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The use of geodetic techniques, in particular of the global positioning system (GPS), or other global navigation satellite systems (GNSS), for monitoring different kinds of deformations is a common practice. This is typically performed by setting a network of geodetic GPS/GNSS receivers, allowing accuracies in the order of millimeters. The use of lower-cost devices has been recently studied, showing that good results can be achieved. In this paper, the impact of the software used for the data analysis is also investigated to verify whether a fully low-cost monitoring system, i.e., both hardware and software, can be set up. This is done by performing a series of relative positioning experiments in which data are processed by different software packages. The main result is that by using a low-cost u-blox EVK-6T GPS receiver and analyzing its data with free and open-source software, movements of the order of a few millimeters can be detected when a short baseline with daily solutions is used. [ABSTRACT FROM AUTHOR]

NOAA’s National Geodetic Survey has developed the horizontal time-dependent positioning (HTDP) software to provide a way for its users to estimate the coordinate changes associated with horizontal crustal motion in the United States. HTDP contains a model for estimating horizontal crustal velocities and separate models for estimating the displacements associated with 29 earthquakes (two in Alaska and 27 in California). This software is updated periodically to provide more accurate estimates for crustal velocities and earthquake displacements, as well as to include models for additional earthquakes. In June 2008, NGS released version 3.0 of HTDP (HTDP 3.0) that introduces an improved capability for predicting crustal velocities, based on a tectonic block model of the western contiguous United States (CONUS), that is, from the Rockies to the Pacific coast. Values for the model parameters that predict the velocity at any point within the domain were estimated from 4,890 horizontal velocity vectors (derived from repeated geodetic observations), 170 fault slip rates, and 258 fault slip vector azimuths. Extensive testing indicates that this model can predict velocities within CONUS with a standard error of less than 2 mm/year in both the north and east components. HTDP 3.0 also introduces a model for the combined coseismic and postseismic displacements associated with the magnitude 7.9 Denali earthquake that occurred in central Alaska on November 3, 2002. [ABSTRACT FROM AUTHOR]

The observations of geodetic very long baseline interferometry (VLBI) measurements refer to an invariant point of the radio telescope. This point is often called the reference point. For the interpretation of VLBI results it is necessary to know the position of this invariant point and its possible variation with time. Only the knowledge of the reference point makes it possible to combine VLBI results with results from other colocated techniques and in the framework of the global geodetic observing system (GGOS). Within the GGOS an automated monitoring of the reference points and therefore of the local-tie vectors at colocation stations is discussed earlier in other studies. In this paper a new mathematical model is described to allow such an automated monitoring of the reference point of an azimuth-elevation type radio telescope. [ABSTRACT FROM AUTHOR]

The rapid and precise determination of the azimuth information, purely based on the satellite positioning technology of global positioning system (GPS), is tested and evaluated by this paper. The main consideration of using GPS for the azimuth determination is expected to replace the traditional astronomical azimuth measurement, which is believed to be time-consuming and weather-dependent. A GPS approach is simply based on setting up the GPS receivers at the two ends of a baseline, recording and processing the phase observable, and converting its coordinate solution into an azimuth with the inverse geodetic formulas. This type of azimuth obtained by the GPS static solution has been assessed to be well consistent with the astronomical azimuth by a level of better than ±1″. The GPS kinematic mode of azimuth value, however, is biased from the standard value for a RMS error of ±9″. The correction of the deflection of the vertical, theoretically required by the geodetic and astronomical azimuth conversion, is also implemented and found to be only effective at the observation site where the η tan φ value is higher than the estimation accuracy of the η value provided by a gravimetric geoid model. [ABSTRACT FROM AUTHOR]

Vincenty’s (1975) formulas for the direct and inverse geodetic problems (i.e., in relation to the geodesic) have been verified by comparing them with a new formula developed by adapting a fourth-order Runge-Kutta scheme for the numerical solution of ordinary differential equations, advancing the work presented by Kivioja in 1971. A total of 3,801 lines of varying distances (10 to 18,000 km) and azimuths (0 to 90°, because of symmetry) were used to compare these two very different techniques for computing geodesics. In every case, the geodesic distances agreed to within 0.115 mm, and the forward and reverse azimuths agreed to within 5×10-6 seconds of arc, thus verifying Vincenty’s formula. If one wishes to plot the trajectory of the geodesic, however, the fourth-order Runge-Kutta extension of Kivioja’s formula is recommended as a numerically efficient and convenient approach. [ABSTRACT FROM AUTHOR]