共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
The secular latitude variations of the five ILS stations of Mizusawa, Kitab, Carloforte, Gaithersburg and Ukiah were analyzed
taking into account the recent continental drift theory. Using Le Pichon's 1968 reconstruction, the rate of rotation was computed
from the astronomical data, fixing the pole of rotation by Le Pichon's determination. The most reasonable solution was obtained
considering Mizusawa, Kitab and Carloforte lying on the Eurasia plate, the two American stations as one on the American plate
(Gaithersburg) and the other on the North—East Pacific plate (Ukiah). The resulting relative rate between the Euro-American
plates is found to be 0".0028/year and between the American—Pacific plates 0".0032/ years, or about 1°,3/106 years and in excellent agreement with the plate tectonic theory.
Luxembourg Meeting of the “Journées Luxembourgeoises de Géodynamique”, 1972. 相似文献
3.
LIQi CAOJian 《地球空间信息科学学报》2004,7(2):101-103
This paper is to construct a “digital local, regional, region“ information framework based on the technology of “SIG“ and its significance and application to the regional sustainable development evaluation system. First, the concept of the “grid computing“ and “SIG“ is interpreted and discussed, then the relationship between the “grid computing“ and “digital region“ is analyzed, and the framework of the “digital region“ is put forward. Finally, the significance and application of “grid computing“ to the “region sustainable development evaluation system“ are discussed. 相似文献
4.
M. I. Yurkina 《Journal of Geodesy》1985,59(2):150-166
Summary Huygens undoubtedly used the notion of the potential in his well-known work “Discours de la cause de la pesanteur” (Leyden,
1690), investigating the Earth's figure by means of Newton's famous canals. Maupertuis used this notion in a similar work
published in London in 1733. The notion of potential was used by Clairaut in the “Théorie de la figure de la Terre” (Paris,
1743) and by D'Alembert in many articles (1752, 1761, 1768, 1773, 1780). Euler used it also in many of his works since 1736.
These examples of application of the potential were not noticed because of peculiarities of terminology.
相似文献
5.
The upward-downward continuation of a harmonic function like the gravitational potential is conventionally based on the direct-inverse
Abel-Poisson integral with respect to a sphere of reference. Here we aim at an error estimation of the “planar approximation”
of the Abel-Poisson kernel, which is often used due to its convolution form. Such a convolution form is a prerequisite to
applying fast Fourier transformation techniques. By means of an oblique azimuthal map projection / projection onto the local
tangent plane at an evaluation point of the reference sphere of type “equiareal” we arrive at a rigorous transformation of
the Abel-Poisson kernel/Abel-Poisson integral in a convolution form. As soon as we expand the “equiareal” Abel-Poisson kernel/Abel-Poisson
integral we gain the “planar approximation”. The differences between the exact Abel-Poisson kernel of type “equiareal” and
the “planar approximation” are plotted and tabulated. Six configurations are studied in detail in order to document the error
budget, which varies from 0.1% for points at a spherical height H=10km above the terrestrial reference sphere up to 98% for points at a spherical height H = 6.3×106km.
Received: 18 March 1997 / Accepted: 19 January 1998 相似文献
6.
By minimizing the global distance between the (quasi-) geoid and an ellipsoid of revolution, the best parameters of an ellipsoid
and its location parameters are estimated. Input data are the absolute value of the geopotential at (quasi-) geoid level,
a set of harmonic coefficients from satellite, terrestrial or combined observations, the mean rotational speed of the earth,
and approximate values of the seminajor axis and the eccentricity of the ellipsoid. The output ranges from 6378137,63 m and
6378141,62 m for the best semimajor axis and from 298.259758 and 298.259651 for the reciprocal value of the best ellipsoidal
flattening within WD 1 and WD 2. The best translational parameters are 6.4 cm (Greenwich-direction), 0.8 cm (orthogonal to
Greenwich-direction), and 1.9 cm (parallel to rotational axis of the earth); the best rotational parameters are −0.2” (around
Greenwich-direction) and 1.1” (around orthogonal to Greenwich-direction). The dependence of the datum of the (quasi-) geoid
geopotential is studied in detail. 相似文献
7.
GNSS data management and processing with the GPSTk 总被引:2,自引:0,他引:2
Dagoberto Salazar Manuel Hernandez-Pajares Jose M. Juan Jaume Sanz 《GPS Solutions》2010,14(3):293-299
We organize complex problems in simple ways using a GNSS data management strategy based on “GNSS Data Structures” (GDS), coupled
with the open source “GPS Toolkit” (GPSTk) suite. The code resulting from using the GDS and their associated “processing paradigm”
is remarkably compact and easy to follow, yielding better code maintainability. Furthermore, the data abstraction allows flexible
handling of concepts beyond mere data encapsulation, including programmable general solvers. An existing GPSTk class can be
modified to achieve the goal. We briefly describe the “GDS paradigm” and show how the different GNSS data processing “objects”
may be combined in a flexible way to develop data processing strategies such as Precise Point Positioning (PPP) and network-based
PPP that computes satellite clock offsets on-the-fly. 相似文献
8.
The conventional international origin (CIO), established from observations made a century ago, is not directly related to observations by modern space-geodetic techniques. Both the greater precision of these techniques and improved knowledge of the structure of the Earth justify the need for a new CIO. We analyze recent polar motion time-series (VLBI, SLR, and GPS) to test estimators that might be used to establish such a new conventional origin. This new origin would be defined as the barycenter of the motion of the pole for a specific epoch. Consistency among the series examined is of the order of 2 milli-arc-seconds. A drift model can be employed in the analysis of specific series to establish an origin as the barycenter at a specific epoch, rather than the midpoint of the series. As an example, we estimate a “Conventional International Reference Origin” for the year 2000.0, using polar motion series that began in 1984. 相似文献
9.
E. W. Grafarend 《Journal of Geodesy》1981,55(4):286-299
WhenH. Moritz (1967, 1971) studied “kinematical geodesy” for the purpose of separation of gravitation and inertia, especially within combined
accelerometer-gradiometer systems, it was hard to believe that within five years time inertial survey systems would be available,
exactly operating according to his theoretical design. Here, we attempt to give a geodetic introduction into the fundamental
equation of inertial positioning materialized by inertial survey systems with emphasis on a careful error model, including
36 parameters of type time interval, initial positions, initial gravity, varying acceleration, varying gravity gradients,
accelerometer bias, accelerometer random uncertainty, accelerometer non-orthogonality, initial misalignment angles, accelerometer
scale factor uncertainty. The notion of “multipoint” boundary value problem and initial value problem of inertial positioning
is reviwed. So-called “post-mission” adjustment techniques for inertial surveys are discussed.
Presented at the 2nd International Symposium on Inertial Technology for Surveying and Geodesy, Banff, Canada, June 1–5, 1981. 相似文献
Sommaire QuandH. Moritz (1967, 1971) a étudié la géodésie cinématique dans le but de séparer la gravitation et l’inertie, spécialement en combinant accéléromètres et gradiomètres, il était difficile de croire qu’en cinq ans les systèmes d’arpentage inertiels seraient disponibles et fonctionneraient exactement selon ses prévisions théoriques. Ici, nous allons tenter de donner une introduction géodésique à l’équation fondamentale du positionnement inertiel, matérialisée par un système d’arpentage inertiel en soulignant l’importance d’un modèle d’erreur incluant 36 paramètres du genre intervalle de temps, positions initiales, gravité initiale, accélération variable, gradient de la gravité variable, déviation des accéléromètres, incertitude aléatoire des accéléromètres, non-orthogonalité des accéléromètres, angles initiaux des défauts d’alignement, incertitude du facteur d’échelle des accéléromètres. La notion de problème “multipoint” aux limites et du problème de la valeur initiale du positionnement inertiel y est revue. Les techniques de compensation “après la mission” y sont discutées.
Presented at the 2nd International Symposium on Inertial Technology for Surveying and Geodesy, Banff, Canada, June 1–5, 1981. 相似文献
10.
C. C. Tscherning 《Journal of Geodesy》1978,52(1):85-92
The term “entity” covers, when used in the field of electronic data processing, the meaning of words like “thing”, “being”,
“event”, or “concept”. Each entity is characterized by a set of properties.
An information element is a triple consisting of an entity, a property and the value of a property. Geodetic information is
sets of information elements with entities being related to geodesy. This information may be stored in the form ofdata and is called ageodetic data base provided (1) it contains or may contain all data necessary for the operations of a particular geodetic organization, (2)
the data is stored in a form suited for many different applications and (3) that unnecessary duplications of data have been
avoided.
The first step to be taken when establishing a geodetic data base is described, namely the definition of the basic entities
of the data base (such as trigonometric stations, astronomical stations, gravity stations, geodetic reference-system parameters,
etc...).
Presented at the “International Symposium on Optimization of Design and Computation of Control Networks”, Sopron, Hungary,
July 1977. 相似文献
11.
A. Sakuma 《Journal of Geodesy》1963,37(3):249-260
Résumé L'état actuel des études préliminaires d'une mesure absolue de g au B.I.P.M. basée sur le principe de la “méthode des deux
stations” [1] est résumé dans cette note.
Une précision de g plus élevée que celle qui a été obtenue jusqu'à présent, est espérée à cause des avantages des mesures
symétriques dans cette méthode et des observations interférentielles des passages d'un corps lancé (un trièdre formé de trois
miroirs orthogonaux) à des stations fixes.
Nous envisageons qu'une précision de g de l'ordre de 0,1 mgal sera réalisable avec cette méthode.
Summary In this note, the present stage is outlined in the preparations for an absolute determination of gravity at B.I.P.M., based on the principle of “La méthode des deux stations” [1] (or so called “The up and down motion method”). It is expected that a value of g of greater accuracy than previous measurements will be obtained, due to the use of the symmetrical measurements by this principle and the use of the interferometric observations of the passage of the projected body (a corner cube reflector) in free fall across fixed horizontal stations. It seems probable that an accuracy of the order of 0.1 mgal will be obtained by this method.相似文献
12.
József Ádám 《Journal of Geodesy》1982,56(3):180-195
The Euclidean spaces with their inner products are used to describe methods of least squares adjustment as orthogonal projections
on finite-dimensional subspaces. A unified Euclidean space approach to the least squares adjustment methods “observation equations”
and “condition equations” is suggested. Hence not only the two adjustment solutions are treated from the view-point of Euclidean
space theory in a unified frame but also the existing duality relation between the methods of “observation equations” and
“condition equations” is discussed in full detail. Another purpose of this paper is to contribute to the development of some
familiarity with Euclidean and Hilbert space concepts. We are convinced that Euclidean and Hilbert space techniques in least
squares adjustment are elegant and powerful geodetic methods. 相似文献
13.
Due to the super rotation of the Earth's inner core, the tilted figure axis of the inner core would progress with respect to the mantle and thus cause the variation of the Earth's external gravity field. This paper improves the present model of the gravity field variation caused by the inner core super rotation. Under the assumption that the inner core is a stratifying ellipsoid whose density function is fitted out from PREM and the super rotation rate is 0.27-0.53°/yr, calculations show that the global temporal variations on the Earth's surface have a maximum value of about 0.79-1.54×10^3 pGal and a global average intensity of about 0.45-0.89×10^ 3 μGal in the whole year of 2007, which is beyond the accuracy of the present gravimetry and even the super conducting gravimeter data. However, both the gravity variations at Beijing and Wuhan vary like sine variables with maximal variations around 0.33 pGal and 0.29 pGal, respectively, in one cycle. Thus, continuous gravity measurements for one or two decades might be able to detect the differential motion of the inner core. 相似文献
14.
Selectivity estimation is crucial for query optimizers choosing an optimal spatial execution plan in a spatial database management system.This paper presents an Annular Bucket spatial histogram(AB histogram)that can estimate the selectivity in finer spatial selection and spatial join operations even when the spatial query has more operators or more joins.The AB histogram is represented as a set of bucket-range,bucket-count value pairs.The bucket-range often covers an annular region like a sin-gle-cell-sized photo frame.The bucket-count is the number of objects whose Minimum Bounding Rectangles(MBRs)fall between outer rectangle and inner rectangle of the bucket-range.Assuming that all MBRs in each a bucket distribute evenly,for every buck-et,we can obtain serial probabilities that satisfy a certain spatial selection or join conditions from the operations’ semantics and the spatial relations between every bucket-range and query ranges.Thus,according to some probability theories,spatial selection or join selectivity can be estimated by the every bucket-count and its probabilities.This paper also shows a way to generate an updated AB histogram from an original AB histogram and those probabilities.Our tests show that the AB histogram not only supports the selectivity estimation of spatial selection or spatial join with "disjoint","intersect","within","contains",and "overlap" operators but also provides an approach to generate a reliable updated histogram whose spatial distribution is close to the distribution of ac-tual query result. 相似文献
15.
J. A. Weightman 《Journal of Geodesy》1967,41(3):237-247
Summary A datum change between two geodetic systems with points in common may be derived in three stages; slight adjustments of coordinates
to make the networks of common points geometrically similar in the two systems; a scale factor to make them geometrically
congruent; finally, an orthogonal transformation to swing them into coincidence.
The geometrical concept is developed of a “datum screw”, not arbitrarily chosen as is the “origin” or “datum point” of a geodetic
survey, but intrinsic to the geometry. The conditions under which it degenerates to a simple “datum shift” are discussed.
Differential and other formulae for changes of spheroid and of datum are given, together with a set of tables of coefficients. 相似文献
16.
We compare two methods for monitoring the dynamic response of tall buildings to wind loading, using data from a 280-m-high
building in Singapore. The first method is based on accelerometer measurements. The second method is based on the Global Positioning
System (GPS) technology. The GPS can in principle detect absolute displacements with lower frequencies than the accelerometers,
but the GPS positioning signal is usually very noisy. We propose a systematic procedure for modeling the stochastic and systematic
components of the GPS displacement time series and for extracting the weak structural response from the dominant noise. The
spectrum of the building response obtained from the filtered GPS data exhibits a dominant peak at 0.19 Hz. The frequency of
the peak coincides with that obtained from the analysis of the accelerometer data. The proposed analysis of the GPS signal
provides a method for cross-validating the GPS and accelerometer measurements, and shows that “educated” filtering of the
GPS signal can reveal essential features of the building’s response to wind loading. 相似文献
17.
Sommaire La discussion des observations des latitudes faites dans des stations astronomiques situées sur les continents divers peut
permettre de déterminer des mouvements des continents.
L'accroissement du nombre des stations astronomiques permet de déceler non seulement le déplacement des continents mais aussi
des mouvements de rotation des continents.
Le travail qui. suit a été présenté au Symposium tenu à Zurich en septembre 1974 et consacré aux “Problems of Recent Crustal
Movements”. N. Stoyko est revenu gravement malade de ce symposium (il devait décéder deux ans plus tard) sans avoir pu contribuer
à la rédaction de cette communication qui ainsi ne se trouve pas insérée dans les actes du Symposium de Zurich.
A. Stoyko a rédigé le texte par la suite et j'ai demandé au Bulletin Géodésique en hommage à N. Stoyko s'il pouvait en assurer
la publication. Je le remercie d'avoir bien voulu le faire.S. Débarbat
“Problems of Recent Crustal Movements”, Fourth International Symposium, Moscow, USSR, 1971 Ed. “Valgus”, Tallinn, 1975, pp.
205–211. 相似文献
18.
Arcsecond-level accuracy of NASA's ICESat (Ice, Cloud, and land Elevation Satellite) satellite laser altimeter beam pointing
angle is required to satisfy the scientific goal of detecting centimeter-level elevation changes, over time, in the Greenland
and Antarctic ice sheets. Two different approaches, termed “topographic inferred” and “direct detection”, were examined for
calibrating the laser pointing angle (that is, detecting and removing pointing determination bias) at the 1.5-arcsec level,
using information independent of the onboard pointing instrumentation. Both approaches entail estimating the beam pointing
by differencing the three-dimensional position of the altimeter instrument and the laser-beam spot (or “footprint”) location
on the ground. Analytical assessments of the two approaches are discussed, along with recommendations for the ICESat pointing
determination calibration strategy.
Received: 28 April 2000 / Accepted: 6 November 2000 相似文献
19.
The spacetime gravitational field of a deformable body 总被引:3,自引:0,他引:3
The high-resolution analysis of orbit perturbations of terrestrial artificial satellites has documented that the eigengravitation
of a massive body like the Earth changes in time, namely with periodic and aperiodic constituents. For the space-time variation
of the gravitational field the action of internal and external volume as well as surface forces on a deformable massive body
are responsible. Free of any assumption on the symmetry of the constitution of the deformable body we review the incremental
spatial (“Eulerian”) and material (“Lagrangean”) gravitational field equations, in particular the source terms (two constituents:
the divergence of the displacement field as well as the projection of the displacement field onto the gradient of the reference
mass density function) and the `jump conditions' at the boundary surface of the body as well as at internal interfaces both
in linear approximation. A spherical harmonic expansion in terms of multipoles of the incremental Eulerian gravitational potential
is presented. Three types of spherical multipoles are identified, namely the dilatation multipoles, the transport displacement
multipoles and those multipoles which are generated by mass condensation onto the boundary reference surface or internal interfaces.
The degree-one term has been identified as non-zero, thus as a “dipole moment” being responsible for the varying position
of the deformable body's mass centre. Finally, for those deformable bodies which enjoy a spherically symmetric constitution,
emphasis is on the functional relation between Green functions, namely between Fourier-/ Laplace-transformed volume versus
surface Love-Shida functions (h(r),l(r) versus h
′(r),l
′(r)) and Love functions k(r) versus k
′(r). The functional relation is numerically tested for an active tidal force/potential and an active loading force/potential,
proving an excellent agreement with experimental results.
Received: December 1995 / Accepted: 1 February 1997 相似文献
20.
Generalization of total least-squares on example of unweighted and weighted 2D similarity transformation 总被引:5,自引:2,他引:3
Frank Neitzel 《Journal of Geodesy》2010,84(12):751-762
In this contribution it is shown that the so-called “total least-squares estimate” (TLS) within an errors-in-variables (EIV)
model can be identified as a special case of the method of least-squares within the nonlinear Gauss–Helmert model. In contrast
to the EIV-model, the nonlinear GH-model does not impose any restrictions on the form of functional relationship between the
quantities involved in the model. Even more complex EIV-models, which require specific approaches like “generalized total
least-squares” (GTLS) or “structured total least-squares” (STLS), can be treated as nonlinear GH-models without any serious
problems. The example of a similarity transformation of planar coordinates shows that the “total least-squares solution” can
be obtained easily from a rigorous evaluation of the Gauss–Helmert model. In contrast to weighted TLS, weights can then be
introduced without further limitations. Using two numerical examples taken from the literature, these solutions are compared
with those obtained from certain specialized TLS approaches. 相似文献