47 research outputs found
The treatment of time continuous GPS observations for the determination of regional deformation parameters
No full textThe calculation of invariant deformation parame-ters, entering in the constitutional equations of crustal dynamics, requires information on the ge-ometry of the crust in the study region, which is continuous in both the time and spatial domain. The use of continuously observing GPS stations pro-vides geodetic data which are practically time-continuous and must be only spatially interpolated. A strategy is developed for the treatment of dense series of horizontal coordinates from a regional GPS network, which are typically exhibiting a time-linear behavior. The role of the choice of reference system is examined for the removal of trend before the spatial interpolation as well as the determination of the motion of the region as whole with respect to the ITRF or of the relative motion of tectonically homogeneous sub regions. Rigorous formulas are presented for various horizontal deformation pa-rameters and their intrinsic time derivatives, without the usual infinitesimal approximations. Finally the problem of quality assessment for the derived pa-rameters is investigated completely ignoring the questionable formal statistical characteristic of the original geodetic data. A realistic numerical exam-ple demonstrates the suggested techniques, involv-ing spatial interpolation by the classical finite-element method. A software package in standard C language has been developed in order to implement the proposed algorithms
On the feasibility to integrate low-cost MEMS accelerometers and GNSS receivers
No full textThe aim of this research was to investigate the feasibility of merging the benefits offered by low-cost GNSS and MEMS accelerometers technology, in order to promote the diffusion of low-cost monitoring solutions. A merging approach was set up at the level of the combination of kinematic results (velocities and displacements) coming from the two kinds of sensors, whose observations were separately processed, following to the so called loose integration, which sounds much more simple and flexible thinking about the possibility of an easy change of the combined sensors. At first, the issues related to the difference in reference systems, time systems and measurement rate and epochs for the two sensors were faced with. An approach was designed and tested to transform into unique reference and time systems the outcomes from GPS and MEMS and to interpolate the usually (much) more dense MEMS observation to common (GPS) epochs. The proposed approach was limited to time-independent (constant) orientation of the MEMS reference system with respect to the GPS one. Then, a data fusion approach based on the use of Discrete Fourier Transform and cubic splines interpolation was proposed both for velocities and displacements: MEMS and GPS derived solutions are firstly separated by a rectangular filter in spectral domain, and secondly back-transformed and combined through a cubic spline interpolation. Accuracies around 5 mm for slow and fast displacements and better than 2 mm/s for velocities were assessed. The obtained solution paves the way to a powerful and appealing use of low-cost single frequency GNSS receivers and MEMS accelerometers for structural and ground monitoring applications. Some additional remarks and prospects for future investigations complete the paper
Probabilistic and deterministic aspects of linear estimation in geodesy
No full textRecent advances in observational techniques related to geodetic work (VLBI, laser ranging) make it imperative that more consideration should be given to modeling problems. Uncertainties in the effect of atmospheric refraction, polar motion and precession-nutation parameters, cannot be dispensed with in the context of centimeter level geodesy. Even physical processes that have generally been previously altogether neglected (station motions) must now be taken into consideration. The problem of modeling functions of time or space, or at least their values at observation points (epochs) is explored. When the nature of the function to be modeled is unknown. The need to include a limited number of terms and to a priori decide upon a specific form may result in a representation which fails to sufficiently approximate the unknown function. An alternative approach of increasing application is the modeling of unknown functions as stochastic processes
A model of plate motion
No full textThe wide use of space geodesy techniques devoted to geophysical and geodynamical purposes has recently evidenced some limitations due to the intrinsic Terrestrial Reference Frame (TRF) definition. Current TRFs are defined under hypotheses suited to overcome the rank deficiency of the observations with respect to the parameters that have to be estimated, i.e. coordinates and velocities (Dermanis, 2001; Dermanis, 2002).
From a geodetic point of view, one possibility implies the application of the no-net-rotation condition (NNR). One of the main geophysical consequences due to the application of this condition is that it allows only accurate estimations of relative motions, whilst other motions of geodynamical interest, for instance with respect to the inner layers of the Earth body, are not determinable.
The main purpose of this paper is to propose a unified way to describe plate motions, overcoming the problems introduced by the NNR condition, in order to establish a new reference frame useful for geodynamical applications too.
Since we believe relevant the role played by global tectonics inferences, we introduce the concept of the main tectonic sinusoid to propose an analytical description of the plate motions flow, which is polarized to the “west” in the hotspot reference frame.Published200-208ope
Design of experiment for earth rotation and baseline parameter determination from very long baseline interferometry
No full textThe possibility of recovering earth rotation and network geometry (baseline) parameters are emphasized. The numerical simulated experiments performed are set up in an environment where station coordinates vary with respect to inertial space according to a simulated earth rotation model similar to the actual but unknown rotation of the earth. The basic technique of VLBI and its mathematical model are presented. The parametrization of earth rotation chosen is described and the resulting model is linearized. A simple analysis of the geometry of the observations leads to some useful hints on achieving maximum sensitivity of the observations with respect to the parameters considered. The basic philosophy for the simulation of data and their analysis through standard least squares adjustment techniques is presented. A number of characteristic network designs based on present and candidate station locations are chosen. The results of the simulations for each design are presented together with a summary of the conclusions
Contribution of Apollo lunar photography to the establishment of selenodetic control
No full textAmong the various types of available data relevant to the establishment of geometric control on the moon, the only one covering significant portions of the lunar surface (20%) with sufficient information content, is lunar photography, taken at the proximity of the moon from lunar orbiters. The idea of free geodetic networks is introduced as a tool for the statistical comparison of the geometric aspects of the various data used. Methods were developed for the updating of the statistics of observations and the a priori parameter estimates to obtain statistically consistent solutions by means of the optimum relative weighting concept
