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1.
On the basis of gravity field model (EIGEN_CG01C), together with multi-altimeter data, the improved deflection of the vertical gridded in 2'×2' in China marginal sea and gridded in 5'×5' in the global sea was determined by using the weighted method of along-track least squares, and the accuracy is better than 1.2^# in China marginal sea. As for the quality of the deflection of the vertical, it meets the challenge for the gravity field of high resolution and accuracy, it shows that, compared with the shipboard gravimetry in the sea, the accuracy of the gravity anomalies computed with the marine deflection of the vertical by inverse Vening-Meinesz formula is 7.75 m.s ^-2. 相似文献
2.
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
3.
Prediction of vertical deflections from high-degree spherical harmonic synthesis and residual terrain model data 总被引:6,自引:4,他引:2
Christian Hirt 《Journal of Geodesy》2010,84(3):179-190
This study demonstrates that in mountainous areas the use of residual terrain model (RTM) data significantly improves the
accuracy of vertical deflections obtained from high-degree spherical harmonic synthesis. The new Earth gravitational model
EGM2008 is used to compute vertical deflections up to a spherical harmonic degree of 2,160. RTM data can be constructed as
difference between high-resolution Shuttle Radar Topography Mission (SRTM) elevation data and the terrain model DTM2006.0
(a spherical harmonic terrain model that complements EGM2008) providing the long-wavelength reference surface. Because these
RTM elevations imply most of the gravity field signal beyond spherical harmonic degree of 2,160, they can be used to augment
EGM2008 vertical deflection predictions in the very high spherical harmonic degrees. In two mountainous test areas—the German
and the Swiss Alps—the combined use of EGM2008 and RTM data was successfully tested at 223 stations with high-precision astrogeodetic
vertical deflections from recent zenith camera observations (accuracy of about 0.1 arc seconds) available. The comparison
of EGM2008 vertical deflections with the ground-truth astrogeodetic observations shows root mean square (RMS) values (from
differences) of 3.5 arc seconds for ξ and 3.2 arc seconds for η, respectively. Using a combination of EGM2008 and RTM data for the prediction of vertical deflections considerably reduces
the RMS values to the level of 0.8 arc seconds for both vertical deflection components, which is a significant improvement
of about 75%. Density anomalies of the real topography with respect to the residual model topography are one factor limiting
the accuracy of the approach. The proposed technique for vertical deflection predictions is based on three publicly available
data sets: (1) EGM2008, (2) DTM2006.0 and (3) SRTM elevation data. This allows replication of the approach for improving the
accuracy of EGM2008 vertical deflection predictions in regions with a rough topography or for improved validation of EGM2008
and future high-degree spherical harmonic models by means of independent ground truth data. 相似文献
4.
D. Arabelos 《Journal of Geodesy》1985,59(2):109-123
The evaluation of deflections of the vertical for the area of Greece is attempted using a combination of topographic and astrogeodetic
data. Tests carried out in the area bounded by 35°≤ϕ≤42°, 19°≤λ≤27° indicate that an accuracy of ±3″.3 can be obtained in
this area for the meridian and prime vertical deflection components when high resolution topographic data in the immediate
vicinity of computation points are used, combined with high degree spherical harmonic expansions of the geopotential and isostatic
reduction potential. This accuracy is about 25% better than the corresponding topographic-Moho deflection components which
are evaluated using topographic and Moho data up to 120 km around each station, without any combination with the spherical
harmonic expansion of the geopotential or isostatic reduction potential. The accuracy in both cases is increased to about
2″.6 when the astrogeodetic data available in the area mentioned above are used for the prediction of remaining values. Furthermore
the estimation of datum-shift parameters is attempted using least squares collocation. 相似文献
5.
A new gravimetric geoid model, USGG2009 (see Abbreviations), has been developed for the United States and its territories
including the Conterminous US (CONUS), Alaska, Hawaii, Guam, the Commonwealth of the Northern Mariana Islands, American Samoa,
Puerto Rico and the US Virgin Islands. USGG2009 is based on a 1′ × 1′ gravity grid derived from the NGS surface gravity data
and the DNSC08 altimetry-derived anomalies, the SRTM-DTED1 3′′ DEM for its topographic reductions, and the global geopotential
model EGM08 as a reference model. USGG2009 geoid heights are compared with control values determined at 18,398 Bench Marks
over CONUS, where both the ellipsoidal height above NAD 83 and the Helmert orthometric height above NAVD 88 are known. Correcting
for the ellipsoidal datum difference, this permits a comparison of the geoid heights to independent data. The standard deviation
of the differences is 6.3 cm in contrast to 8.4 cm for its immediate predecessor— USGG2003. To minimize the effect of long-wavelength
errors that are known to exist in NAVD88, these comparisons were made on a state-by-state basis. The standard deviations of
the differences range from 3–5 cm in eastern states to about 6–9 cm in the more mountainous western states. If the GPS/Bench
Marks-derived geoid heights are corrected by removing a GRACE-derived estimate of the long-wavelength NAVD88 errors before
the comparison, the standard deviation of their differences from USGG2009 drops to 4.3 cm nationally and 2–4 cm in eastern
states and 4–8 in states with a maximum error of 26.4 cm in California and minimum of −32.1 cm in Washington. USGG2009 is
also compared with geoid heights derived from 40 tide-gauges and a physical dynamic ocean topography model in the Gulf of
Mexico; the mean of the differences is 3.3 cm and their standard deviation is 5.0 cm. When USGG2009-derived deflections of
the vertical are compared with 3,415 observed surface astro-geodetic deflections, the standard deviation of the differences
in the N–S and E–W components are 0.87′′ and 0.94′′, respectively. 相似文献
6.
Gottfried Gerstbach 《Journal of Geodesy》1988,62(4):541-563
The short wavelength geoid undulations, caused by topography, amount to several decimeters in mountainous areas. Up to now
these effects are computed by means of digital terrain models in a grid of 100–500m. However, for many countries these data are not yet available or their collection is too expensive.
This problem can be overcome by considering the special behaviour of the gravity potential along mountain slopes. It is shown
that 90 per cent of the topographic effects are represented by a simple summation formula, based on the average height differences
and distances between valleys and ridges along the geoid profiles,
δN=[30.H.D.+16.(H−H′).D] in mm/km, (error<10%), whereH, H′, D are estimated in a map to the nearest 0.2km. The formula is valid for asymmetric sides of valleys (H, H′) and can easily be corrected for special shapes. It can be used for topographic refinement of low resolution geoids and for
astrogeodetic projects.
The “slope method” was tested in two alpine areas (heights up to 3800m, astrogeodetic deflection points every 170km
2) and resulted in a geoid accuracy of ±3cm. In first order triangulation networks (astro points every 1000km
2) or for gravimetric deflections the accuracy is about 10cm per 30km. Since a map scale of 1∶500.000 is sufficient, the method is suitable for developing countries, too. 相似文献
7.
Erwin Groten 《Journal of Geodesy》1975,49(1):41-56
The application of a Sartorius 4104 microbalance after Gast in vertical gradiometry was tested. A small mass of about 20 grams
is suspended on thin fibers of different lengths Δℓ≤80 cm. From the weight difference of the small mass obtained at different
levels along the plumb line the corresponding differences of gravity along the plumb line are inferred. The microbalance is
mounted on a steal rack; measurements at constant low pressure (moderate vacuum) show the applicability of the balance as
gravity difference sensor for field work. When environmental effects are further reduced (i,e, temperature is kept constant
within ±0.1°C; pressure is controlled within 0.1 Torr etc.) the resolution of the balance can be fully exploited so a relative
accuracy of ±10−9 should be feasible and for laboratory experiments should be of the order of a few parts in ±10−10.
Vertical gravity gradients as observed on an improved moving platform with a LaCoste model G gravimeter are discussed. New
possibilities of microgravimetry are pointed out.
High precision observations and establishment of a system in an area of tectonic interest for detecting secular gravity changes
are described.
Paper presented at the meeting of the “International Gravity Commission”, Paris, September 1974. 相似文献
8.
Isaac Dadzie 《地球空间信息科学学报》2007,10(1):27-32
A new computational procedure for derivation of marine geoid on a 2.5′×2.5′grid in a non-tidal system over the South China Sea and the Philippine Sea from multi-satellite altimeter sea surface heights is discussed. Single-and dual-satellite crossovers were performed, and components of deflections of the vertical were determined at the crossover positions using Sand-well's computational theory, and gridded onto a 2.5′×2.5′resolution grid by employing the Shepard's interpolation procedure. 2.5′×2.5′grid of EGM96-derived components of deflections of the vertical and geoid heights were then used as reference global geopotential model quantities in a remove-restore procedure to implement the Molodensky-like formula via 1D-FFT technique to predict the geoid heights over the South China Sea and the Philippine Sea from the gridded altimeter-derived components of deflec-tions of the vertical. Statistical comparisons between the altimeter-and the EGM96- derived geoid heights showed that there was a root-mean-square agreement of ±0.35 m between them in a region of less tectonically active geological structures. However, over areas of tectonically active structures such as the Philippine trench, differences of about -19.9 m were obtained. 相似文献
9.
A least-squares prediction method is described to estimate horizontal coordinate distortions at lower order points of a network
using known coordinate differences (NAD27 coordinate distortions Δϕ′s and Δλ′s) at higher order points between NAD27 coordinates
and coordinates derived from a recent (MAY 76), relatively distortion free, adjustment of these points. Empirical autocovariance
functions of Δϕ and Δλ and crosscovariance function between Δϕ and Δλ are derived from some 5,250 data points and modelled
using series of exponential functions. Empirical mean square values of Δϕ and Δλ, which are a measure of the distortions in
NAD27 ϕ and λ, are 0.051 and 0.645 arcsecs2 respectively. The corresponding mean value of the product ΔϕΔλ, which is a measure of the correlation between Δϕ and Δλ,
is 0.056 arcsecs2. The accuracy obtainable for predicted Δϕ and Δλ at an arbitrary point (e.g., lower order station) is a function of the accuracy
and configuration of known Δϕ′s and Δλ′s in the surrounding area. Accuracies obtainable for various types of data configuration
are given. Under favorable conditions taking place in about 60% of cases, accuracies in terms of ms agreement with known values
of 0″.02 (0.6 m) and 0″.01 (0.2 m along parallel at latitude 50°) for the predicted latitude and longitude distortions are
obtainable. Finally, a comparison with a method based on the use of complex polynomials is made.
Presented at International Symposium on Geodetic Networks and Computations, Munich, August–September 1981. 相似文献
10.
An analysis of vertical deflections derived from high-degree spherical harmonic models 总被引:5,自引:4,他引:1
C. Jekeli 《Journal of Geodesy》1999,73(1):10-22
The theoretical differences between the Helmert deflection of the vertical and that computed from a truncated spherical harmonic
series of the gravity field, aside from the limited spectral content in the latter, include the curvature of the normal plumb
line, the permanent tidal effect, and datum origin and orientation offsets. A numerical comparison between deflections derived
from spherical harmonic model EGM96 and astronomic deflections in the conterminous United States (CONUS) shows that correcting
these systematic effects reduces the mean differences in some areas. Overall, the mean difference in CONUS is reduced from
−0.219 arcsec to −0.058 arcsec for the south–north deflection, and from +0.016 arcsec to +0.004 arcsec for the west–east deflection.
Further analysis of the root-mean-square differences indicates that the high-degree spectrum of the EGM96 model has significantly
less power than implied by the deflection data.
Received: 9 December 1997 / Accepted: 21 August 1998 相似文献
11.
Major Mark C Breach MA MSc ARICS RE 《Journal of Geodesy》1985,59(3):221-232
A method of determining azimuth by gyrotheodolite without electronic registration is described. The method requires observations
of time at each instant the moving mark passes a scale division. Thus many observations of time may be achieved in a single
oscillation of the moving mark. The observations when used in the appropriate observation equation may determine azimuth with
a standard error of ±3″ with 2 hours of observations. This assumes knowledge of the additive constant to about 1″.3 and neglects
the effects of dislevelment in the prime vertical. For practical application of the method a time recording device and microcomputer,
such as the Hewlett Packard HP41CV and HP85, are recommended. 相似文献
12.
A wide-angle airborne laser ranging system (WA-ALRS) is developed at the Institut Géographique National (IGN), France, with
the aim of providing a new geodesy technique devoted to large (100 km2) networks with a high density (1 km−2) of benchmarks. The main objective is to achieve a 1-mm accuracy in relative vertical coordinates from aircraft measurements
lasting a few hours. This paper reviews the methodology and analyzes the first experimental data achieved from a specific
ground-based experiment. The accuracy in relative coordinate estimates is studied with the help of numerical simulations.
It is shown that strong accuracy limitations arise with a small laser beam divergence combined with short range measurements
when relatively few simultaneous range data are produced. The accuracy is of a few cm in transverse coordinates and a few
mm in radial coordinates. The results from ground-based experimental data are fairly compatible with these predictions. The
use of a model for systematic errors in the vehicle trajectory is shown to be necessary to achieve such a high accuracy. This
work yields the first complete validation of modelization and methodology of this technique. An accuracy better than 1 mm
and a few mm in vertical and horizontal coordinates, respectively, is predicted for aircraft experiments.
Received: 19 June 1997 / Accepted: 17 February 1998 相似文献
13.
Determination of Geopotential of Local Vertical Datum Surface 总被引:1,自引:0,他引:1
WEI Ziqing JIAO Wenhai 《地球空间信息科学学报》2003,6(1):1-4
1 IntroductionEachcountryoreachgroupofcountriesselectsmeansealev elatadefinedtidegaugeoratagroupofgaugesforitsverti caldatumsurface .Itisrealized ,however,thatthelocalmeansealevelisusuallydepartedfromthegeoid ,whichshouldbetheidealdatumsurfaceforheight,ow… 相似文献
14.
I. N. Tziavos 《Journal of Geodesy》1987,61(2):177-197
Mean gravity anomalies, deflections of the vertical, and a geopotential model complete to degree and order180 are combined in order to determine geoidal heights in the area bounded by [34°≦ϕ≤42°, 18°≦λ≦28°]. Moreover, employing point
gravity anomalies simultaneously with the above data, an attempt is made to predict deflections of the vertical in the same
area. The method used in the computations is least squares collocation. Using empirical covariance functions for the data,
the suitable errors for the different sources of observations, and the optimum cap radius around each point of evaluation,
an accuracy better than±0.60m for geoidal heights and±1″.5 for deflections of the vertical is obtained taking into account existing systematic effects. This accuracy refers to the
comparison between observed and predicted values. 相似文献
15.
Prediction of surface horizontal displacements, and gravity and tilt changes caused by filling the Three Gorges Reservoir 总被引:11,自引:0,他引:11
Horizontal displacements, and gravity and tilt changes induced by filling the Three Gorges Reservoir are modeled using elastic
loading Green functions. When the water surface reaches its highest level, the effects become maximum on the reservoir banks.
The longitudinal and latitudinal components of the horizontal displacements reach −8.2 and 7.7 mm respectively, gravity is
increased by up to 3.4 mGal, and the prime vertical and meridian components of the tilt changes are −7.8 and −17.5 arcseconds
respectively. Accordingly, the filling of the reservoir will influence values observed from global positioning system (GPS),
gravimetry and tilt measurements in the area. The results given can be used to provide important corrections for extracting
earthquake-related signals from observed data.
Received: 19 January 2001 / Accepted: 3 September 2001 相似文献
16.
We examine the electromagnetic coupling of a GPS antenna–monument pair in terms of its simulated affect on long GPS coordinate
time series. We focus on the Earth and Polar Observing System (POLENET) monument design widely deployed in Antarctica and
Greenland in projects interested particularly in vertical velocities. We base our tests on an absolute robot calibration that
included the top ~0.15 m of the monument and use simulations to assess its effect on site coordinate time series at eight
representative POLENET sites in Antarctica over the period 2000.0–2011.0. We show that the neglect of this calibration would
introduce mean coordinate bias, and most importantly for velocity estimation, coordinate noise which is highly sensitive to
observation geometry and hence site location and observation period. Considering only sub-periods longer than 2.5 years, we
show vertical site velocities may be biased by up to ±0.4 mm/year, and biases up to 0.2 mm/year may persist for observation
spans of 8 years. Changing between uniform and elevation-dependent observation weighting alters the time series but does not
remove the velocity biases, nor does ambiguity fixing. The effect on the horizontal coordinates is negligible. The ambiguities
fixed series spectra show noise between flicker and random walk with near-white noise at the highest frequencies, with mean
spectral indices (frequencies <20 cycles per year) of approximately −1.3 (uniform weighting) and −1.4 (elevation-dependent
weighting). While the results are likely highly monument specific, they highlight the importance of accounting for monument
effects when analysing vertical coordinate time series and velocities for the highest precision and accuracy geophysical studies. 相似文献
17.
Pierre Bosser Olivier Bock Christian Thom Jacques Pelon Pascal Willis 《Journal of Geodesy》2010,84(4):251-265
This paper investigates the impact of rapid small-scale water vapor fluctuations on GPS height determination. Water vapor
measurements from a Raman lidar are used for documenting the water vapor heterogeneities and correcting GPS signal propagation
delays in clear sky conditions. We use data from four short observing sessions (6 h) during the VAPIC experiment (15 May–15
June 2004). The retrieval of wet delays from our Raman lidar is shown to agree well with radiosonde retrievals (bias and standard
deviation (SD) were smaller than 1 and 2.8 mm, respectively) and microwave radiometers (from two different instruments, bias
was 6.0/−6.6 mm and SD 1.3/3.8 mm). A standard GPS data analysis is shown to fail in accurately reproducing fast zenith wet
delay (ZWD) variations. The ZWD estimates could be improved when mean post-fit phase residuals were removed. Several methodologies
for integrating zenith lidar observations into the GPS data processing are also presented. The final method consists in using
lidar wet delays for correcting a priori the GPS phase observations and estimating a scale factor for the lidar wet delays
jointly with the GPS station position. The estimation of this scale factor allows correcting for a mis-calibration in the
lidar data and provides in the same way an estimate of the Raman lidar instrument constant. The agreement of this constant
with an independent determination using radiosonde data is at the level of 1–4%. The lidar wet delays were derived by ray-tracing
from zenith pointing measurements: further improvement in GPS positioning is expected from slant path lidar measurements that
would properly account for water vapor anisotropy. 相似文献
18.
Since the publication of the Earth gravitational model (EGM)96 considerable improvements in the observation techniques resulted
in the development of new improved models. The improvements are due to the availability of data from dedicated gravity mapping
missions (CHAMP, GRACE) and to the use of 5′ × 5′ terrestrial and altimetry derived gravity anomalies. It is expected that
the use of new EGMs will further contribute to the improvement of the resolution and accuracy of the gravity and geoid modeling
in continental and regional scale. To prove this numerically, three representative Earth gravitational models are used for
the reduction of several kinds of data related to the gravity field in different places of the Earth. The results of the reduction
are discussed regarding the corresponding covariance functions which might be used for modeling using the least squares collocation
method. The contribution of the EIGEN-GL04C model in most cases is comparable to that of EGM96. However, the big difference
is shown in the case of EGM2008, due not only to its quality but obviously to its high degree of expansion. Almost in all
cases the variance and the correlation length of the covariance functions of data reduced to this model up to its maximum
degree are only a few percentages of corresponding quantities of the same data reduced up to degree 360. Furthermore, the
mean value and the standard deviation of the reduced gravity anomalies in extended areas of the Earth such as Australia, Arctic
region, Scandinavia or the Canadian plains, vary between −1 and +1 and between 5 and 10 × 10−5 ms−2, respectively, reflecting the homogenization of the gravity field on a regional scale. This is very important in using least
squares collocation for regional applications. However, the distance to the first zero-value was in several cases much longer
than warranted by the high degree of the expansion. This is attributed to errors of medium wavelengths stemming from the lack
of, e.g., high-quality data in some area. 相似文献
19.
Any errors in digital elevation models (DEMs) will introduce errors directly in gravity anomalies and geoid models when used
in interpolating Bouguer gravity anomalies. Errors are also propagated into the geoid model by the topographic and downward
continuation (DWC) corrections in the application of Stokes’s formula. The effects of these errors are assessed by the evaluation
of the absolute accuracy of nine independent DEMs for the Iran region. It is shown that the improvement in using the high-resolution
Shuttle Radar Topography Mission (SRTM) data versus previously available DEMs in gridding of gravity anomalies, terrain corrections
and DWC effects for the geoid model are significant. Based on the Iranian GPS/levelling network data, we estimate the absolute
vertical accuracy of the SRTM in Iran to be 6.5 m, which is much better than the estimated global accuracy of the SRTM (say
16 m). Hence, this DEM has a comparable accuracy to a current photogrammetric high-resolution DEM of Iran under development.
We also found very large differences between the GLOBE and SRTM models on the range of −750 to 550 m. This difference causes
an error in the range of −160 to 140 mGal in interpolating surface gravity anomalies and −60 to 60 mGal in simple Bouguer
anomaly correction terms. In the view of geoid heights, we found large differences between the use of GLOBE and SRTM DEMs,
in the range of −1.1 to 1 m for the study area. The terrain correction of the geoid model at selected GPS/levelling points
only differs by 3 cm for these two DEMs. 相似文献
20.
An inverse Poisson integral technique has been used to determine a gravity field on the geoid which, when continued by analytic
free space methods to the topographic surface, agrees with the observed field. The computation is performed in three stages,
each stage refining the previous solution using data at progressively increasing resolution (1o×1o, 5′×5′, 5/8′×5/8′) from a decreasing area of integration. Reduction corrections are computed at 5/8′×5/8′ granularity by
differencing the geoidal and surface values, smoothed by low-pass filtering and sub-sampled at 5′ intervals. This paper discusses
1o×1o averages of the reduction corrections thus obtained for 172 1o×1o squares in western North America.
The 1o×1o mean reduction corrections are predominantly positive, varying from −3 to +15mgal, with values in excess of 5mgal for 26 squares. Their mean andrms values are +2.4 and 3.6mgal respectively and they correlate well with the mean terrain corrections as predicted byPellinen in 1962. The mean andrms contributions from the three stages of computation are: 1o×1o stage +0.15 and 0.7mgal; 5′×5′ stage +1.0 and 1.6mgal; and 5/8′×5/8′ stage +1.3 and 1.8mgal. These results reflect a tendency for the contributions to become larger and more systematically positive as the wavelengths
involved become shorter. The results are discussed in terms of two mechanisms; the first is a tendency for the absolute values
of both positive and negative anomalies to become larger when continued downwards and, the second, a non-linear rectification,
due to the correlation between gravity anomaly and topographic height, which results in the values continued to a level surface
being systematically more positive than those on the topography. 相似文献