References of "International Association of Geodesy Symposia"
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See detailImpact of Limited Satellite Visibility on Estimates of Vertical Land Movements
Abraha, Kibrom Ebuy UL; Teferle, Felix Norman UL; Hunegnaw, Addisu UL et al

in International Association of Geodesy Symposia (2016)

The number of Global Navigation Satellite System (GNSS) satellites and their geometry directly affect the quality of positioning and derived satellite products. Accordingly, the International GNSS Service ... [more ▼]

The number of Global Navigation Satellite System (GNSS) satellites and their geometry directly affect the quality of positioning and derived satellite products. Accordingly, the International GNSS Service (IGS) recommends GNSS antennas to be installed away from natural and man-made surfaces and structures, which may affect the incoming signals through severe multipath or obstructions. Following these recommendations, continuous GNSS (cGNSS) stations are generally located in low multipath environments with minimal signal obstructions. However, some applications require GNSS antennas to be installed at specific locations in order to measure local processes. In support of sea level studies, cGNSS stations are established at or close to tide gauges in order to accurately monitor the local vertical land movements experienced by the sea level sensors. However, the environment at the tide gauge might not be optimal for GNSS observations due to the aforementioned station-specific effects, which may degrade the quality of coordinate solutions. This study investigates the impact of severe signal obstructions on long-term position time series for some selected stations. A masking profile from an actually obstructed site is extracted, simulated and applied to unobstructed IGS sites. To investigate these effects, we imple- mented a new feature called azimuth-dependent elevation masking in the Bernese GNSS Software version 5.2. We present our preliminary results on the use of this new feature to study the impact of different obstruction scenarios on long-term GNSS position time series and vertical land movement estimates. The results show that a certain obstruction, with the effect being highly dependent on its severity and azimuthal direction, affects all coordinate components with the effect being more significant for the Up component. Moreover, it causes changes in the rate estimates and increases the rate uncertainty with the effect being site-specific. [less ▲]

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See detailStatus of TIGA activities at the British Isles continuous GNSS Facility and the University of Luxembourg
Hunegnaw, Addisu UL; Teferle, Felix Norman UL; Bingley, Richard et al

in International Association of Geodesy Symposia (2016), 143

In 2013 the InternationalGNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to reanalyse all relevant GPS observations from 1995 to ... [more ▼]

In 2013 the InternationalGNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to reanalyse all relevant GPS observations from 1995 to the end of 2012 in order to provide high quality estimates of vertical land motion for monitoring of sea level changes. The TIGA Working Group will also produce a combined solution from the individual TIGA Analysis Centres (TAC) contributions. The consortium of British Isles continuous GNSS Facility (BIGF) and the University of Luxembourg TAC (BLT) will contribute weekly minimally constrained SINEX solutions from its reprocessing using the Bernese GNSS Software (BSW) version 5.2 and the University of Luxembourg will also act as a TIGA Combination Centre (TCC). The BLT will generate two solutions, one based on BSW5.2 using a network double difference (DD) strategy and a second one based on BSW5.2 using a Precise Point Positioning (PPP) strategy. In the DD strategy we have included all IGb08 core stations in order to achieve a consistent reference frame implementation. As an initial test for the TIGA combination, all TACs agreed to provide weekly SINEX solutions for a four-week period in December 2011. Taking these individual TAC solutions the TCC has computed a first combination using two independent combination software packages: CATREF and GLOBK. In this study we will present preliminary results from the BLT reprocessing and from the combination tests [less ▲]

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See detailNew Estimates of Present-Day Crustal/Land Motions in the British Isles Based on the BIGF Network
Hansen, Dionne; Teferle, Felix Norman UL; Bingley, Richard M et al

in International Association of Geodesy Symposia (2012), 136

n this study we present results from a recent reprocessing effort that included data from more than 120 continuous Global Positioning System (CGPS) stations in the British Isles for the period from 1997 ... [more ▼]

n this study we present results from a recent reprocessing effort that included data from more than 120 continuous Global Positioning System (CGPS) stations in the British Isles for the period from 1997 to 2008. Not only was the CGPS network dramatically densified from previous investigations by the authors, it now also includes, for the first time, stations in Northern Ireland, providing new constraints on glacio-isostatic processes active in the region. In our processing strategy we apply a combination of re-analysed satellite orbit and Earth rotation products together with updated models for absolute satellite and receiver antenna phase centers, and for the computation of atmospheric delays. Our reference frame implementation uses a semi-global network of 37 stations, to align our daily position estimates, using a minimal constraints approach, to ITRF2005. This network uses a combination of current IGS reference frame stations plus additional IGS stations in order to provide similar network geometries throughout the complete time span. The derived horizontal and vertical station velocities are used to investigate present-day crustal/land motions in the British Isles. This first solution provides the basis for our contri- bution to the Working Group on Regional Dense Velocity Fields, 2007 - 2011 of the International Asso- ciation of Geodesy Subcommission 1.3 on Regional Reference Frames. [less ▲]

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See detailInvestigation of hydrological and atmospheric loading by space geodetic techniques
Schuh, H.; Eastermann, G.; Cretaux, J.-F. et al

in International Association of Geodesy Symposia (2003), 126

Observations of sea level can only be interpreted correctly if land motion in particular in terms of vertical deformation of coastal areas is taken into account. In the last decades space geodetic ... [more ▼]

Observations of sea level can only be interpreted correctly if land motion in particular in terms of vertical deformation of coastal areas is taken into account. In the last decades space geodetic techniques such as VLBI (Very Long Baseline Interferometry), SLR (Satellite Laser Ranging), the GPS (Global Positioning System), and Doris (Doppler Orbitography and Radio positioning Integrated by Satellite) have proved to be very powerful for determining displacements of points on the solid Earth. These can be modeled by using various geodynamical parameters, e.g. the Love and Shida numbers in the model of the solid Earth tides and site-dependent amplitudes and phases of the ocean loading models. Today, the small deformations associated with the response of the Earth to atmospheric and hydrological loading are of growing interest. These effects cause site-dependent vertical displacements with ranges up to ±30mm due to atmospheric pressure variations and due to mass redistribution in surface fluid envelopes, in particular in continental water reservoirs (soil moisture, snow, and groundwater). Several new global and regional models of soil moisture and snow depths are now available and can be validated by space geodetic techniques. This paper is intended to give a short overview about state-of-the-art of modeling loading effects. A short introduction to the Special Bureau for Loading within the Global Geophysical Fluid Center (GGFC) of the IERS will be given, too. Finally, it will be shown how the effects influence the results of high precision space geodetic measurements. The paper mainly concentrates on vertical crustal motions on seasonal and interannual time scales observed by VLBI and describes also some results obtained from Doris. [less ▲]

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