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Water vapour (WV) plays a fundamental role in several weather processes that deeply influence human activities. Satellite based radiometers, Ground based Global Navigation Satellite Systems (GNSS) and Numerical Weather Models (NWM) permit to obtain either measurements or estimates or forecasts of WV. This work presents a 2 years systematic comparison to address the agreement on the tropospheric wet delay retrieved by the three mentioned independent techniques over permanent stations belonging to SIRGAS (Sistema de Referencia para las Américas) GNSS network. SIRGAS tropospheric total delay estimations are compared with the official International GNSS Service (IGS) ones, with the measurements from the Jason-1 satellite radiometer (JMR) in terms of Zenith Wet Delays (ZWD) and, finally, with the ZWD computed from ERA Interim, the last reanalysis dataset from the European Center for Medium-Range Weather Forecasts (ECMWF). All the differences between the techniques, which were considered in order to yield a reliable comparison, are discussed. . It has been clearly understood that the knowledge of high accurate WV content and its distribution in the atmosphere improves short term weather forecasts significantly. At the same time, WV reveals very rapid changes both in the temporal and in the spatial domains such that, at present, there are no theoretical models that can reliably predict its behaviour. Retrieving WV content in the atmosphere can be performed in different ways using independent techniques: starting from the more traditional and established ones, such as radiosondes and ground-based microwave radiometers, up

(IAG) also had its quadrennial General Assembly. The IAG co-organised and contributed to several Union Symposia, as well as to Joint Symposia with other Associations. It also organised seven symposia of its own, one dedicated to each of the four commissions and three dedicated to specific scientific issues. This volume contains the proceedings of 13 symposia, which are listed below with the name of their associate editor(s):

Abstract. Satellite positioning systems allow the fixing of the location of a point on the Earth's surface with very good precision and accuracy. To do this, however, it is necessary to determine the point coordinates taking account the reference system and the movements that affect them because of tectonic plate movements. These reference systems are materialized by a significant number of continuous measurement stations in South America. In SIRGAS (Sistema de Referencia Geocéntrico para las Américas), there are four Analysis Centers that process the data collected from satellites of the Global Navigation Satellite Systems (GNSS), with the primary purpose to maintain the international terrestrial reference frame through calculation of the coordinates and velocities of the continuous GNSS stations of the SIRGAS-CON Network.In this work, we demonstrate the quality of the solutions from CIMA, one of the SIRGAS official processing centers operating in Mendoza, Argentina, in comparison with other South American processing centers. The importance of precise calculations of coordinates and velocities in a global frame is also shown. Finally, we give estimations of velocities from stations located within deformation zones in the Central Andes.