Open Access Published by De Gruyter Open Access

Volume 4 Issue 1

April 2014

Issue of Journal of Geodetic Science

Contents
Journal Overview

Open Access February 27, 2014

Comparison of Site Velocities Derived from Collocated GPS, VLBI and SLR Techniques at The Hartebeesthoek Radio Astronomy Observatory (Comparison of Site Velocities)

C. Munghemezulu, L. Combrinck, D. Mayer, O.J. Botai

More Download PDF

Abstract

Space geodetic techniques provide highly accurate methods for estimating bedrock stability at subcentimetre level. We utilize data derived from Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI) and Global Positioning Systems (GPS) techniques, collocated at the Hartebeesthoek Radio Astronomy Observatory, to characterise local plate motion and compare the solutions from the three techniques. Data from the GNSS station were processed using the GAMIT/GLOBK (version 10.4) software, data from the SLR station (MOBLAS-6)were processed using the Satellite Laser Ranging Data Analysis Software (SDAS) and the VLBI data sets were processed using the Vienna VLBI Software (VieVS) software. Results show that there is a good agreement between horizontal and vertical velocity components with a maximum deviation of 1.7 mm/yr, 0.7 mm/yr and 1.3 mm/yr between the North, East and Up velocity components respectively for the different techniques. At HartRAO there is no significant trend in the vertical component and all the techniques used are consistent with the a-priori velocities when compared with each other. This information is crucial in monitoring the local motion variations since geodetic instruments require a very stable base to minimise measurement errors. These findings demonstrate that station coordinate time-series derived with different techniques and analysis strategies provide comparable results.

Open Access March 6, 2014

Sensitivity of Goce Gradients on Greenland Mass Variation And Changes in Ice Topography

M. Herceg, C. C. Tscherning, J. F. Levinsen

More Download PDF

Abstract

The Gravity field and steady state Ocean Circulation Explorer (GOCE) maps variations in the gravity field by observing second order derivatives (gradients) of the Earth gravitational potential. Flying in the low altitude of 255 km and having a spatially dense data distribution of short wavelengths of the gravity field, GOCE may be used to enhance the time varying gravity signal coming fromthe GRACE satellites. The GOCE gradients may potentially be used for the determination of residual masses in local regions. This can be done using Least-Squares Collocation (LSC) or the Reduced Point Mass (RPM) method. In this study, different gravity field solutions are calculated by the use of RPM, LSC and GOCE gradients, respectively. Gravity field time series are created and presented for the six consecutive months of GOCE gradient observations, data being acquired between November 2009 and June 2010. Corresponding gravity anomaly results are used for the calculation of ice mass changes by the use of theRPMmethod. The results are then compared with the computed topographic effect of the ice by the use of a modified topographic correction and the Gravsoft TC program. The maximal gravity changes at the ground predicted from GOCE gradients are between 2 and 4 mGal for the period considered. The gravity anomaly estimation error arising from the GOCE gradient data using only T zz with an associated error of 20 mE is 11 mGal. This analysis shows the potential of using GOCE data for observations of ice mass changes although the GOCE dataset is limited to only six months. We expect four years of GOCE gradient observations to be available by mid-2014. This will increase the accuracy and spatial resolution of the GOCE measurements, which may lead to an accuracy necessary for observing ice mass changes.

Open Access March 11, 2014

Effect of La Niña on The Global Mean Sea Level And North Pacifc Ocean Mass Over 2005-2011

Habib B. Dieng, Anny Cazenave, Benoit Meyssignac, Olivier Henry, Karina von Schuckmann, Hindumathi Palanisamy, Jean Michel Lemoine

More Download PDF

Abstract

Interannual fluctuations of the global mean sea level are highly correlated with El Niño-Southern Oscillation (ENSO) events, with positive/negative anomalies during El Niño/La Niña. In a previous study we showed that during the 1997 - 1998 El Niño, a positive anomaly observed in the global mean sea level was mostly caused by an increase of the ocean mass component rather than by steric (thermal) effects. This result was related to an increase of precipitation over the tropical ocean and a deficit in land water storage. In the present study, we investigate the effect of the recent 2008 and 2011 La Niña events on the satellite altimetry-based global mean sea level. We find that the large global mean sea level drop associated with the 2011 La Niña results from the combined decrease of the steric and ocean mass components, with a slightly dominant contribution from the latter. We show that the ocean mass contribution to the global mean sea level drop is spatially confined over the north eastern tropical Pacific (just as was found previously for the 1997 - 1998 El Niño, but with opposite sign). Corresponding ocean mass spatial pattern is closely correlated to observed sea level and steric spatial patterns over the duration of the La Niña event. This is also observed for previous El Niño and La Niña events. Such a drop in ocean mass during ENSO in the eastern part of the tropical Pacific has not been reported before. It is possibly related to a temporary decrease in the net precipitation over the north eastern Pacific (opposite situation was found during the 1997 - 1998 El Niño).

Open Access March 17, 2014

On The Errors-In-Variables Model With Singular Dispersion Matrices

B. Schaffrin, K. Snow, F. Neitzel

More Download PDF

Abstract

While the Errors-In-Variables (EIV) Model has been treated as a special case of the nonlinear Gauss- Helmert Model (GHM) for more than a century, it was only in 1980 that Golub and Van Loan showed how the Total Least-Squares (TLS) solution can be obtained from a certain minimum eigenvalue problem, assuming a particular relationship between the diagonal dispersion matrices for the observations involved in both the data vector and the data matrix. More general, but always nonsingular, dispersion matrices to generate the “properly weighted” TLS solution were only recently introduced by Schaffrin and Wieser, Fang, and Mahboub, among others. Here, the case of singular dispersion matrices is investigated, and algorithms are presented under a rank condition that indicates the existence of a unique TLS solution, thereby adding a new method to the existing literature on TLS adjustment. In contrast to more general “measurement error models,” the restriction to the EIV-Model still allows the derivation of (nonlinear) closed formulas for the weighted TLS solution. The practicality will be evidenced by an example from geodetic science, namely the over-determined similarity transformation between different coordinate estimates for a set of identical points.

Open Access April 12, 2014

Global Eustatic Sea-Level Variations for the Approximation of Geocenter Motion from Grace

Inga Bergmann-Wolf, Liangjing Zhang, Henryk Dobslaw

More Download PDF

Abstract

Global degree-1 coefficients are derived by means of the method by Swenson et al. (2008) from a model of ocean mass variability and RL05 GRACE monthly mean gravity fields. Since an ocean model consistent with the GRACE GSM fields is required to solely include eustatic sea-level variability which can be safely assumed to be globally homogeneous, it can be empirically derived from GRACE aswell, thereby allowing to approximate geocenter motion entirely out of the GRACE monthly mean gravity fields. Numerical experiments with a decade-long model time-series reveal that the methodology is generally robust both with respect to potential errors in the atmospheric part of AOD1B and assumptions on global degree-1 coefficients for the eustatic sea-level model. Good correspondence of the GRACE RL05-based geocenter estimates with independent results let us conclude that this approximate method for the geocenter motion is well suited to be used for oceanographic and hydrological applications of regional mass variability from GRACE,where otherwise an important part of the signal would be omitted.

About this journal

Journal of Geodetic Science is a peer-reviewed, electronic-only journal that publishes original, high-quality research on topics broadly related to Geodesy. The journal focuses on theoretical and application papers. The aim of the Journal is to become a premier source of knowledge and a worldwide-recognized platform of exchange for scientists of different disciplinary origins and backgrounds (e.g., Surveyors, Geodesists and Geophysicists). The journal publishes geodetic research from a broad range of topics and approaches including Geodetic Networks, Deformation analysis, Adjustment theory and application of mathematical statistics, Satellite Geodesy, Physical Geodesy, Geodynamics, Geometric Geodesy, (see the scope listed below for more). However, we will accept both theoretical and empirical contributions in all subfields of Geodesy as long as they contribute in a broad sense to the core theme.

The scope includes, but is not restricted to:

Surveying Engineering
Geodetic Networks
Deformation Analysis
Adjustment Theory and Mathematical Geodesy
Global Navigation Satellite Systems (GNSS)
Inertial Geodesy
Geoid determination and height systems
Marine Geodesy and Satellite Altimetry
Satellite Gravimetry
Geometric Geodesy
Numerical methods and software developments in Geodesy
Geodynamics
Geophysical Geodesy

Journal Partners