共查询到20条相似文献，搜索用时 78 毫秒
1.
Ephemeris errors of GPS satellites 总被引：2，自引：0，他引：2
Oscar L. Colombo 《Journal of Geodesy》1986,60(1):64-84
Ephemeris errors are supposed to be a major factor limiting the usefulness ofGPS in high precision geodesy. Considerations of orbital mechanics suggest that, regardless of their complexity, the uncertainties
in the solar radiation pressure model, the gravity field model, and the estimated initial state, may have simple effects on
the ephemeris. This possibility has been tested by fitting linear combinations of simple functions—chosen on theoretical grounds—to
simulated errors of three-day ephemerides. With a set of five functions for the across-track component, six for the radial,
and seven for the along-track, it has been possible to fit the position errors to better than 1% of theirr.m.s values, in all the caces studied. The simulations included —besides solar radiation pressure errors—gravity field model and
initial state uncertainties, as well as an unknown constant force along the axis of the solar panels. The solar radiation
force was calculated taking into account the shape, orientation, and physical properties (reflectivity and specularity) of
the main parts of the spacecraft, under various conditions of illumination (continuous sunlight, eclipses, etc.). 相似文献
2.
Decorrelated GRACE time-variable gravity solutions by GFZ,and their validation using a hydrological model 总被引：14，自引：6，他引：8
We have analyzed recent gravity recovery and climate experiment (GRACE) RL04 monthly gravity solutions, using a new decorrelating
post-processing approach. We find very good agreement with mass anomalies derived from a global hydrological model. The post-processed
GRACE solutions exhibit only little amplitude damping and an almost negligible phase shift and period distortion for relevant
hydrological basins. Furthermore, these post-processed GRACE solutions have been inspected in terms of data fit with respect
to the original inter-satellite ranging and to SLR and GPS observations. This kind of comparison is new. We find variations
of the data fit due to solution post-processing only within very narrow limits. This confirms our suspicion that GRACE data
do not firmly ‘pinpoint’ the standard unconstrained solutions. Regarding the original Kusche (J Geod 81:733–749, 2007) decorrelation
and smoothing method, a simplified (order-convolution) approach has been developed. This simplified approach allows to realize
a higher resolution—as necessary, e.g., for generating computed GRACE observations—and needs far less coefficients to be stored. 相似文献
3.
Existing methods for gross error detection, based on the mean shift model or the variance inflation model, have hardly considered
or taken advantage of the potential prior information on the unknown parameters. This paper puts forward a Bayesian approach
for gross error detection when prior information on the unknown parameters is available. Firstly, based on the basic principle
of Bayesian statistical inference, the Bayesian method—posterior probability method—for the detection of gross errors is established.
Secondly, considering either non-informative priors or normal-gamma priors on the unknown parameters, the computational formula
of the posterior probability is given for both the mean shift model and the variance inflation model, respectively, under
the condition of unequal weight and independent observations. Finally, as an example, a triangulation network is computed
and analyzed, which shows that the method given here is feasible. 相似文献
4.
Dan Sharni 《Journal of Geodesy》1973,47(3):309-312
Is the intense controversy between French and English scientists of the late 1600 th and early 1700 th—relating to the figure
of the Earth—reflected in the “most obstinate war” fought between “the two great empires of Lilliput and Blefuscu”—over the
correct way of breaking eggs? 相似文献
5.
Erik W. Grafarend 《Journal of Geodesy》1985,59(2):124-138
Summary From a two-dimensional network adjustment it is well understood that the one orientation unknown of a theodolite frame is
estimable, once the orientation datum parameter, e.g., one azimuth, is fixed. In three-dimensional networks the problem of
estimability of three orientation unknowns inherent in a theodolite frame is more complex. Here we prove that not only the
classical horizontal orientation unknown is estimable (up to the datum degrees of freedom), but also astronomical longitude
and astronomical latitude which can be considered as two additional orientation unknowns of the theodolite frame moving with
respect to an earth-fixed equatorial frame of reference. Thus the theodolite instrument can be considered—at least theoretically—a
gradiometer measuring the variation of the directional parameters of the gravity vector from one point to another. Or up to
the datum degrees of freedom astronomical longitude and astronomical latitude can be determined from only theodolite observations
between exclusively terrestrial points. M?nicke (1982), has shown that despite the refraction problem the method works sufficiently
well in practice. 相似文献
6.
Aniela Makowska 《Journal of Geodesy》1969,43(1):17-22
Summary The paper contains an analysis of the character and the quantity of variations of vertical angles, and an analysis of dependences
of those variations upon meteorological elements, made on the basis of results of observations carried out at four points
in the Polish Tatra Mountains (Figure 1).
The analyses comprise four measurement periods: July 1963, June 1964, October 1964 and May 1965.
The observations of the vertical angles and of the meteorological factors had been made simultaneously at three points. The
meteorological findings have been complemented by data obtained from the mountain meteorological stations.
The analysis of results reveals a fairly good consistency between the refraction variations and the changes in the mean temperature
gradients for observations from the mountain peaks and for the sight lines with a quite great distance from the ground—provided
a steady weather permits for observations of the zenith distance to be made during several days. 相似文献
7.
GPS slant total electron content accuracy using the single layer model under different geomagnetic regions and ionospheric conditions 总被引：8，自引：3，他引：5
The use of observations from the Global Positioning System (GPS) has significantly impacted the study of the ionosphere. As
it is widely known, dual-frequency GPS observations can provide very precise estimation of the slant Total Electron Content
(sTEC—the linear integral of the electron density along a ray-path) and that the precision level is bounded by the carrier-phase
noise and multi-path effects on both frequencies. Despite its precision, GPS sTEC estimations can be systematically affected
by errors in the estimation of the satellites and receivers by Inter-Frequency Biases (IFB) that are simultaneously determined
with the sTEC. Thus, the ultimate accuracy of the GPS sTEC estimation is determined by the errors with which the IFBs are
estimated. This contribution attempts to assess the accuracy of IFBs estimation techniques based on the single layer model
for different ionospheric regions (low, mid and high magnetic latitude); different seasons (summer and winter solstices and
spring and autumn equinoxes); different solar activity levels (high and low); and different geomagnetic conditions (quiet
and very disturbed). The followed strategy relies upon the generation of a synthetic data set free of IFB, multi-path, measurement
noise and of any other error source. Therefore, when a data set with such properties is used as the input of the IFB estimation
algorithms, any deviation from zero on the estimated IFBs should be taken as indications of the errors introduced by the estimation
technique. The truthfulness of this assessment work is warranted by the fact that the synthetic data sets resemble, as realistically
as possible, the different conditions that may happen in the real ionosphere. The results of this work show that during the
high solar activity period the accuracy for the estimated sTEC is approximately of ±10 TECu for the low geomagnetic region
and of ±2.2 TECu for the mid-latitude. During low solar activity the accuracy can be assumed to be in the order of ±2 TECu.
For the geomagnetic high-disturbed period, the results show that the accuracy is degraded for those stations located over
the region where the storm has the strongest impact, but for those stations over regions where the storm has a moderate effect,
the accuracy is comparable to that obtained in the quiet period. 相似文献
8.
Since the beginning of the International Global Navigation Satellite System (GLONASS) Experiment, IGEX, in October 1998,
the Center for Orbit Determination in Europe (CODE) has acted as an analysis center providing precise GLONASS orbits on a
regular basis. In CODE's IGEX routine analysis the Global Positioning System (GPS) orbits and Earth rotation parameters are
introduced as known quantities into the GLONASS processing. A new approach is studied, where data from the IGEX network are
combined with GPS observations from the International GPS Service (IGS) network and all parameters (GPS and GLONASS orbits,
Earth rotation parameters, and site coordinates) are estimated in one processing step. The influence of different solar radiation
pressure parameterizations on the GLONASS orbits is studied using different parameter subsets of the extended CODE orbit model.
Parameterization with three constant terms in the three orthogonal directions, D, Y, and X (D = direction satellite–Sun, Y = direction of the satellite's solar panel axis), and two periodic terms in the X-direction, proves to be adequate for GLONASS satellites. As a result of the processing it is found that the solar radiation
pressure effect for the GLONASS satellites is significantly different in the Y-direction from that for the GPS satellites, and an extensive analysis is carried out to investigate the effect in detail.
SLR observations from the ILRS network are used as an independent check on the quality of the GLONASS orbital solutions. Both
processing aspects, combining the two networks and changing the orbit parameterization, significantly improve the quality
of the determined GLONASS orbits compared to the orbits stemming from CODE's IGEX routine processing.
Received: 10 May 2000 / Accepted: 9 October 2000 相似文献
9.
10.
Kamil Eren 《Journal of Geodesy》1984,58(2):137-150
In earthquake prediction studies geodetic surveys play a very significant role. For this purpose, in Turkey, three micro geodetic
networks have been established across the North Anatolian Fault. Of these, the Ismetpa§a Network is the subject of this paper.
From the observations in combined triangulation—trilateration mode in 1972 and 1982 the horizontal movements and strain components
were determined. Afterwards the parameters of the best fitting deformation model were computed and analyzed. The results show
that the Anatolian plate has about a 1 cm/year westward motion, and there exists considerable strain accumulation in the area. 相似文献
11.
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
12.
W. S. B. Paterson 《Journal of Geodesy》1955,29(4):42-54
Values of the refraction coefficient, calculated from simultaneous reciprocal vertical angles measured on a traverse across
North Greenland, and meteorological observations made at the same time are analysed statistically. A relation is established
between diurnal changes in refraction and changes in air temperature. Values of the refraction coefficient are also correlated
with wind speed, amount of cloud, and presence of drifting snow near the surface. No correlation is found between refraction
and atmospheric pressure over the range of pressures encountered. A regression equation is given for estimating refraction
from observed meteorological conditions. Direct measurements of temperature gradient in the air layers near the surface are
compared with gradients deduced from the refraction observations.
Zusammenfassung Der Inhalt der vorliegenden Arbeit ist eine statistische Analyse der Schwankungen des Refraktionskoeffizienten in Gr?nland und seiner Korrelationen mit den meteorologischen Beobachtungen, also mit der Temperatur, der Windgeschwindigkeit, der Dunstbildung und des Flugschnees. Ferner werden Vergleiche der Temperaturgradienten angestellt, die sich einerseits aus direkten Messungen, andererseits aus den Refraktions-messungen ergeben.
Resumen El articulo presenta un análisis estadístico de las variaciones del coeficiente de refracción en Groenlandia y de sus correlaciones con las observaciones meteorológicas—temperatura, velocidad del viento, nubosidad, viento de nieve. Se comparan igualmente los gradientes de la temperatura, tales como resultan de medidas directas y de las medidas de la refracción.
Résumé L’article présente une analyse statistique des variations du coefficient de réfraction au Groenland et de ses correlations avec les observations météorologiques—température, vitesse du vent, nébulosité, vent de neige. On compare également les gradients de la température, tels qu’ils résultent de mesures directes et des mesures de la réfraction.
Riassunto L’articolo presenta un analisi statistica delle variazioni del coefficiente di rifrazione in Groenlandia e delle correlazioni con le osservazioni meteorologiche: temperatura, velocità del vento, nebulosità, vento di neve. Vi compaiono anche i gradienti della temperatura come essi risultano da misure dirette e da misure della rifrazione.相似文献
13.
The separation between the reference surfaces for orthometric heights and normal heights—the geoid and the quasigeoid—is typically
in the order of a few decimeters but can reach nearly 3 m in extreme cases. The knowledge of the geoid–quasigeoid separation
with centimeter accuracy or better, is essential for the realization of national and international height reference frames,
and for precision height determination in geodetic engineering. The largest contribution to the geoid–quasigeoid separation
is due to the distribution of topographic masses. We develop a compact formulation for the rigorous treatment of topographic
masses and apply it to determine the geoid–quasigeoid separation for two test areas in the Alps with very rough topography,
using a very fine grid resolution of 100 m. The magnitude of the geoid–quasigeoid separation and its accuracy, its slopes,
roughness, and correlation with height are analyzed. Results show that rigorous treatment of topographic masses leads to a
rather small geoid–quasigeoid separation—only 30 cm at the highest summit—while results based on approximations are often
larger by several decimeters. The accuracy of the topographic contribution to the geoid–quasigeoid separation is estimated
to be 2–3 cm for areas with extreme topography. Analysis of roughness of the geoid–quasigeoid separation shows that a resolution
of the modeling grid of 200 m or less is required to achieve these accuracies. Gravity and the vertical gravity gradient inside
of topographic masses and the mean gravity along the plumbline are modeled which are important intermediate quantities for
the determination of the geoid–quasigeoid separation. We conclude that a consistent determination of the geoid and quasigeoid
height reference surfaces within an accuracy of few centimeters is feasible even for areas with extreme topography, and that
the concepts of orthometric height and normal height can be consistently realized and used within this level of accuracy. 相似文献
14.
A. M. C. Srivastava 《Journal of Geodesy》1984,58(4):510-517
The astrogeodetic—gravimetric method based on the principle of least—squares solution has been used to determine the geocentric
Indian geodetic datum making use of the available nongeocentric astrogeodetic data and the gravimetric geocentric geoidal
heights in the form of smoothened values. Everett's method of interpolation has been used to obtain the smoothened geoidal
heights at the astrogeodetic stations in India from the available generalized values at 1°×1° corners. The values of the geoidal
height and deflections of the vertical at the geodetic datum Kalianpur H.S. so obtained have the negligible difference from
the values computed earlier by the same method using directly computed gravimetric geoidal heights at the astrogeodetic stations,
indicating that the use of the interpolated values in the astrogeodetic—gravimetric method employed would be an economical
approach of absolute orientation of a nongeocentric system if the gravimetric geoidal heights are available at 1°×1° corners
in the area of interest. 相似文献
15.
Pramod Kumar Singh Sanjay Das S. R. Mohapatra 《Journal of the Indian Society of Remote Sensing》2012,40(1):85-96
The 2001 Bhuj earthquake (Mw 7.7), one of the most severe earthquakes in the recent history of India, reactivated various existing active faults. It is
manifested in the form of coseismic ground fissures/cracks and upheaval of land in the form of bumps. Identification and reactivation
of Loriya Fault is established by 1—Geomorphic changes with the help of digital imagery (LISS III images). 2—Coseismic changes
through ground checks and 3—Geophysical signatures through magnetic and gravity survey. A lineament cutting the north-western
part of the Pur River alluvial fan has been revealed by satellite imagery. The streams flowing along the lineament add to
the evidences of a weak plane, while the occurrence of coseismic ground fissures confirms the existence of an active fault.
No dip slip movement is recorded in the trenches made across the Loriya active fault while the en-echelon pattern of ground
fissures suggest strike slip movement along the fault due to 2001 earthquake. 相似文献
16.
Sarvesh Palria Akanksha Singh J. R. Sharma Suparn Pathak 《Journal of the Indian Society of Remote Sensing》2005,33(2):259-266
The Keoladeo National Park, Bharatpur, a man-made fresh water wetland carved out of a natural depression on the floodplain
of two minor tributaries of the Yamuna-Gambhir and the Banganga is the country’s finest waterfowl habitat. This important
wetland was set aside as a bird sanctuary in 1956 and it was elevated to the status of a National Park in 1981. It was also
designated a Ramsar site- a wetland of international importance under the Ramsar convention. This important wetland has distinction
of being the only Indian wetland to be included under both the Ramsar and the World Heritage convention.
The attempt has been made to evaluate the habitat of Sarus crane in the Keoladeo National Park using satellite data — IRS
LISS III and PAN merged product and GIS. Geocoded data of IRS —1C LISS III of 21 March 1999 on 1: 50,000 scale and PAN data
of March 17, 1999 were used to generate the vegetation cover type map and open water. The maps showing drainage, human habitations,
contours, roads, etc. were prepared using the Survey of India topographical sheets and contour map of park area. Information
regarding habitat parameters was collected from the existing literature and field observations. The Sarus crane mainly fed
in the wetland on the rhizome ofNymphaea sp.,Scirpus tuberosus andEleocharis plantaginea. As there were changes in their habitat requirements at different seasons, the sighting of Sarus crane in each habitat were
recorded along with the time and activity during observation. The most utilized habitat for the entire period of study was
moderately wet grassland followed by pools. The pools were used mainly during the summer. The water depth requirement observed
was between 30–40 cm and 20–40 cm. The suitability maps for Sarus crane were then generated using all remote sensing based
and conventional information using rule based equations in the GIS within the Keoladeo National Park. 相似文献
17.
The general inertial positioning problem—to determine the actual coordinates of a vehicle, moving with respect to the inertial
frame, from its measured inertial accelerations—is discussed in Hamiltonian mechanics. The use of the Hamiltonian formalism
allows the avoidance of sophisticated geometrical considerations.
Starting from the canonical equations of motion for the general problem, the navigation equations of some special problems
(motion on a rotating sphere, motion on a rotating ellipsoid) are derived in linearized form. Using the simplicity of the
linearized form, the solutions can be easily computed in analytical form. This is done for the above problems. 相似文献
18.
ABSTRACTThe Moon, Earth’s only natural satellite, is a potential new platform for Earth observation. Moreover, with the wide applicability of the angular information from remote sensing data, it has been attracting increasingly more attention. Accordingly, this study focuses on the angular characteristics of Moon-based Earth observations. Using ephemeris DE430 and Earth orientation parameters, the position and attitude of the Sun, Earth, and Moon were obtained and their coordinates normalized to a single framework using coordinate transformations between the related reference systems. Then, an angular geometric model of Moon-based Earth observations was constructed, and the corresponding angular algorithms were presented. The results revealed the angular range and distribution characteristics of Moon-based Earth observations. For every point on the surface of the Earth, the view and solar zenith angles all vary widely, which decreases with increasing latitude. The view and solar zenith angles all vary widely with the largest range of values in the equatorial and polar regions and a smaller range of values in mid-latitudes. Furthermore, the range of solar angles of Moon-based Earth observations is the same as that of all-time solar angles, indicating the potential for monitoring and understanding large-scale geoscientific phenomena using Moon-based Earth observations. 相似文献
19.
The efficacy of robust M-estimators is a well-known issue when dealing with observational blunders. When the number of observations
is considerably large—long time series for instance—one can take advantage of the asymptotic normality of the M-estimation
and compute reasonable estimates for the unknown parameters of interest. A few leading M-estimators have been employed to
identify the most likely functional model for GPS coordinate time series. This includes the simultaneous detection of periodic
patterns and offsets in the GPS time series. Estimates of white noise, flicker noise, and random walk noise components are
also achieved using the robust M-estimators of (co)variance components, developed in the framework of the least-squares variance
component estimation (LS-VCE) theory. The method allows one to compute confidence interval for the (co)variance components
in asymptotic sense. Simulated time series using white noise plus flicker noise show that the estimates of random walk noise
fluctuate more than those of flicker noise for different M-estimators. This is because random walk noise is not an appropriate
noise structure for the series. The same phenomenon is observed using the results of real GPS time series, which implies that
the combination of white plus flicker noise is well described for GPS time series. Some of the estimated noise components
of LS-VCE differ significantly from those of other M- estimators. This reveals that there are a large number of outliers in
the series. This conclusion is also affirmed by performing the statistical tests, which detect (large) parts of the outliers
but can also leave parts to be undetected. 相似文献
20.
G. Beutler W. Gurtner M. Rothacher T. Schildknecht I. Bauersima 《Journal of Geodesy》1986,60(3):205-220
Summary Carrier phase measurements are potentially the most precise observations available from theGPS satellite system, the formal precision being of the order of one centimeter per observation. If the so called double differences
are used as the basic observable, the analysis is relatively simple, since satellite- and receiver-clocks may be represented
by basic models. We investigate the feasibility of double difference phase observations for orbit determination using the
material of the 1985 High Precision Baseline Test, where the coordinates of the so called fiducial points (Haystack, Ft. Davis
Richmond and Mojave) are held fixed.TI-4100 andAFGL-receiver observations were used in the same orbit determination process.
Although no surface weather data had been available to us, the orbit quality seems to be of the order of0.1 ppm. When we use these orbits to estimate the coordinates of the five “non-fiducial points” Owens Valley, Hat Creek Mammoth Lake,
Austin and Dahlgren we get a repeatability of the order of5 cm for latitude and longitude and10 cm for height, if the observations of the first four days of the campaign are compared to those of the second four days.
If we use our orbits estimated withTI andAFGL observations to process the Mojave—Owens Valley baseline (length245 km) measured by the twoSERIES-X receivers, we obtain day to day repeatabilities of1.6 cm (0.06 ppm) in length,2 cm (0.08 ppm) in latitude,4 cm (0.16 ppm) in longitude and7 cm (0.29 ppm) in height.
Since there are indications that regional networks will be realized in the near future, the results presented here should
encourage the realization of regional high precision orbit determination services. 相似文献