INVESTIGADORES
MACKERN OBERTI maria Virginia
congresos y reuniones científicas
Título:
Datum realization for the SIRGAS weekly coordinates
Autor/es:
M. V. MACKERN; L.SANCHEZ
Lugar:
Buenos Aires
Reunión:
Congreso; IAG 2009 Scientific Assembly; 2009
Institución organizadora:
International Asociation of Geodesy
Resumen:
At present,
SIRGAS (Sistema de Referencia Geocéntrico para las Américas) is realized by a
network of continuously operating GNSS stations (SIRGAS-CON) with about 190
sites distributed over Latin America and the Caribbean.
This network comprises a continental (core) network and three densification
sub-networks, which are weekly processed by the SIRGAS Analysis Centres. In the
analysis procedure, each sub-network is individually processed by fixing IGS satellite
orbits and IGS Earth Orientation Parameters and by giving an a priori sigma of 1 m to all coordinate stations.
These loosely constrained solutions are weekly combined in a unified solution
with two main products: loosely constrained combinations in SINEX format for
later computations (for instance multiyear solutions) and weekly constrained
coordinates for practical applications (for instance as reference for differential
GNSS surveying). Traditionally, constrained coordinates are obtained after
applying the no-net rotation (NNR) and no-net translation (NNT) conditions with
respect to the IGS05 values for the IGS05 stations included in the SIRGAS-CON
network. However, after comparing SIRGAS weekly coordinates with the IGS weekly
solutions for common stations, inconsistencies up to the 1-cm level are found. In
order to analyse these discrepancies and to identify possible network
deformations due to fixing the geodetic datum, different strategies for the
datum realization within the SIRGAS-CON network are evaluated: 1) Fixing
coordinates for IGS05 stations, 2) Constraining coordinates for IGS05 stations
applying as a priori sigma 1E-05
m, and 3) NNR+NNT with respect to IGS05 stations. These
three strategies are numerically evaluated using both the IGS05 values (i.e. IGS05
coordinates + velocities to reduce reference values from reference epoch 2000.0
to observation epoch) and the IGS weekly constrained coordinates (i.e.
igsyyPwwww solutions). Linear velocities included in the IGS05 solution do not
represent seasonal variations in station positions and reduced coordinates (by
means of these velocities) are only approximate. Discrepancies between these approximate
coordinates and the actual position of the reference stations (up to 3 cm) deform the network geometry,
mainly at the borders. This deformation is minimized by applying IGS weekly
coordinates in combination with the NNR+NNT strategy. This paper presents
numerical results after applying the described strategies to SIRGAS-CON weekly
solutions for the period between October 1, 2006 and December 31, 2008.
Obtained conclusions can be generalized for the datum realization of regional
reference frames.