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| Titel |
GPS and DORIS evidence for a very slow subsidence of Tahiti Island |
| VerfasserIn |
Abdelali Fadil, Jean-Pierre Barriot, Lydie Sichoix, Pascal Ortéga |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036363
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| Zusammenfassung |
| A decade of GPS (Global Positioning System) and DORIS (Doppler Orbitography and
Radiopositioning Integrated by Satellite) observations were analyzed to monitor the vertical
displacement of the Tahiti Island. The local network consisted of co-located two GPS stations
(THTI and TAH1) and a DORIS beacon (PAQB). While DORIS weekly series of station
positions were computed by the IGN/JPL group (Institut Géographique National and the Jet
Propulsion Laboratory) using GIPSY-OASIS II software, two different GPS processing
modes were adopted.
In the first one, GPS data from 20 IGS (International GPS Service) stations located in and
around the Pacific plate were processed using GAMIT-GLOBK software in its
standard three-step approach. We estimated station coordinates, tropospheric zenith
delays, horizontal gradients, and orbital and earth orientation parameters (EOP)
parameters. The regional quasi-observations have been combined with quasi-observations
from an analysis of GPS data from over 300 stations performed by the MIT group
(Massachusetts Institute of Technology). The GPS solution was realized in a global
reference frame by estimating a 14-parameter transformation between our loosely
constrained GPS analysis and the known ITRF2005 positions and velocities of 46 IGS
stations.
In the second one, only THTI and TAH1 data have been reduced with respect to the precise
point positioning PPP mode of GIPSY-OASIS II software using the new JPL final
clocks and orbits. Each daily solution was aligned to the ITRF2005 reference frame.
Solid earth and polar tide corrections following the IERS Conventions 2003, ocean
loading corrections using the FES2004 ocean tide model, antenna phase center
models, and the Vienna Mapping Fucntion VMF were taken into account in both
softwares.
Before estimating velocities, time series were cleaned to remove outliers and analyzed for
their noise properties, periodic signals and earthquake and antenna jumps. The GPS and
DORIS vertical velocity fields were very consistent and revealed a very slow subsidence at
the level of -0.3 mm/yr which is barely significant but in a good agreement with the lower
range of coral reef stratigraphy rate estimated at -0.25 mm/yr. Results were sensitive to the
reference frame scale factor. |
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