Geoid undulation modelling and interpretation at Ladak, NW Himalaya using GPS and levelling data     

P. Banerjee  G. R. Foulger  Satyaprakash  C. P. Dabral 《Journal of Geodesy》1999,73(2):79-86

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   

On the adjustment of combined GPS/levelling/geoid networks   总被引：12，自引：7，他引：5  

C. Kotsakis  M. G. Sideris 《Journal of Geodesy》1999,73(8):412-421

A detailed treatment of adjustment problems in combined global positioning system (GPS)/levelling/geoid networks is given. The two main types of `unknowns' in this kind of multi-data 1D networks are usually the gravimetric geoid accuracy and a 2D spatial field that describes all the datum/systematic distortions among the available height data sets. An accurate knowledge of the latter becomes especially important when we consider employing GPS techniques for levelling purposes with respect to a local vertical datum. Two modelling alternatives for the correction field are presented, namely a pure deterministic parametric model, and a hybrid deterministic and stochastic model. The concept of variance component estimation is also proposed as an important statistical tool for assessing the actual gravimetric geoid noise level and/or testing a priori determined geoid error models. Finally, conclusions are drawn and recommendations for further study are suggested. Received: 9 September 1998 / Accepted: 8 June 1999  相似文献   

The CARIB97 high-resolution geoid height model for the Caribbean Sea     

D. A. Smith  H. J. Small 《Journal of Geodesy》1999,73(1):1-9

A 2×2 arc-minute resolution geoid model, CARIB97, has been computed covering the Caribbean Sea. The geoid undulations refer to the GRS-80 ellipsoid, centered at the ITRF94 (1996.0) origin. The geoid level is defined by adopting the gravity potential on the geoid as W ₀=62 636 856.88 m²/s² and a gravity-mass constant of GM=3.986 004 418×10¹⁴ m³/s². The geoid model was computed by applying high-frequency corrections to the Earth Gravity Model 1996 global geopotential model in a remove-compute-restore procedure. The permanent tide system of CARIB97 is non-tidal. Comparison of CARIB97 geoid heights to 31 GPS/tidal (ITRF94/local) benchmarks shows an average offset (h–H–N) of 51 cm, with an Root Mean Square (RMS) of 62 cm about the average. This represents an improvement over the use of a global geoid model for the region. However, because the measured orthometric heights (H) refer to many differing tidal datums, these comparisons are biased by localized permanent ocean dynamic topography (PODT). Therefore, we interpret the 51 cm as partially an estimate of the average PODT in the vicinity of the 31 island benchmarks. On an island-by-island basis, CARIB97 now offers the ability to analyze local datum problems which were previously unrecognized due to a lack of high-resolution geoid information in the area. Received: 2 January 1998 / Accepted: 18 August 1998  相似文献   

Calculation of geoid undulations and gravity anomalies in the Northwest Pacific by using the Topex/Poseidon and Geosat altimeter data     

Pan Jiayi  Wang Junqin  Wang Yanfeng  Zhang Xinmei  Yuan Yeli  Zheng Quan''an 《海洋学报(英文版)》1999,18(4):523-533

INTRODUCTIONThegeoidistheiargeopotentials~econfidingmostlywiththemeanseasurfaceandisdenotedastheheightrelativetotheidealelliPSes~eoftheearth.Thegeoidundulationsinglobalaceareupto100m.TheunevenstructureOftheearthgivesrisetotheunevenfeatureofthecitysot...  相似文献   

月亮和太阳的潮汐位产生的地球形变位     

高锡铭  E.Grafarend 《大地测量与地球动力学》1992,(3)

采用径向成层的地球模型计算由月亮和太阳的潮汐位所产生的地球形变位。分析的基本出发点是牛顿万有引力位是由随时间变化的质量密度增量产生的;由质量守恒定律,质量密度增量来自未挠动的质量密度的散度和位移矢量场。对质量密度的径向成层模型,采用Dziewonski和Anderson的PREN地球模型(1981);对勒夫(Love)和志田(Shida)数,采用Varga和Denis的模型(1988);对月亮和太阳的潮汐位分别取至3和2阶。计算了地球的形变位。所得结果比用勒夫假定(即δW=K_L(γ)V_(?))计算的结果,相差20％。本文给出了详细的数字结果和讨论。  相似文献   

Terrain corrections to power 3 in gravimetric geoid determination     

H. Nahavandchi  L. E. Sjöberg 《Journal of Geodesy》1998,72(3):124-135

In precise geoid determination by Stokes formula, direct and primary and secondary indirect terrain effects are applied for removing and restoring the terrain masses. We use Helmert's second condensation method to derive the sum of these effects, together called the total terrain effect for geoid. We develop the total terrain effect to third power of elevation H in the original Stokes formula, Earth gravity model and modified Stokes formula. It is shown that the original Stokes formula, Earth gravity model and modified Stokes formula all theoretically experience different total terrain effects. Numerical results indicate that the total terrain effect is very significant for moderate topographies and mountainous regions. Absolute global mean values of 5–10 cm can be reached for harmonic expansions of the terrain to degree and order 360. In another experiment, we conclude that the most important part of the total terrain effect is the contribution from the second power of H, while the contribution from the third power term is within 9 cm. Received: 2 September 1996 / Accepted: 4 August 1997  相似文献   

Preliminary geoid over Zambia     

P. Nsombo 《Journal of Geodesy》1998,72(3):144-153

In the determination of the preliminary geoid over Zambia, we compare three methods of the modified Stokes formula: that of Vincent and Marsh, a modified Wong and Gore method, and a modified spectral weighting method, with the final solution being estimated by the modified Wong and Gore procedure. The geoid over Zambia (based on GRS80) is rising from north-east to south-west. It coincides with the reference ellipsoid in the north-western and southern regions of Zambia. The preliminary estimate indicates maximum and minimum values of about 13.7 and −16.8m, respectively. The mean geoid over the area is −2.8m. Formal analysis of global root mean square errors for the three models leads us to conclude that for an integration cap radius of about 3 or less, the modified formula using optimal spectral weighting is superior to the Vincent and Marsh method, and to the modified and unmodified Wong and Gore. Received: 8 October 1996 / Accepted: 25 June 1997  相似文献   

位错引起的大地水准面变化     

孟国杰  刘桂萍 《地震》1998,18(3):274-280

从动态的观点介绍了大地水准的物理意义。用数值分析方法计算了常见的几种断层位错导致的大地水准面局部变化的分布图像,并着 断层位错的倾角与大地水疰同变化 之间的关系。  相似文献   

Ice Mass Balance and Ice Dynamics from Satellite Gravity Missions     

J. Flury 《Earth, Moon, and Planets》2004,94(1-2):83-91

An overview of advances in ice research which can be expected from future satellite gravity missions is given. We compare present and expected future accuracies of the ice mass balance of Antarctica which might be constrained to 0.1–0.3 mm/year of sea level equivalent by satellite gravity data. A key issue for the understanding of ice mass balance is the separation of secular and interannual variations. For this aim, one would strongly benefit from longer uninterrupted time series of gravity field variations (10 years or more). An accuracy of 0.01 mm/year for geoid time variability with a spatial resolution of 100 km would improve the separability of ice mass balance from mass change due to glacial isostatic adjustment and enable the determination of regional variations in ice mass balance within the ice sheets. Thereby the determination of ice compaction is critical for the exploitation of such high accuracy data. A further benefit of improved gravity field models from future satellite missions would be the improvement of the height reference in the polar areas, which is important for the study of coastal ice processes. Sea ice thickness determination and modelling of ice bottom topography could be improved as well.  相似文献   

Einstein Gravity Explorer–a medium-class fundamental physics mission     

S. Schiller  G. M. Tino  P. Gill  C. Salomon  U. Sterr  E. Peik  A. Nevsky  A. Görlitz  D. Svehla  G. Ferrari  N. Poli  L. Lusanna  H. Klein  H. Margolis  P. Lemonde  P. Laurent  G. Santarelli  A. Clairon  W. Ertmer  E. Rasel  J. Müller  L. Iorio  C. Lämmerzahl  H. Dittus  E. Gill  M. Rothacher  F. Flechner  U. Schreiber  V. Flambaum  Wei-Tou Ni  Liang Liu  Xuzong Chen  Jingbiao Chen  Kelin Gao  L. Cacciapuoti  R. Holzwarth  M. P. Heß  W. Schäfer 《Experimental Astronomy》2009,23(2):573-610

The Einstein Gravity Explorer mission (EGE) is devoted to a precise measurement of the properties of space-time using atomic clocks. It tests one of the most fundamental predictions of Einstein’s Theory of General Relativity, the gravitational redshift, and thereby searches for hints of quantum effects in gravity, exploring one of the most important and challenging frontiers in fundamental physics. The primary mission goal is the measurement of the gravitational redshift with an accuracy up to a factor 10⁴ higher than the best current result. The mission is based on a satellite carrying cold atom-based clocks. The payload includes a cesium microwave clock (PHARAO), an optical clock, a femtosecond frequency comb, as well as precise microwave time transfer systems between space and ground. The tick rates of the clocks are continuously compared with each other, and nearly continuously with clocks on earth, during the course of the 3-year mission. The highly elliptic orbit of the satellite is optimized for the scientific goals, providing a large variation in the gravitational potential between perigee and apogee. Besides the fundamental physics results, as secondary goals EGE will establish a global reference frame for the Earth’s gravitational potential and will allow a new approach to mapping Earth’s gravity field with very high spatial resolution. The mission was proposed as a class-M mission to ESA’s Cosmic Vision Program 2015–2025.

S. SchillerEmail:

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