共查询到20条相似文献，搜索用时 46 毫秒
1.
Modelling the fine-structure of the geoid: Methods,data requirements and some results 总被引：2，自引：0，他引：2
Rene Forsberg 《Surveys in Geophysics》1993,14(4-5):403-418
The requirements for precise geoid models on local and regional scales have increased in recent years, primarily due to the ongoing developments in height determination by GPS on land, but also due to oceanographic requirements in using satellite altimetry for recovering dynamic sea-surface topography. Suitable methods for geoid computations from gravity data include Stokes integration, FFT methods, and least-squares collocation. Especially the FFT methods are efficient in handling large amounts of gravity data, and new variants of the methods taking earth curvature rigorously into account provide attractive methods for obtaining continental-scale, high-resolution geoid models. The accuracy of such models may be from 2–5 cm locally, to 50–100 cm on regional scales, depending on gravity data coverage, long wave-length gravity field errors, and datum problems. When approaching the cm-level geoid basic geoid definition questions (geoid or quasigeoid?) become very significant, especially in rugged areas. In the paper the geoid modelling methods and problems are reviewed, and some investigations on local data requirements for cm-level geoid prediction are presented. Some actual results are presented from Scandinavia, where a recent regional high-resolution geoid model yields apparent accuracies of 2–10 cm over GPS baselines of 50 to 2000 km. 相似文献
2.
Ali Kiliçoğlu Ahmet Direnç Hasan Yildiz Murat Bölme Bahadir Aktuğ Mehmet Simav Onur Lenk 《Studia Geophysica et Geodaetica》2011,55(4):557-578
Turkish regional geoid models have been developed by employing a reference earth gravitational model, surface gravity observations
and digital terrain models. The gravimetric geoid models provide a ready transformation from ellipsoidal heights to the orthometric
heights through the use of GPS/leveling geoid heights determined through the national geodetic networks. The recent gravimetric
models for Turkish territory were computed depending on OSU91 (TG-91) and EGM96 (TG-03) earth gravitational models. The release
of the Earth Gravitational Model 2008 (EGM08), the collection of new surface gravity observations, the advanced satellite
altimetry-derived gravity over the sea, and the availability of the high resolution digital terrain model have encouraged
us to compute a new geoid model for Turkey. We used the Remove-Restore procedure based on EGM08 and applied Residual Terrain
Model (RTM) reduction of the surface gravity data. Fast Fourier Transformation (FFT) was then used to obtain the residual
quasigeoid from the reduced gravity. We restored the individual contributions of EGM08 and RTM to the whole quasi-geoid height
(TQG-09). Since the Helmert orthometric height system is adopted in Turkey, the quasi-geoid model (TQG-09) was then converted
to the geoid model (TG-09) by making use of Bouguer gravity anomalies and digital terrain model. After all we combined a gravimetric
geoid model with GPS/leveling geoid heights in order to obtain a hybrid geoid model (THG-09) (or a transformation surface)
to be used in GPS applications. The RMS of the post-fit residuals after the combination was found to be ± 0.95 cm, which represents
the internal precision of the final combination. And finally, we tested the hybrid geoid model with GPS/leveling data, which
were not used in the combination, to assess the external accuracy. Results show that the external accuracy of the THG-09 model
is ± 8.4 cm, a precision previously not achieved in Turkey until this study. 相似文献
3.
De Lacy M.C. Rodríguez-Caderot G. Marín E. Ruiz A. Borque M.J. Gil A.J. Biagi L. 《Studia Geophysica et Geodaetica》2001,45(1):55-66
Two new GPS surveys have been carried out to check the accuracy of an existing gravimetric geoid in a test area located in northern Andalusia (Spain). The fast collocation method and the remove-restore procedure have been used for the computation of the quasigeoid model. The Spanish height system is based on orthometric heights, so the gravimetrically determined quasigeoid has been transformed to a geoid model and then compared to geoid undulations provided by GPS and levelling at benchmarks belonging to the Spanish first-order levelling network. The discrepancies between the gravimetric solution and GPS/levelling undulations amount to ±2 cm for one survey and ±5 cm for another after fitting a plane to the geoid model. 相似文献
4.
The continuous efforts on establishment and modernization of the geodetic control in Turkey include a number of regional geoid
models that have been determined since 1976. The recently released gravimetric Geoid of Turkey, TG03, is used in geodetic
applications where GPS-heights need to be converted to the local vertical datum. To reach a regional geoid model with improved
accuracy, the selection of the appropriate global geopotential model is of primary importance. This study assesses the performance
of a number of recent satellite-only and combined global geopotential models (GGMs) derived from CHAMP and GRACE missions’
data in comparison to the older EGM96 model, which is the underlying reference model for TG03. In this respect, gravity anomalies
and geoid heights from the global geopotential models were compared with terrestrial gravity data and low-pass filtered GPS/levelling
data, respectively. Also, five new gravimetric geoid models, computed by the Fast Fourier Transform technique using terrestrial
gravity data and the geopotential models, were validated at the GPS/levelling benchmarks. The findings were also compared
with the validation results of the TG03 model.
The tests showed that as it was expected any of the high-degree combined models (EIGEN-CG03C, EIGEN-GL04C, EGM96) can be employed
for determining the gravity anomalies over Turkey. In the west of Turkey, EGM96 and EIGEN-CHAMP03S fit the GPS/levelling surface
better. However, all the tested GGMs revealed equal performance when they were employed in gravimetric geoid modelling after
de-trending the gravimetric geoid model with corrector surface fitting. The new geoid models have improved accuracy (after
fit) compared to TG03. 相似文献
5.
Improved determination of heights using a conversion surface by combining gravimetric quasi-geoid/geoid and GPS-levelling height differences 总被引：2，自引：0，他引：2
The quasi-geoid/geoid can be determined from the Global Positioning System (GPS) ellipsoidal height and the normal/orthometric
heights derived from levelling (GPS-levelling). In this study a gravimetric quasigeoid and GPS-levelling height differences
are combined to develop a new surface, suitable for “levelling” by GPS. This new surface provides better conversion of GPS
ellipsoidal heights to the national normal heights. Different combining procedures, a four-parameter solution, linear and
cubic splines interpolations, as well as the least-squares collocation method were investigated and compared over entire Norway.
More than 1700 GPS-levelling stations were used in this study. The combined surface provides significant accuracy improvement
for the normal height transformation of GPS height data, as demonstrated by the post-fitting residuals. The best solution,
based on the least-squares collocation, provided a conversion surface for the transformation of GPS heights into normal height
in Norway with an accuracy of about 5 cm. 相似文献
6.
研究和实施了由卫星测高数据计算垂线偏差，用莫洛 金斯基（Molodensky）公式反演 大地水准面高，由此求得我国海域大地水准面高. 为了检核，将测高垂线偏差利用逆维宁迈 纳斯（Vening Meinesz）公式反演重力异常，与海上船测重力值进行了外部检核；同时还用 司托克斯（Stokes）公式，将上述反演的重力异常计算大地水准面高，与莫洛金斯基公式直 接解得的相应结果进行比较作为内部检核. 在积分计算中充分应用了FFT的严格公式.由重力和GPS水准数据确定的陆地大地水准面，和主要由卫星测高数据确定的海洋大地水准 面，二者之间一般都存在以系统误差为主的拼接差，本文分析了产生这一现象的主要原因, 并结合我国在陆海大地水准面拼接区重力资料稀疏的实际，提出了新的拼接技术，最后将拟 合参数校正中国全部海域的重 力大地水准面，以最大限度地削弱拼接点和制约测高海洋大地水准面可能存在的系统误差. 相似文献
7.
Blázquez E.B. Gil A.J. Rodríguez-Caderot G. de Lacy M.C. Ruiz J.J. 《Studia Geophysica et Geodaetica》2003,47(3):511-520
In 1991 the first determination of a gravimetric geoid in a test area in central Spain was computed by using least square collocation. In 1995 a gravimetric geoid in the Iberian Peninsula, Ibergeo95, was calculated by FFT. Nowadays an improved geoid of Andalusia, ANDALUSGeoid2002, has been computed by fast collocation procedure and remove-restore technique in the GRS80 Reference System. The computations have been done from 16562 free-air gravity anomaly data set, obtained from IGN (Instituto Geográfico Nacional) and BGI (International Gravity Bureau), the Earth Gravity Model EGM96 and detailed (100 m × 100 m), coarse (5 km × 5 km) and reference (20 km × 20 km) digital terrain models. Relative carrier-phase GPS measurements at 69 benchmarks of the Spanish Levelling Network in Andalusia have been done. The standard deviations of differences between ANDALUSGeoid2002 and GPS/levelling undulations after fitting the tilt have been ± 11 cm, ± 39 cm and ± 38 cm in western, eastern and whole Andalusia, respectively. The ANDALUSGeoid2002 shows an improvement of Ibergeo95 in this territory. 相似文献
8.
Kostelecký J. Kostelecký J. Pešek I. Šimek J. Švábenský O. Weigel J. Zeman A. 《Studia Geophysica et Geodaetica》2004,48(3):503-518
Several quasigeoid models for the Czech Republic have been developed for different purposes since mid-seventies using different data sources: gravimetric, astronomical and GPS/levelling observations, as well as data gained from the territories of neighbouring countries. Two of the recent solutions, namely the VUGTK96 quasigeoid obtained from heterogeneous data and gravimetric quasigeoid CR2000 are described and compared. Accuracies of the models were estimated with the help of accuracy characteristics resulting from the processing, by comparison with GPS/levelling results available for most of the territory, and, finally, tested on a special GPS/levelling profile across the steepest slope of the quasigeoid surface in the south-eastern part of the territory. It is shown that the CR2000 gravimetric quasigeoid is suitable for transformation of ellipsoidal GPS heights to the gravity related heights with an accuracy of 3 cm. 相似文献
9.
A new gravimetric, satellite altimetry, astronomical ellipsoidal boundary value problem for geoid computations has been developed and successfully tested. This boundary value problem has been constructed for gravity observables of the type (i) gravity potential, (ii) gravity intensity (i.e. modulus of gravity acceleration), (iii) astronomical longitude, (iv) astronomical latitude and (v) satellite altimetry observations. The ellipsoidal coordinates of the observation points have been considered as known quantities in the set-up of the problem in the light of availability of GPS coordinates. The developed boundary value problem is ellipsoidal by nature and as such takes advantage of high precision GPS observations in the set-up. The algorithmic steps of the solution of the boundary value problem are as follows:
- - Application of the ellipsoidal harmonic expansion complete up to degree and order 360 and of the ellipsoidal centrifugal field for the removal of the effect of global gravity and the isostasy field from the gravity intensity and the astronomical observations at the surface of the Earth.
- - Application of the ellipsoidal Newton integral on the multi-cylindrical equal-area map projection surface for the removal from the gravity intensity and the astronomical observations at the surface of the Earth the effect of the residual masses at the radius of up to 55 km from the computational point.
- - Application of the ellipsoidal harmonic expansion complete up to degree and order 360 and ellipsoidal centrifugal field for the removal from the geoidal undulations derived from satellite altimetry the effect of the global gravity and isostasy on the geoidal undulations.
- - Application of the ellipsoidal Newton integral on the multi-cylindrical equal-area map projection surface for the removal from the geoidal undulations derived from satellite altimetry the effect of the water masses outside the reference ellipsoid within a radius of 55 km around the computational point.
- - Least squares solution of the observation equations of the incremental quantities derived from aforementioned steps in order to obtain the incremental gravity potential at the surface of the reference ellipsoid.
- - The removed effects at the application points are restored on the surface of reference ellipsoid.
- - Application of the ellipsoidal Bruns’ formula for converting the potential values on the surface of the reference ellipsoid into the geoidal heights with respect to the reference ellipsoid.
- - Computation of the geoid of Iran has successfully tested this new methodology.
Keywords: Geoid computations; Ellipsoidal approximation; Ellipsoidal boundary value problem; Ellipsoidal Bruns’ formula; Satellite altimetry; Astronomical observations 相似文献
10.
11.
Doñana National Park is an area of approximately 500 km2 located on the SW coast of Spain that shows one of the greatest geoid gradients on the entire Iberian Peninsula, due to its peculiar tectonic characteristics. So, it is necessary to elaborate an accurate geoid model that can be used with GPS for precise surveying, since the existing ones are insufficient, due to their poor resolution and their limited adaptation to a small area with such a strong gradient. The least squares prediction method was tested in order to obtain the undulation from GPS/orthometric points. The results obtained were unsatisfactory because of the strong geoid gradient. In order to improve accuracy the remove-restore technique was used. Global geopotential model EIGEN-CG01C and a Digital Elevation Model (DEM) with a 25 × 25 m resolution and an accuracy better than 3 m were used. Thus, the final geometrical geoid obtained reaches the precision required by other disciplines (3 cm in any point within the Park). Particularly, the geoid model has allowed for the acquisition of a precision DEM that is essential to formulate a hydrodynamic model for the Doñana marsh functions. 相似文献
12.
Progress in technology for the 2005 height determination of Qomolangma Feng (Mt. Everest) 总被引：2，自引：0，他引：2
Qomolangma Feng——Mt. Everest (QF in shorter) is located in the east part of the China-Nepal boundary. QF is the highest mountain in China, also in the world. It lies in the collision zone along the boundary of Eurasian and Indian plates. It is one of focuses in geo- sciences study[1―7]. The northern slope area of the QF (QF area in shorter) is in Tibet, China, and the altitude of snow line in the QF area is around 6000 m. Spring in the QF area is March, April and May every year, a… 相似文献
13.
14.
15.
The EGM08 geopotential model complete to degree and order 2159 was used in a remove-compute-restore (RCR) method for the geoid
computation in the State of Rio de Janeiro, Brazil. Terrain and indirect effect corrections were computed using a 6-arcsec
resolution DTE, derived from the TOPODATA Project (Shuttle Radar Topography Mission data) raised by the National Institute
for Space Research. INPE, Brazil. We applied Voronoi/Delaunay discretisations for discrete Stokes integration. In these schemes,
target area is partitioned into polygons/triangles, respectively, and the computation is carried out by point-wise numerical
integration and no gridding is mandatory. For both procedures, the cells were produced using either observed gravity data
combined with gridded Bouguer derived information. Particularly in Delaunay scheme, as the gravity anomalies are interpolated
into the triangular cells, and geoid undulations are computed for their vertices, Stokes function singularity was gone. Externally
estimated errors resulting from a comparison with GPS/leveling data were presented for both the schemes and classical ones,
as well as for the EGM08 undulations. They yielded RMS differences equal to 0.105 m, 0.110 m, 0.110 m, 0.115 m and 0.228 m,
respectively, for Voronoi, Delaunay, Voronoi/Delaunay with gridded-data alone and EGM08, computed between 32 GPS/leveling
points. 相似文献
16.
From the late 1990s, many studies on local geoid construction have been made in South Korea. However, the precision of the previous geoid has remained about 15 cm due to distribution and quality problems of gravity and GPS/levelling data. Since 2007, new land gravity data and GPS/levelling data have been obtained through many projects such as the Korean Land Spatilaization, Unified Control Point and Gravity survey on the Benchmark. The newly obtained data are regularly distributed to a certain degree and show much better improvement in their quality. In addition, an airborne gravity survey was conducted in 2008 to cover the Korean peninsula (South Korea only). Therefore, it is expected that the precision of the geoid could be improved. In this study, the new South Korean gravimetric geoid and hybrid geoid are presented based on land, airborne, ship‐borne, altimeter gravity data, geopotential model and topographic data. As for the methodology, the general remove‐restore approach was applied with the best chosen parameters in order to produce a precise local geoid. The global geopotential model EGM08 was used to remove the low‐frequency components using degree and order up to 360 and the short wavelength part of the gravity signal was dealt with by using the Shuttle Radar Topography Mission data. The parameters determined empirically in this study include for Stokes’ integral 0.5° and for Wong‐Gore kernel 110–120°, respectively and 10 km for both the Bjerhammar sphere depth and attenuation factor. The final gravimetric geoid in South Korea ranges from 20–31 m with a precision of 5.45 cm overall compared to 1096 GPS/levelling data. In addition, the South Korean hybrid geoid produces 3.46 cm and 3.92 cm for degrees of fitness and precision, respectively and a better statistic of 2.37 cm for plain and urban areas was achieved. The gravimetric and hybrid geoids are expected to improve further when the refined land gravity data are included in the near future. 相似文献
17.
Comparison of the qualities of recent global and local gravimetric geoid models in Iran 总被引：1，自引：0，他引：1
A number of regional gravimetric geoid models have recently been determined for the Iran area, and a common problem is to select the best model, e.g. for engineering applications. A related problem is that in order to improve the local geoid models, the selection of the best Global Geopotential Model (GGM) model for the region is essential, to be used in a combined solution from GGM and local gravimetric data. We discuss these problems by taking advantage of 260 GPS/levelling points as an external tool for validation of different global and local geoid models in the absolute and relative senses. By using relative comparisons of the height differences between precise levelling and GPS/geoid models we avoid possible unknown systematic effects between the different types of observables.The study shows that the combination of the newly released GRACE model (GGM02C) with EGM96 geoid model fits the GPS/levelling data in Iran with the best absolute and relative accuracy among the GGMs. Among the local geoid models, the newly gravimetric geoid model IRG04 agrees considerably better with GPS/levelling than any of the other recent local geoid models. Its rms fit with GPS/levelling is 55 cm. Hence, we strongly recommend the use of this new model in any surveying engineering or GPS/levelling projects in the area. 相似文献
18.
Firstly, the new single and combined error models applied to estimate the cumulative geoid height error are efficiently produced by the dominating error sources consisting of the gravity gradient of the satellite-equipped gradiometer and the orbital position of the space-borne GPS/GLONASS receiver using the power spectral principle. At degree 250, the cumulative geoid height error is 1.769 × 10?1 m based on the new combined error model, which preferably accords with a recovery accuracy of 1.760 ×10?1 m from the GOCE-only Earth gravity field model GO_CONS_GCF_2_TIM_R2 released in Germany. Therefore, the new combined error model of the cumulative geoid height is correct and reliable in this study. Secondly, the requirements analysis for the future GOCE Follow-On satellite system is carried out in respect of the preferred design of the matching measurement accuracy of key payloads comprising the gravity gradient and orbital position and the optimal selection of the orbital altitude of the satellite. We recommend the gravity gradient with an accuracy of 10?13?10?15 /s2, the orbital position with a precision of 1-0.1 cm and the orbital altitude of 200-250 km in the future GOCE Follow-On mission. 相似文献
19.
Lars E. Sj?berg 《Studia Geophysica et Geodaetica》2012,56(4):929-933
Recently it was proved that the classical formula for computing the geoid to quasigeoid separation (GQS) by the Bouguer gravity anomaly needs a topographic correction. Here we generalize the modelling of the GQS not only to Bouguer types of anomalies, but also to arbitrary reductions of topographic gravity. Of particular interest for practical applications should be isostatic and Helmert types of reductions, which provide smaller and smoother components, more suitable for interpolation and calculation, than the Bouguer reduction. 相似文献
20.
The Earth’s asthenosphere and lower continental crust can regionally have viscosities that are one to several orders of magnitude smaller than typical mantle viscosities. As a consequence, such shallow low-viscosity layers could induce high-harmonic (spherical harmonics 50–200) gravity and geoid anomalies due to remaining isostasy deviations following Late-Pleistocene glacial isostatic adjustment (GIA). Such high-harmonic geoid and gravity signatures would depend also on the detailed ice and meltwater loading distribution and history.ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission, planned for launch in Summer 2008, is designed to map the quasi-static geoid with centimeter accuracy and gravity anomalies with milligal accuracy at a resolution of 100 km or better. This might offer the possibility of detecting gravity and geoid effects of low-viscosity shallow earth layers and differences of the effects of various Pleistocene ice decay scenarios. For example, our predictions show that for a typical low-viscosity crustal zone GOCE should be able to discern differences between ice-load histories down to length scales of about 150 km.One of the major challenges in interpreting such high-harmonic, regional-scale, geoid signatures in GOCE solutions will be to discriminate GIA-signatures from various other solid-earth contributions. It might be of help here that the high-harmonic geoid and gravity signatures form quite characteristic 2D patterns, depending on both ice load and low-viscosity zone model parameters. 相似文献