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1.
Four different implementations of Stokes' formula are employed for the estimation of geoid heights over Sweden: the Vincent
and Marsh (1974) model with the high-degree reference gravity field but no kernel modifications; modified Wong and Gore (1969)
and Molodenskii et al. (1962) models, which use a high-degree reference gravity field and modification of Stokes' kernel;
and a least-squares (LS) spectral weighting proposed by Sj?berg (1991). Classical topographic correction formulae are improved
to consider long-wavelength contributions. The effect of a Bouguer shell is also included in the formulae, which is neglected
in classical formulae due to planar approximation. The gravimetric geoid is compared with global positioning system (GPS)-levelling-derived
geoid heights at 23 Swedish Permanent GPS Network SWEPOS stations distributed over Sweden. The LS method is in best agreement,
with a 10.1-cm mean and ±5.5-cm standard deviation in the differences between gravimetric and GPS geoid heights. The gravimetric
geoid was also fitted to the GPS-levelling-derived geoid using a four-parameter transformation model. The results after fitting
also show the best consistency for the LS method, with the standard deviation of differences reduced to ±1.1 cm. For comparison,
the NKG96 geoid yields a 17-cm mean and ±8-cm standard deviation of agreement with the same SWEPOS stations. After four-parameter
fitting to the GPS stations, the standard deviation reduces to ±6.1 cm for the NKG96 geoid. It is concluded that the new corrections
in this study improve the accuracy of the geoid. The final geoid heights range from 17.22 to 43.62 m with a mean value of
29.01 m. The standard errors of the computed geoid heights, through a simple error propagation of standard errors of mean
anomalies, are also computed. They range from ±7.02 to ±13.05 cm. The global root-mean-square error of the LS model is the
other estimation of the accuracy of the final geoid, and is computed to be ±28.6 cm.
Received: 15 September 1999 / Accepted: 6 November 2000 相似文献
2.
Apropos laser tracking to GPS satellites 总被引:3,自引:0,他引:3
. Laser tracking to GPS satellites (PRN5 and 6) provides an opportunity to compare GPS and laser systems directly and to combine
data of both in a single solution. A few examples of this are given in this study. The most important results of the analysis
are that (1) daily SLR station coordinate solutions could be generated with a few cm accuracy; (2) coordinates of nine stations
were determined in a 2.3-year-long arc solution; (3) the contribution of laser data on the `SLR-GPS' combined orbit, resulting
from the simultaneous processing of SLR and GPS data, is significant and (4) laser-only orbits have an accuracy of 10–20 cm,
1-day predictions of SLR orbits differ from IGS orbits by about 20–40 cm, 2-day predictions by 50–60 cm.
Received: 1 October 1996 / Accepted: 14 February 1997 相似文献
3.
The 2 arc-minute × 2 arc-minute geoid model (GEOID96) for the United States supports the conversion between North American
Datum 1983 (NAD 83) ellipsoid heights and North American Vertical Datum 1988 (NAVD 88) Helmert heights. GEOID96 includes information
from global positioning system (GPS) height measurements at optically leveled benchmarks. A separate geocentric gravimetric
geoid, G96SSS, was first calculated, then datum transformations and least-squares collocation were used to convert from G96SSS
to GEOID96.
Fits of 2951 GPS/level (ITRF94/NAVD 88) benchmarks to G96SSS show a 15.1-cm root mean square (RMS) around a tilted plane (0.06 ppm,
178∘ azimuth), with a mean value of −31.4 cm (15.6-cm RMS without plane). This mean represents a bias in NAVD 88 from global mean
sea level, remaining nearly constant when computed from subsets of benchmarks. Fits of 2951 GPS/level (NAD 83/NAVD 88) benchmarks
to GEOID96 show a 5.5-cm RMS (no tilts, zero average), due primarily to GPS error. The correlated error was 2.5 cm, decorrelating
at 40 km, and is due to gravity, geoid and GPS errors. Differences between GEOID96 and GEOID93 range from −122 to +374 cm
due primarily to the non-geocentricity of NAD 83.
Received: 28 July 1997 / Accepted: 2 September 1998 相似文献
4.
Based upon a data set of 25 points of the Baltic Sea Level Project, second campaign 1993.4, which are close to mareographic
stations, described by (1) GPS derived Cartesian coordinates in the World Geodetic Reference System 1984 and (2) orthometric
heights in the Finnish Height Datum N60, epoch 1993.4, we have computed the primary geodetic parameter W
0(1993.4) for the epoch 1993.4 according to the following model. The Cartesian coordinates of the GPS stations have been converted
into spheroidal coordinates. The gravity potential as the additive decomposition of the gravitational potential and the centrifugal
potential has been computed for any GPS station in spheroidal coordinates, namely for a global spheroidal model of the gravitational
potential field. For a global set of spheroidal harmonic coefficients a transformation of spherical harmonic coefficients
into spheroidal harmonic coefficients has been implemented and applied to the global spherical model OSU 91A up to degree/order
360/360. The gravity potential with respect to a global spheroidal model of degree/order 360/360 has been finally transformed
by means of the orthometric heights of the GPS stations with respect to the Finnish Height Datum N60, epoch 1993.4, in terms
of the spheroidal “free-air” potential reduction in order to produce the spheroidal W
0(1993.4) value. As a mean of those 25 W
0(1993.4) data as well as a root mean square error estimation we computed W
0(1993.4)=(6 263 685.58 ± 0.36) kgal × m. Finally a comparison of different W
0 data with respect to a spherical harmonic global model and spheroidal harmonic global model of Somigliana-Pizetti type (level
ellipsoid as a reference, degree/order 2/0) according to The Geodesist's Handbook 1992 has been made.
Received: 7 November 1996 / Accepted: 27 March 1997 相似文献
5.
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
6.
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
7.
Lars E. Sjöberg 《Journal of Geodesy》1991,65(4):209-217
In October 1987 a four day satellite GPS campaign was performed over the Åland archipelago to test the possibility of connecting the Swedish and Finnish national height systems. This paper summarizes the gained experiences using 5 WM 101 GPS receivers and the PoPS software.The computing results for the connection between the two height systems are considerably dependent on the choice of geoidal undulation model and systematic error parameter model. Using the NKG Scandinavian geoid 1989, which is probably the most accurate geoid available for the region, and a bias and tilt parameter model the difference between the Swedish RH70 system and the Finnish N60 system is estimated to 11.4 ± 4.0 cm. An independent check is provided by two connecting border bench marks in northern Scandinavia yielding the difference 19.2 ± 4.2 cm. In view of that merely single frequency GPS receivers were used together with the PoPS software, we consider this result most satisfactory. 相似文献
8.
An algorithm for very accurate absolute positioning through Global Positioning System (GPS) satellite clock estimation has
been developed. Using International GPS Service (IGS) precise orbits and measurements, GPS clock errors were estimated at
30-s intervals. Compared to values determined by the Jet Propulsion Laboratory, the agreement was at the level of about 0.1 ns
(3 cm). The clock error estimates were then applied to an absolute positioning algorithm in both static and kinematic modes.
For the static case, an IGS station was selected and the coordinates were estimated every 30 s. The estimated absolute position
coordinates and the known values had a mean difference of up to 18 cm with standard deviation less than 2 cm. For the kinematic
case, data obtained every second from a GPS buoy were tested and the result from the absolute positioning was compared to
a differential GPS (DGPS) solution. The mean differences between the coordinates estimated by the two methods are less than
40 cm and the standard deviations are less than 25 cm. It was verified that this poorer standard deviation on 1-s position
results is due to the clock error interpolation from 30-s estimates with Selective Availability (SA). After SA was turned
off, higher-rate clock error estimates (such as 1 s) could be obtained by a simple interpolation with negligible corruption.
Therefore, the proposed absolute positioning technique can be used to within a few centimeters' precision at any rate by estimating
30-s satellite clock errors and interpolating them.
Received: 16 May 2000 / Accepted: 23 October 2000 相似文献
9.
In order to study the Baltic Sea Level change and to unify national height systems a two week GPS campaign was performed in the region in Autumn 1990. Parties from Denmark, Finland, Germany, Poland and Sweden carried out GPS measurements at 26 tide gauges along the Baltic sea and 8 VLBI and SLR fiducial stations with baseline lengths ranging from 230 km to 1600 km. The observations were processed in the network mode with the Bernese version 3.3 software using orbit improvement techniques. To get rid of the scale error introduced by the ionospheric refraction from single-frequency data, the local models of the ionosphere were estimated using L4 observations. The tropospheric zenith corrections were also considered. The preliminary results show average root mean square (RMS) errors of about ±3 cm in the horizontal position and ±7 cm in the vertical position relative to the Potsdam SLR station in ITRF89 system. After transformation of the GPS results to geoid heights using the levelled heights, an absolute comparison with gravimetric geoid heights using the least squares modification of Stokes' formula (LSMS), the modified Molodensky and the NKG Scandinavian geoid 1989 (NGK-89) models gives a standard deviation of the difference of ±7cm to ±9cm for the NKG-89 model and of ±9cm to ±30cm for the LSMS and the modified Molodensky model. The Swedish height system is found to be about 8-37cm higher than those of the other Baltic countries for NKG-89 model. 相似文献
10.
Accuracy of GPS-derived relative positions as a function of interstation distance and observing-session duration 总被引:6,自引:0,他引:6
Ten days of GPS data from 1998 were processed to determine how the accuracy of a derived three-dimensional relative position
vector between GPS antennas depends on the chord distance (denoted L) between these antennas and on the duration of the GPS observing session (denoted T). It was found that the dependence of accuracy on L is negligibly small when (a) using the `final' GPS satellite orbits disseminated by the International GPS Service, (b) fixing
integer ambiguities, (c) estimating appropriate neutral-atmosphere-delay parameters, (d) 26 km ≤ L ≤ 300 km, and (e) 4 h ≤T ≤ 24 h. Under these same conditions, the standard error for the relative position in the north–south dimension (denoted S
n
and expressed in mm) is adequately approximated by the equation S
n
=k
n
/T
0.5 with k
n
=9.5 ± 2.1 mm · h0.5 and T expressed in hours. Similarly, the standard errors for the relative position in the east–west and in the up-down dimensions
are adequately approximated by the equations S
e
=k
e
/T
0.5 and S
u
=k
u
/T
0.5, respectively, with k
e
=9.9 ± 3.1 mm · h0.5 and k
u
=36.5 ± 9.1 mm · h0.5.
Received: 5 February 2001 / Accepted: 14 May 2001 相似文献
11.
Considering a GPS satellite and two terrestrial stations, two types of equations are derived relating the heights of the
two stations to the measured data (frequency ratio or clock rate differences) and the coordinates and velocity components
of all three participating objects. The potential possibilities of using such relations for the determination of heights (in
terms of geopotential numbers or orthometric heights) are discussed.
Received: 6 December 2000 / Accepted: 9 July 2001 相似文献
12.
A methodology for precise determination of the fundamental geodetic parameter w
0, the potential value of the Gauss–Listing geoid, as well as its time derivative 0, is presented. The method is based on: (1) ellipsoidal harmonic expansion of the external gravitational field of the Earth
to degree/order 360/360 (130 321 coefficients; http://www.uni-stuttgard.de/gi/research/ index.html projects) with respect
to the International Reference Ellipsoid WGD2000, at the GPS positioned stations; and (2) ellipsoidal free-air gravity reduction
of degree/order 360/360, based on orthometric heights of the GPS-positioned stations. The method has been numerically tested
for the data of three GPS campaigns of the Baltic Sea Level project (epochs 1990.8,1993.4 and 1997.4). New w
0 and 0 values (w
0=62 636 855.75 ± 0.21 m2/s2, 0=−0.0099±0.00079 m2/s2 per year, w
0/&γmacr;=6 379 781.502 m,0/&γmacr;=1.0 mm/year, and &γmacr;= −9.81802523 m2/s2) for the test region (Baltic Sea) were obtained. As by-products of the main study, the following were also determined: (1)
the high-resolution sea surface topography map for the Baltic Sea; (2) the most accurate regional geoid amongst four different
regional Gauss–Listing geoids currently proposed for the Baltic Sea; and (3) the difference between the national height datums
of countries around the Baltic Sea.
Received: 14 August 2000 / Accepted: 19 June 2001 相似文献
13.
LIU Jiyu CHEN Xiaoming 《地球空间信息科学学报》2000,3(1):50-56
l lntroductionIn the winter Of l989 Wuhan Technical Universi-ty of Surveying and Mapping COntracted withTrimble Navigation Ltd. to purchase fOur TrimbIe4000SST receivers. They were required tO suit theaeriaI phWetric work without intreducing avelocity limitation. In February, l993 twO of thereceivers were uPgraded to provide two eventrnarker plugfords and one pulse Per second(lPPS) output axkets. The uPgradd receivers canincormrate external event markers, e. g. the shutter.oPening … 相似文献
14.
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
15.
Two long time series were analysed: the C01 series of the International Earth Rotation Service and the pole series obtained
by re-analysis of the classical astronomical observations using the HIPPARCOS reference frame. The linear drift of the pole
was determined to be 3.31 ± 0.05 milliarcseconds/year towards 76.1 ± 0.80° west longitude. For the least-squares fit the a priori correlations between simultaneous pole coordinates x
p
, y
p
were taken into account, and the weighting function was calculated by estimating empirical variance components. The decadal
variations of the pole path were investigated by Fourier and wavelet analysis. Using sliding windows, the periods and amplitudes
of the Chandler wobble and annual wobble were determined. Typical periods in the variable Chandler wobble and annual wobble
parameters were obtained from wavelet analyses.
Received: 21 January 2000 / Accepted: 28 August 2000 相似文献
16.
World Geodetic Datum 2000 总被引:7,自引:1,他引:6
Based on the current best estimates of fundamental geodetic parameters {W
0,GM,J
2,Ω} the form parameters of a Somigliana-Pizzetti level ellipsoid, namely the semi-major axis a and semi-minor axis b (or equivalently the linear eccentricity ) are computed and proposed as a new World Geodetic Datum 2000. There are six parameters namely the four fundamental geodetic
parameters {W
0,GM,J
2,Ω} and the two form parameters {a,b} or {a,ɛ}, which determine the ellipsoidal reference gravity field of Somigliana-Pizzetti type constraint to two nonlinear condition
equations. Their iterative solution leads to best estimates a=(6 378 136.572±0.053)m, b=(6 356 751.920 ± 0.052)m, ɛ=(521 853.580±0.013)m for the tide-free geoide of reference and a=(6 378 136.602±0.053)m, b=(6 356 751.860±0.052)m, ɛ=(521 854.674 ± 0.015)m for the zero-frequency tide geoid of reference. The best estimates of the
form parameters of a Somigliana-Pizzetti level ellipsoid, {a,b}, differ significantly by −0.39 m, −0.454 m, respectively, from the data of the Geodetic Reference System 1980.
Received: 1 February 1999 / Accepted: 31 August 1999 相似文献
17.
18.
为充分发挥GPS基准站的作用,使之灵活适应GPS差分和大地测量、地球动力学等多种需要,本文采用正交函数基底实时合成了所需指定采样率下的等效观测值,算法稳定可靠,可扩大GPS基准站的应用范围。 相似文献
19.
The New Hebrides experiment consisted of setting up a pair of DORIS beacons in remote tropical islands in the southwestern
Pacific, between 1993 and 1997. Because of orbitography requirements on TOPEX/Poséidon, the beacons were only transmitting
to SPOT satellites. Root-mean-square (RMS) scatters at the centimeter level on the latitude and vertical components were achieved,
but 2-cm RMS scatters affected the longitude component. Nevertheless, results of relative velocity (123 mm/year N250°) are
very consistent with those obtained using the global positioning system (GPS) (126 mm/yr N246°). The co-seismic step (12 mm
N60°) related to the Walpole event (M
W = 7.7) is consistent with that derived from GPS (10 mm N30°) or from the centroid moment tensor (CMT) of the quake (12 mm
N000°).
Received: 19 November 1999 / Accepted: 17 May 2000 相似文献
20.
P. Moore 《Journal of Geodesy》2001,75(5-6):241-254
Dual satellite crossovers (DXO) between the two European Remote Sensing satellites ERS-1 and ERS-2 and TOPEX/Poseidon are
used to (1) refine the Earth's gravity field and (2) extend the study of the ERS-2 altimetric range stability to cover the
first four years of its operation. The enhanced gravity field model, AGM-98, is validated by several methodologies and will
be shown to provide, in particular, low geographically correlated orbital error for ERS-2. For the ERS-2 altimetric range
study, TOPEX/Poseidon is first calibrated through comparison against in situ tide gauge data. A time series of the ERS-2 altimeter
bias has been recovered along with other geophysical correction terms using tables for bias jumps in the range measurements
at the single point target response (SPTR) events. On utilising the original version of the SPTR tables the overall bias drift
is seen to be 2.6±1.0 mm/yr with an RMS of fit of 12.2 mm but with discontinuities at the centimetre level at the SPTR events.
On utilising the recently released revised tables, SPTR2000, the drift is better defined at 2.4±0.6 mm/yr with the RMS of
fit reduced to 3.7 mm. Investigations identify the sea-state bias as a source of error with corrections affecting the overall
drift by close to 1.2 mm/yr.
Received: 25 May 2000 / Accepted: 24 January 2001 相似文献