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1.
Cheinway Hwang Tzu-Pang Tseng Tingjung Lin Dražen Švehla Bill Schreiner 《Journal of Geodesy》2009,83(5):477-489
The joint Taiwan–US mission FORMOSAT-3/ COSMIC (COSMIC) was launched on April 17, 2006. Each of the six satellites is equipped
with two POD antennas. The orbits of the six satellites are determined from GPS data using zero-difference carrier-phase measurements
by the reduced dynamic and kinematic methods. The effects of satellite center of mass (COM) variation, satellite attitude,
GPS antenna phase center variation (PCV), and cable delay difference on the COSMIC orbit determination are studied. Nominal
attitudes estimated from satellite state vectors deliver a better orbit accuracy when compared to observed attitude. Numerical
tests show that the COSMIC COM must be precisely calibrated in order not to corrupt orbit determination. Based on the analyses
of the 5 and 6-h orbit overlaps of two 30-h arcs, orbit accuracies from the reduced dynamic and kinematic solutions are nearly
identical and are at the 2–3 cm level. The mean RMS difference between the orbits from this paper and those from UCAR (near
real-time) and WHU (post-processed) is about 10 cm, which is largely due to different uses of GPS ephemerides, high-rate GPS
clocks and force models. The kinematic orbits of COSMIC are expected to be used for recovery of temporal variations in the
gravity field. 相似文献
2.
Local geoid determination combining gravity disturbances and GPS/levelling: a case study in the Lake Nasser area, Aswan, Egypt 总被引:1,自引:0,他引:1
C. C. Tscherning Awar Radwan A. A. Tealeb S. M. Mahmoud M. Abd El-Monum Ramdan Hassan I. El-Syaed K. Saker 《Journal of Geodesy》2001,75(7-8):343-348
The use of GPS for height control in an area with existing levelling data requires the determination of a local geoid and
the bias between the local levelling datum and the one implicitly defined when computing the local geoid. If only scarse gravity
data are available, the heights of new data may be collected rapidly by determining the ellipsoidal height by GPS and not
using orthometric heights. Hence the geoid determination has to be based on gravity disturbances contingently combined with
gravity anomalies. Furthermore, existing GPS/levelling data may also be used in the geoid determination if a suitable general
gravity field modelling method (such as least-squares collocation, LSC) is applied. A comparison has been made in the Aswan
Dam area between geoids determined using fast Fourier transform (FFT) with gravity disturbances exclusively and LSC using
only the gravity disturbances and the disturbances combined with GPS/levelling data. The EGM96 spherical harmonic model was
in all cases used in a remove–restore mode. A total of 198 gravity disturbances spaced approximately 3 km apart were used,
as well as 35 GPS/levelling points in the vicinity and on the Aswan Dam. No data on the Nasser Lake were available. This gave
difficulties when using FFT, which requires the use of gridded data. When using exclusively the gravity disturbances, the
agreement between the GPS/levelling data were 0.71 ± 0.17 m for FFT and 0.63 ± 0.15 for LSC. When combining gravity disturbances
and GPS/levelling, the LSC error estimate was ±0.10 m. In the latter case two bias parameters had to be introduced to account
for a possible levelling datum difference between the levelling on the dam and that on the adjacent roads.
Received: 14 August 2000 / Accepted: 28 February 2001 相似文献
3.
Tzu-Pang Tseng Kefei Zhang Cheinway Hwang Urs Hugentobler Chuan-Sheng Wang Suelynn Choy Yi-Shan Li 《GPS Solutions》2014,18(2):219-230
We provide suggestions for the approved COSMIC-2 satellite mission regarding the field of view (FOV) and the clock stability of its future GNSS receiver based on numerical analyses using COSMIC GPS data. While the GRACE GPS receiver is mounted on the zenith direction, the precise orbit determination (POD) antennas of COSMIC are not. The COSMIC antenna design results in a narrow FOV and a reduction in the number of GPS observations. To strengthen the GPS geometry, GPS data from two POD antennas of COSMIC are used to estimate its orbits. The phase residuals of COSMIC are at the centimeter level, compared to the millimeter level of GRACE. The receiver clock corrections of COSMIC and GRACE are at the microsecond and nanosecond levels, respectively. The clock spectra of COSMIC at the frequencies of 0–0.005 Hz contain significant powers, indicating potential systematic errors in its clock corrections. The clock stability, expressed by the Allan deviation, of COSMIC ranges from 10?9 to 10?11 over 1 to 104 s, compared to 10?12 to 10?14 for GRACE. Compared to USO-based clock of GRACE, the clock of COSMIC is degraded in its stability and is linked to the reduction of GPS data quality. Lessons for improvement of COSMIC-2 over COSMIC in FOV and receiver clock stability are given. 相似文献
4.
This study evaluates the quality of GPS radio occultation (RO) atmospheric excess phase data derived with single- and double-difference
processing algorithms. A spectral analysis of 1 s GPS clock estimates indicates that a sampling interval of 1 s is necessary
to adequately remove the GPS clock error with single-difference processing. One week (May 2–8, 2009) of COSMIC/FORMOSAT-3
data are analyzed in a post-processed mode with four different processing strategies: (1) double-differencing with 1 s GPS
ground data, (2) single-differencing with 30 s GPS clock estimates (standard COSMIC Data Analysis and Archival Center product),
(3) single-differencing with 5 s GPS clocks, and (4) single-differencing with 1 s GPS clocks. Analyses of a common set of
5,596 RO profiles show that the neutral atmospheric bending angles and refractivities derived from single-difference processing
with 1 s GPS clocks are the highest quality. The random noise of neutral atmospheric bending angles between 60 and 80 km heights
is about 1.50e−6 rad for the single-difference cases and 1.74e−6 rad for double-differencing. An analysis of pairs of collocated
soundings also shows that bending angles derived from single-differencing with 1 s GPS clocks are more consistent than with
the other processing strategies. Additionally, the standard deviation of the differences between RO and high-resolution European
Center for Medium range Weather Forecasting (ECMWF) refractivity profiles at 30 km height is 0.60% for single-differencing
with 1 and 5 s GPS clocks, 0.68% for single-differencing with 30 s clocks, and 0.66% for double-differencing. A GPS clock-sampling
interval of 1 s or less is required for single- and zero-difference processing to achieve the highest quality excess atmospheric
phase data for RO applications. 相似文献
5.
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
6.
A new approach for airborne vector gravimetry using GPS/INS 总被引:2,自引:2,他引:2
A new method for airborne vector gravimetry using GPS/INS has been developed and the results are presented. The new algorithm
uses kinematic accelerations as updates instead of positions or velocities, and all calculations are performed in the inertial
frame. Therefore, it is conceptually simpler, easier, more straightforward and computationally less expensive compared to
the traditional approach in which the complex navigation equations should be integrated. Moreover, it is a unified approach
for determining all three vector components, and no stochastic gravity modeling is required. This approach is based on analyzing
the residuals from the Kalman filter of sensor errors, and further processing with wavenumber coefficient filterings is applied
in case closely parallel tracks of data are available. An application to actual test-flight data is performed to test the
validity of the new algorithm. The results yield an accuracy in the down component of about 3–4 mGal. Also, comparable results
are obtained for the horizontal components with accuracies of about 6 mGal. The gravity modeling issue is discussed and alternative
methods are presented, none of which improves on the original approach.
Received: 18 April 2000 / Accepted: 14 August 2000 相似文献
7.
W. E. Featherstone J. F. Kirby A. H. W. Kearsley J. R. Gilliland G. M. Johnston J. Steed R. Forsberg M. G. Sideris 《Journal of Geodesy》2001,75(5-6):313-330
The AUSGeoid98 gravimetric geoid model of Australia has been computed using data from the EGM96 global geopotential model,
the 1996 release of the Australian gravity database, a nationwide digital elevation model, and satellite altimeter-derived
marine gravity anomalies. The geoid heights are on a 2 by 2 arc-minute grid with respect to the GRS80 ellipsoid, and residual
geoid heights were computed using the 1-D fast Fourier transform technique. This has been adapted to include a deterministically
modified kernel over a spherical cap of limited spatial extent in the generalised Stokes scheme. Comparisons of AUSGeoid98
with GPS and Australian Height Datum (AHD) heights across the continent give an RMS agreement of ±0.364 m, although this apparently
large value is attributed partly to distortions in the AHD.
Received: 10 March 2000 / Accepted: 21 February 2001 相似文献
8.
A study of the impact of FORMOSAT-3/COSMIC GPS radio occultation (RO) and dropwindsonde data on regional model simulations
for a 11-day period during the 2007 Mei-yu season is presented. The Weather Research and Forecasting (WRF) model and its three-dimensional
variation component, WRF-Var, are used for regional model predictions of heavy rainfall events in Taiwan. Without the use
of GPS RO and dropwindsonde data, pressure and relative humidity are, in general, underestimated by the model; temperature
predictions have a warm bias at the low level and a cold bias at the high level; and the east–west and north–south component
winds have positive and negative biases, respectively. Incorporating GPS RO data tends to improve the prediction for longer
integration. The assimilation of dropwindsonde data improves the forecast at the earlier time and at higher levels, and the
improvement decreases over time. The reason the dropwindsonde data produce a positive impact earlier and the GPS RO data later
is that there are few GPS RO observations in the fine domain. The large-scale simulation is first improved using the GPS RO
observations, and the resulting changes can have a positive impact on the mesoscale at the later time. The dropwindsonde observations
were taken inside the fine domain such that their impact can be detected early in the simulation. With both types of observation
included, the prediction shows even greater improvement. At the earlier forecast time, there is nearly no impact from GPS
and dropwindsonde data on rainfall forecasts. However, at the later integration time, the GPS data start to significantly
improve the rainfall forecast. The dropwindsonde data also provide a positive impact on rainfall forecasts, but it is not
as significant as that of the GPS data. 相似文献
9.
GPS-based precise orbit determination of the very low Earth-orbiting gravity mission GOCE 总被引:5,自引:0,他引:5
A prerequisite for the success of future gravity missions like the European Gravity field and steady-state Ocean Circulation
Explorer (GOCE) is a precise orbit determination (POD). A detailed simulation study has been carried out to assess the achievable
orbit accuracy based on satellite-to-satellite tracking (SST) by the US global positioning system (GPS) and in conjunction
the implications for gravity field determination. An orbit accuracy at the few centimeter level seems possible, sufficient
to support the GOCE gravity mission and in particular its gravity gradiometer.
Received: 21 January 2000 / Accepted: 4 July 2000 相似文献
10.
本文介绍了从单一温度廓线提取重力波的水平波长、垂直波长、势能和动量通量的方法,利用2007~2008年COSMIC干温廓线数据计算得到了可以表征中尺度重力波活动特征的相关参数值在各年夏季和冬季的全球分布。结果与国内外已有的相关结果在形态分布上符合较好。结果表明,在20~30 km大气层,重力波在北半球处于冬季时的活动明显强于夏季,重力波的活动呈现纬向分布特征,夏半球高纬地区的重力波活动有明显的季节性变化,重力波的活动主要受地形和对流作用影响。COSMIC数据计算的动量通量分布大致与势能分布趋于一致。 相似文献
11.
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
12.
GPS-assisted GLONASS orbit determination 总被引:1,自引:0,他引:1
D. Kuang Y. E. Bar-Sever W. I. Bertiger K. J. Hurst J. F. Zumberge 《Journal of Geodesy》2001,75(11):569-574
Using 1 week of data from a network of GPS/GLONASS dual-tracking receivers, 15-cm accurate GLONASS orbit determination is
demonstrated with an approach that combines GPS and GLONASS data. GPS data are used to define the reference frame, synchronize
receiver clocks and determine troposphere delay for the GLONASS tracking network. GLONASS tracking data are then processed
separately, with the GPS-defined parameters held fixed, to determine the GLONASS orbit. The quality of the GLONASS orbit determination
is currently limited by the size and distribution of the tracking network, and by the unavailability of a sufficiently refined
solar pressure model. Temporal variations in the differential clock bias of the dual-tracking receivers are found to have
secondary impact on the orbit determination accuracy.
Received: 5 January 2000 / Accepted: 15 February 2001 相似文献
13.
A data-driven approach to local gravity field modelling using spherical radial basis functions 总被引:3,自引:0,他引:3
We propose a methodology for local gravity field modelling from gravity data using spherical radial basis functions. The methodology
comprises two steps: in step 1, gravity data (gravity anomalies and/or gravity disturbances) are used to estimate the disturbing
potential using least-squares techniques. The latter is represented as a linear combination of spherical radial basis functions
(SRBFs). A data-adaptive strategy is used to select the optimal number, location, and depths of the SRBFs using generalized
cross validation. Variance component estimation is used to determine the optimal regularization parameter and to properly
weight the different data sets. In the second step, the gravimetric height anomalies are combined with observed differences
between global positioning system (GPS) ellipsoidal heights and normal heights. The data combination is written as the solution
of a Cauchy boundary-value problem for the Laplace equation. This allows removal of the non-uniqueness of the problem of local
gravity field modelling from terrestrial gravity data. At the same time, existing systematic distortions in the gravimetric
and geometric height anomalies are also absorbed into the combination. The approach is used to compute a height reference
surface for the Netherlands. The solution is compared with NLGEO2004, the official Dutch height reference surface, which has
been computed using the same data but a Stokes-based approach with kernel modification and a geometric six-parameter “corrector
surface” to fit the gravimetric solution to the GPS-levelling points. A direct comparison of both height reference surfaces
shows an RMS difference of 0.6 cm; the maximum difference is 2.1 cm. A test at independent GPS-levelling control points, confirms
that our solution is in no way inferior to NLGEO2004. 相似文献
14.
Y. M. Wang 《Journal of Geodesy》1999,73(1):29-34
The formulas of the ellipsoidal corrections to the gravity anomalies computed using the inverse Stokes integral are derived.
The corrections are given in the integral formulas and expanded in the spherical harmonics series. If a coefficient model
such as the OSU91A is given, the corrections can be easily computed.
Received: 19 August 1996 / Accepted: 28 September 1998 相似文献
15.
M. S. Senobari 《Journal of Geodesy》2010,84(5):277-291
A method for airborne vector gravimetry has been developed. The method is based on developing the error dynamics equations
of the INS in the inertial frame where the INS system errors are estimated in a wave estimator using inertial GPS position
as update. Then using the error-corrected INS acceleration and the GPS acceleration in the inertial frame, the gravity disturbance
vector is extracted. In the paper, the focus is on the improvement of accuracy for the horizontal components of the airborne
gravity vector. This is achieved by using a decoupled model in the wave estimator and decorrelating the gravity disturbance
from the INS system errors through the estimation process. The results of this method on the real strapdown INS/DGPS data
are promising. The internal accuracy of the horizontal components of the estimated gravity disturbance for repeated airborne
lines is comparable with the accuracy of the down component and is about 4–8 mGal. Better accuracy (2–4 mGal) is achieved
after applying a wave-number correlation filter (WCF) to the parallel lines of the estimated airborne gravity disturbances. 相似文献
16.
Cheinway Hwang Tzu-Pang Tseng Ting-Jung Lin Dražen Švehla Urs Hugentobler Benjamin Fong Chao 《GPS Solutions》2010,14(1):121-131
The precise orbit determination antennas of F3/C and GRACE-A satellites are from the same manufacturer, but are installed
in different configurations. The current orbit accuracy of F3/C is 3 cm at arcs with good GPS data, compared to 1 cm of GRACE,
which has a larger ratio of usable GPS data. This paper compares the qualities of GPS observables from F3/C and GRACE. Using
selected satellites and time spans, the following average values for the satellite F3/C and satellite A of GRACE are obtained:
multipath effect on the pseudorange P1, 0.78 and 0.38 m; multipath effect on the pseudorange P2, 1.03 and 0.69 m; occurrence
frequency of cycle slip, 1/29 and 1/84; standard error of unit weight, 4 and 1 cm; dynamic–kinematic orbit difference, 10
and 2 cm. For gravity determination using F3/C GPS data, a careful selection of GPS data is critical. With six satellites
in orbit, F3/C’s large amount of GPS data will make up the deficiency in data quality. 相似文献
17.
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
18.
Two numerical techniques are used in recent regional high-frequency geoid computations in Canada: discrete numerical integration
and fast Fourier transform. These two techniques have been tested for their numerical accuracy using a synthetic gravity field.
The synthetic field was generated by artificially extending the EGM96 spherical harmonic coefficients to degree 2160, which
is commensurate with the regular 5′ geographical grid used in Canada. This field was used to generate self-consistent sets of synthetic gravity anomalies and
synthetic geoid heights with different degree variance spectra, which were used as control on the numerical geoid computation
techniques. Both the discrete integration and the fast Fourier transform were applied within a 6∘ spherical cap centered at each computation point. The effect of the gravity data outside the spherical cap was computed using
the spheroidal Molodenskij approach. Comparisons of these geoid solutions with the synthetic geoid heights over western Canada
indicate that the high-frequency geoid can be computed with an accuracy of approximately 1 cm using the modified Stokes technique,
with discrete numerical integration giving a slightly, though not significantly, better result than fast Fourier transform.
Received: 2 November 1999 / Accepted: 11 July 2000 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 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