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monument, maintain and operate. Plus, they contribute good observations that permit
obtaining the needed and required results and precisions for the searched object.
In this thesis I develop the methodology used in the densification of the international
reference system (ITRF) through one of its spatial techniques, the GPS. The IGS is what
regulates and centralizes this contribution.
The first chapter introduces the reader in the uses and necessities for having a high accuracy
reference system that in addition will remain stable along time. We present four practical
examples of the requirement of the precise and global reference system, starting from
scientific and professional goals.
Since the definition of the reference system is technical it is necessary materializing it on the
terrestrial surface. The second chapter briefly describes the frames that carry out this work
beginning with the development of the ITRF 2008 (International Terrestrial Reference Frame)
and the ITRF 2005, plus the parameters that relate them. Afterwards follows the description
of the contribution of the GNS observations through the IGS to said materialization. Finally
comes how the IGS05 is regionally densified from the SIRGAS and its processing centers.
The third chapter methodologically describes the rigorous processing of a network of regional
continuous operation in South America (SIRGAD-CON-D-Sur). It refers to the models used in
the processing and determination of parameters, especially to the coordinates of the stations
conforming the network.
The fourth and fifth chapters are destined to analyzing the results. Chapter 4th takes the
normal equations of a regional network (SIRGAS-CON-D-Sur) that is weekly processed to
perform an internal precision analysis. It is carried out with an adjustment of daily solutions to
obtain a weekly solution previous to the introduction of the datum. As an analysis, the
reference frame is introduced through two adjustment strategies, with two different types of
coordinates (IGS05+vel and IGS-Weekly) trying to determine which methodology is the most
adequate for the regional densification of the IGS05 reference frame.
The fifth chapter develops the methodology used to assess the precise velocities. Later on
there is the analysis of the seasonal variations that present many coordinates series,
especially in height, as they are not represented by the estimated lineal velocities. In order to
respond to this seasonal behavior we analyze the correlation between height variation and
the variation of the atmospheric pressure at the observation site.
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