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51.
Error sources which decrease the accuracy of GPS in absolute velocity determination have been changed since SA was turned off. Firstly, quantities of all kinds of error sources that influence velocity determination are analyzed. The potential accuracy of GPS absolute velocity determination is derived from both theory and field GPS data simulation. After that, two tests were carried out to evaluate the performance of GPS absolute velocity determination in the case of a static and an airborne GPS receiver and INS (Inertial Navigation System) instrument in kinematic mode. In static mode, the receiver velocity has been estimated to be several mm/s with the carrier-phase derived Doppler measurements, and several cm/s with the receiver generated Doppler measurements. In kinematic mode, GPS absolute velocity estimates are compared with the synchronized measurements from the high accuracy INS. The root mean square statistics of the velocity discrepancies between GPS and INS come up to dm/s. Moreover, it has a strong correlation with the acceleration or jerk of the aircraft. 相似文献
52.
On the multivariate total least-squares approach to empirical coordinate transformations. Three algorithms 总被引:2,自引:1,他引:1
The multivariate total least-squares (MTLS) approach aims at estimating a matrix of parameters, Ξ, from a linear model (Y−E
Y
= (X−E
X
) · Ξ) that includes an observation matrix, Y, another observation matrix, X, and matrices of randomly distributed errors, E
Y
and E
X
. Two special cases of the MTLS approach include the standard multivariate least-squares approach where only the observation
matrix, Y, is perturbed by random errors and, on the other hand, the data least-squares approach where only the coefficient matrix
X is affected by random errors. In a previous contribution, the authors derived an iterative algorithm to solve the MTLS problem
by using the nonlinear Euler–Lagrange conditions. In this contribution, new lemmas are developed to analyze the iterative
algorithm, modify it, and compare it with a new ‘closed form’ solution that is based on the singular-value decomposition.
For an application, the total least-squares approach is used to estimate the affine transformation parameters that convert
cadastral data from the old to the new Israeli datum. Technical aspects of this approach, such as scaling the data and fixing
the columns in the coefficient matrix are investigated. This case study illuminates the issue of “symmetry” in the treatment
of two sets of coordinates for identical point fields, a topic that had already been emphasized by Teunissen (1989, Festschrift
to Torben Krarup, Geodetic Institute Bull no. 58, Copenhagen, Denmark, pp 335–342). The differences between the standard least-squares
and the TLS approach are analyzed in terms of the estimated variance component and a first-order approximation of the dispersion
matrix of the estimated parameters. 相似文献
53.
Modelling Positional Uncertainty of Line Features by Accounting for Stochastic Deviations from Straight Line Segments 总被引:1,自引:0,他引:1
Sytze de Bruin 《Transactions in GIS》2008,12(2):165-177
The assessment of positional uncertainty in line and area features is often based on uncertainty in the coordinates of their elementary vertices which are assumed to be connected by straight lines. Such an approach disregards uncertainty caused by sampling and approximation of a curvilinear feature by a sequence of straight line segments. In this article, a method is proposed that also allows for the latter type of uncertainty by modelling random rectangular deviations from the conventional straight line segments. Using the model on a dense network of sub‐vertices, the contribution of uncertainty due to approximation is emphasised; the sampling effect can be assessed by applying it on a small set of randomly inserted sub‐vertices. A case study demonstrates a feasible way of parameterisation based on assumptions of joint normal distributions for positional errors of the vertices and the rectangular deviations and a uniform distribution of missed sub‐vertices along line segments. Depending on the magnitudes of the different sources of uncertainty, not accounting for potential deviations from straight line segments may drastically underestimate the positional uncertainty of line features. 相似文献
54.
55.
对工程测量学的地位和应用领域,通用和专用仪器的发展,在理论和实践上进行了归纳和总结。简要地叙述了工程测量在国内外的发展情况及其发展趋势。 相似文献
56.
Craig W. Morgan Graham M. Kent Gordon G. Seitz Michaela Novak 《Hydrogeology Journal》2008,16(5):981-994
A hydrogeologic model that has been used by many researchers and consultants to describe an area of South Lake Tahoe, California,
USA impacted by MTBE contamination describes a relatively homogeneous unconfined aquifer comprised of poorly sorted glacial
outwash deposits, within which water-supply wells are able to exert significant alteration in natural groundwater flow. A
re-examination of the area’s hydrogeology is presented, which supports a layered heterogeneous aquifer system constructed
of alternating fine and coarser-grained glacio-lacustrine depositional units. This re-evaluation was accomplished through
a review of lithologic logs across an area of approximately 1 km2, combined with observations of significant hydraulic head differences and knowledge of the depositional environments controlled
by Pleistocene Lake Tahoe high stands. Many of the fine-grained units observed at depths from 6 to 15 m, although relatively
thin, are generally continuous and serve as significant barriers to groundwater flow. The vertical migration of contamination
across these fine-grained units to deeper groundwaters was facilitated by cross-screened monitoring wells installed as part
of site investigation activities. This conclusion highlights the importance of geologic characterization and proper monitoring
well construction at contaminated site investigations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Michaela NovakEmail: |
57.
In this paper, we formulate a finite-element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation
model of poroelasticity. We approximate the flow variables by a mixed finite-element space and the displacement by a family
of discontinuous Galerkin methods. Theoretical convergence error estimates are derived and, in particular, are shown to be
independent of the constrained specific storage coefficient, c
o
. This suggests that our proposed algorithm is a potentially effective way to combat locking, or the nonphysical pressure
oscillations, which sometimes arise in numerical algorithms for poroelasticity. 相似文献
58.
An updated analysis of geothermal data from the highland area of eastern Brazil has been carried out and the characteristics of regional variations in geothermal gradients and heat flow examined. The database employed includes results of geothermal measurements at 45 localities. The results indicate that the Salvador craton and the adjacent metamorphic fold belts northeastern parts of the study area are characterized by geothermal gradients in the range of 6–17°C/km. The estimated heat flow values fall in the range of 28–53 mW/m2, with low values in the cratonic area relative to the fold belts. On the other hand, the São Francisco craton and the intracratonic São Francisco sedimentary basin in the southwestern parts are characterized by relatively higher gradient values, in the range of 14–42°C/km, with the corresponding heat flow values falling in the range of 36–89 mW/m2. Maps of regional variations indicate that high heat flow anomaly in the São Francisco craton is limited to areas of sedimentary cover, to the west of the Espinhaço mountain belt. Crustal thermal models have been developed to examine the implications of the observed intracratonic variations in heat flow. The thermal models take into consideration variation of thermal conductivity with temperature as well as change of radiogenic heat generation with depth. Vertical distributions of seismic velocities were used in obtaining estimates of radiogenic heat production in crustal layers. Crustal temperatures are calculated based on a procedure that makes simultaneous use of the Kirchoff and Generalized Integral Transforms, providing thereby analytical solutions in 2D and 3D geometry. The results point to temperature variations of up to 300°C at the Moho depth, between the northern Salvador and southern São Francisco cratons. There are indications that differences in rheological properties, related to thermal field, are responsible for the contrasting styles of deformation patterns in the adjacent metamorphic fold belts. 相似文献
59.
Comparison of numerical models of two debris flows in the Cortina d’ Ampezzo area,Dolomites, Italy 总被引:2,自引:0,他引:2
The accurate prediction of runout distances, velocities and the knowledge of flow rheology can reduce the casualties and property
damage produced by debris flows, providing a means to delineate hazard areas, to estimate hazard intensities for input into
risk studies and to provide parameters for the design of protective measures. The application of most of models that describe
the propagation and deposition of debris flow requires detailed topography, rheological and hydrological data that are not
always available for the debris-flow hazard delineation and estimation. In the Cortina d’Ampezzo area, Eastern Dolomites,
Italy, most of the slope instabilities are represented by debris flows; 325 debris-flow prone watersheds have been mapped
in the geomorphological hazard map of this area. We compared the results of simulations of two well-documented debris flows
in the Cortina d’Ampezzo area, carried on with two different single-phase, non-Newtonian models, the one-dimensional DAN-W
and the two-dimensional FLO-2D, to test the possibility to simulate the dynamic behaviour of a debris flow with a model using
a limited range of input parameters. FLO-2D model creates a more accurate representation of the hazard area in terms of flooded
area, but the results in terms of runout distances and deposits thickness are similar to DAN-W results. Using DAN-W, the most
appropriate rheology to describe the debris-flow behaviour is the Voellmy model. When detailed topographical, rheological
and hydrological data are not available, DAN-W, which requires less detailed data, is a valuable tool to predict debris-flow
hazard. Parameters obtained through back-analysis with both models can be applied to predict hazard in other areas characterized
by similar geology, morphology and climate. 相似文献
60.