflection measurements carried out with the Digital Zenith Camera System TZK2-D,
an astrogeodetic state-of-the-art instrumentation developed at the University of Hannover. During 107 nights over a period
of 3.5 years, the system was used for repeated vertical deflection observations at a selected station in Hannover. The acquired
data set consists of about 27,300 single measurements and covers 276 h of observation time, respectively. For the data collected
at an earlier stage of development (2003 to 2004), the accuracy of the nightly mean values has been found to be about 0′′.10−0′′.12.
Due to applying a refined observation strategy since 2005, the accuracy of the vertical deflection measurements was enhanced
into the unprecedented range of 0′′.05 − 0′′.08. Accessing the accuracy level of 0′′.05 requires usually 1 h of observational
data, while the 0′′.08 accuracy level is attained after 20 min measurement time. In comparison to the analogue era of geodetic
astronomy, the accuracy of vertical deflection observations is significantly improved by about one order of magnitude. 相似文献