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1.
ENVISAT测高卫星沿轨大地水准面梯度的海洋垂线偏差法研究 总被引:1,自引:0,他引:1
研究了利用沿轨大地水准面梯度数据计算海洋垂线偏差的最小二乘法,首先对ENVISAT测高数据进行各项地球物理改正得到近似测高大地水准面,然后计算沿轨大地水准面的梯度,接着用最小二乘法计算格网垂线偏差东西分量和南北分量的平均值。最后,用该方法计算了南中国海区域及其邻近海域(4°N~25°N,104°E~120°E)的5′×5′垂线偏差南北分量和东西分量,其精度优于7″,并与EGM96模型计算的垂线偏差值进行了比较,证明了该方法的有效性。 相似文献
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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
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卫星测高与卫星重力对洋流的研究 总被引:2,自引:0,他引:2
卫星测高与卫星重力的发展为进一步研究洋流提供了前所未有的机遇。本文从EGM 96 ,GGM0 1与未来的GOCE任务获取的高精度高分辨率海洋大地水准面的角度对洋流的研究方法与可行性进行了分析 相似文献
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Marine gravity and geoid determination by optimal combination of satellite altimetry and shipborne gravimetry data 总被引:2,自引:0,他引:2
. Satellite altimetry derived geoid heights and marine gravity anomalies can be combined to determine a detailed gravity field
over the oceans using the least-squares collocation method and spectral combination techniques. Least-squares collocation,
least-squares adjustment in the frequency domain and input-output system theory are employed to determine the gravity field
(both geoid and anomalies) and its errors. This paper intercompares these three techniques using simulated data. Simulation
studies show that best results are obtained by the input-output system theory among the three prediction methods. The least-squares
collocation method gives results which are very close to but a little bit worse than those obtained using input-output system
theory. This slightly poorer performance of the least-squares collocation method can be explained by the fact that it uses
isotropic structured covariance (thus approximate signal PSD information) while the system theory method uses detailed signal
PSD information. The method of least-squares adjustment in the frequency domain gives the poorest results among these three
methods because it uses less information than the other two methods (it ignores the signal PSDs). The computations also show
that the least-squares collocation and input-output system theory methods are not as sensitive to noise levels as the least-squares
adjustment in the frequency domain method is.
Received 19 January 1996; Accepted 17 July 1996 相似文献
7.
On the adjustment of combined GPS/levelling/geoid networks 总被引:5,自引:7,他引:5
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
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A detailed accuracy assessment of the geopotential model Jgm3 is made based on independent single- and dual-satellite sea-height
differences at crossovers from altimetry with Jgm3-based orbits. These differences, averaged over long time spans and in latitude
bands, are converted to spectra (latitude-lumped coefficients) by least-squares estimation. The observed error spectra so
obtained are then compared directly to error projections for them from the Jgm3 variance–covariance matrix. It is found from
these comparisons that Jgm3 is generally well calibrated with respect to the crossover altimetry of and between Geosat, TOPEX/Poseidon
(T/P), and Ers 1. Some significant discrepancies at a few lower orders (namely m=1 and 3) indicate a need for further improvement of Jgm3. A companion calibration (by order) of the geopotential model Jgm2
shows its variance–covariance matrix also to be generally well calibrated for the same single- and dual-satellite altimeter
data sets (but based on Jgm2 orbits), except that the error projections for Geosat are too pessimistic. The analysis of the
dual-satellite crossovers reveals possible relative coordinate system offsets (particularly for Geosat with respect to T/P)
which have been discussed previously. The long-term detailed seasonally averaged Geosat sea level with respect to T/P (covering
1985–1996) should be useful in gauging the relative change in sea level between different parts of the ocean over the single
4-year gap between these missions (1988–1992).
Received: 16 February 1998 / Accepted: 25 November 1998 相似文献
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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
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LUO Jia LI Jiancheng CHAO Dingbo 《地球空间信息科学学报》2003,6(1):19-23
1 IntroductionTodeveloptheoceanwidelyanddeeply ,weneedabundantoceaninformation .Asanessentialpartofsuchinformation ,seafloortopographyplaysaveryimportantroleinavarietyofmarineactivities .However,thehighcostforoceanbathymetricsurveyinglimitstheapplicationo… 相似文献
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One-year average satellite altimetry data from the Exact Repeat Missions (ERM) of GEOSAT have been used to determine marine gravity disturbances in the Labrador Sea region using the inverse Hotine approach with FFT techniques. The derived satellite gravity information has been compared to shipboard gravity as well as gravity information derived by least-squares collocation (LSC), GEMT3 and OSU91A geopotential models in the Orphan Knoll area. The RMS and mean differences between satellite and shipboard gravity disturbances are about 8.0 and 2.8 mGal, respectively. There is no significantly difference between the results obtained using FFT and LSC. 相似文献
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Georges Blaha 《Journal of Geodesy》1979,53(3):215-220
A key element in any attempt to achieve a0.1 m precision in geoid representation via satellite altimetry is obtaining an ephemeris of comparable precision, or circumventing
this requirement by adjusting the ephemeris in some way, together with the geoid. The first possibility requires extensive
satellite tracking and involves an enormous number of adjustable parameters in the long arc approach.
The second psssibility allows for a piece-wise treatment of short orbital arcs considered mutually independent, in which slight
adjustments of the state vector parameters can compensate for an inherent modeling error. The main question to be answered
when pondering the possibility of using the short arc adjustment model in SEASAT-A altimetry reductions is whether or not
this method is inherently capable of representing the detailed geoid with0.1 m precision. An analysis of computer simulations provides at least a partial answer to this question by pointing out the necessary
conditions in order to achieve the desired precision; under certain favorable circumstances, not described in detail, these
conditions could prove to be also sufficient. 相似文献
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The geodetic boundary value problem is formulated which uses as boundary values the differences between the geopotential of
points at the surface of the continents and the potential of the geoid. These differences are computed by gravity measurements
and levelling data. In addition, the shape of the geoid over the oceans is assumed to be known from satellite altimetry and
the shape of the continents from satellite results together with three-dimensional triangulation. The boundary value problem
thus formulated is equivalent to Dirichlet's exterior problem except for the unknown potential of the geoid. This constant
is determined by an integral equation for the normal derivative of the gravitational potential which results from the first
derivative of Green's fundamental formula. The general solution, which exists, of the integral equation gives besides the
potential of the geoid the solution of the geodetic boundary value problem. In addition approximate solutions for a spherical
surface of the earth are derived. 相似文献
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G. Blaha 《Journal of Geodesy》1977,51(1):33-45
The short arc adjustment mode makes a determination of the geoid surface possible without the requirement of highly precise
reference orbits. In this mode, the state vector components are subject to adjustment and represent in fact a set of independent
weighted parameters. In a most elementary approach, the radial distance to a satellite point is differentiated with respect
to these parameters and a radial distance to the geoid (r) is differentiated with respect to the earth potential coefficients.
The observed satellite altimetry value (H) is approximately equal to the difference between these two radial distances. In
the present study, a correction is introduced that makes it possible to express the mathematical model for H as accurately
as practicable, good to a few centimeters. With regard to the partial differentiation, it is argued that r, in addition to
being differentiated with respect to the potential coefficients, has to be differentiated also with respect to the state vector
components. This gives rise to a second type of correction. It is shown that for most practical purposes, the ellipsoidal
approximation to the geoid used to compute the above two kinds of corrections is satisfactory. The final results indicate
that actual computation of these corrections is a very simple matter; an eventual upgrading of satellite altimetry computer
programs can thus be accomplished with almost no additional effort. A practical benefit of the presented analysis is faster
convergence in the adjustment which, in some cases, may remove the need for iterated solutions altogether. 相似文献
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A technique is presented for the development of a high-precision and high-resolution mean sea surface model utilising radar
altimetric sea surface heights extracted from the geodetic phase of the European Space Agency (ESA) ERS-1 mission. The methodology
uses a cubic-spline fit of dual ERS-1 and TOPEX crossovers for the minimisation of radial orbit error. Fourier domain processing
techniques are used for spectral optimal interpolation of the mean sea surface in order to reduce residual errors within the
initial model. The EGM96 gravity field and sea surface topography models are used as reference fields as part of the determination
of spectral components required for the optimal interpolation algorithm. A comparison between the final model and 10 cycles
of TOPEX sea surface heights shows differences of between 12.3 and 13.8 cm root mean square (RMS). An un-optimally interpolated
surface comparison with TOPEX data gave differences of between 15.7 and 16.2 cm RMS. The methodology results in an approximately
10-cm improvement in accuracy. Further improvement will be attained with the inclusion of stacked altimetry from both current
and future missions.
Received: 22 December 1999 / Accepted: 6 November 2000 相似文献
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Summary Satellite gradiometry is studied as a means to improve the geoid in local areas from a limited data coverage. Least-squares
collocation is used for this purpose because it allows to combine heterogeneous data in a consistent way and to estimate the
integrated effect of the attenuated spectrum. In this way accuracy studies can be performed in a general and reliable manner.
It is shown that only three second-order gradients contribute significantly to the estimation of the geoidal undulations and
that it is sufficient to have gradiometer data in a 5°×5° area around the estimation point. The accuracy of the geoid determination
is strongly dependent on the degree and order of the reference field used. An accuracy of about ±1 m can be achieved with
a reference field of (12, 12). There is an optimal satellite altitude for each reference field and this altitude may be higher
than 300 km for a field of low degree and order. The influence of measuring errors is discussed and it is shown that only
gradiometer data with accuracies better than ±0.05 E will give a significant improvement of the geoid. Finally, some results
on the combination of satellite gradiometry and terrestrial gravity measurements are given.
The proposed method seems to be well suited for local geoid determinations down to the meter range. It is especially interesting
for unsurveyed and difficult areas because no terrestrial measurements are necessary. Furthermore, it has the practical advantage
that only a local data coverage is needed. 相似文献
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We present a new approach to estimate precise long-term vertical land motion (VLM) based on double-differences of long tide gauge (TG) and short altimetry data. We identify and difference rates of pairs of highly correlated sea level records providing relative VLM estimates that are less dependent on record length and benefit from reduced uncertainty and mitigated biases (e.g. altimeter drift). This approach also overcomes the key limitation of previous techniques in that it is not geographically limited to semi-enclosed seas and can thus be applied to estimate VLM at TGs along any coast, provided data of sufficient quality are available. Using this approach, we have estimated VLM at a global set of 86 TGs with a median precision of 0.7 mm/year in a conventional reference frame. These estimates were compared to previous VLM estimates at TGs in the Baltic Sea and to estimates from co-located Global Positioning System (GPS) stations and Glacial Isostatic Adjustment (GIA) predictions. Differences with respect to the GPS and VLM estimates from previous studies resulted in a scatter of around 0.6 mm/year. Differences with respect to GIA predictions had a larger scatter in excess of 1 mm/year. Until satellite altimetry records reach enough length to estimate precise VLM at each TG, this new approach constitutes a substantial advance in the geodetic monitoring of TGs with major applications in long-term sea level change and climate change studies. 相似文献