Twenty years of evolution for the DORIS permanent network: from its initial deployment to its renovation

The ground network is one of the major components of the DORIS system. Its deployment, managed by the French national mapping agency [Institut Geographique National, (IGN)], started in 1986 at a sustained pace that allowed it to reach 32 stations upon the launch of the first DORIS-equipped satellite (SPOT-2) in 1990. For the first generation of transmitting antennas, the installation procedures were adapted to the decimetre performance objective for the DORIS system. During the second era of the deployment of an even denser network, the antenna support layouts gradually evolved towards a better quality, thus improving the long-term stability of the antenna reference point, and a new antenna model allowed a more accurate survey. As the positioning accuracy of the DORIS system improved, it was necessary to review the antenna stability for the whole network. A first stability estimation, using criteria like antenna model and support design, was followed by a major renovation effort which started in 2000 and is now almost complete. In 6 years, through the renovation or installation of 43 stations and the implementation of new installation procedures to meet more stringent stability requirements, significant improvement in network quality was achieved. Later a more analytical approach, taking into account the characteristics of each element that support the antenna, has been taken to assess the potential stability of all DORIS occupations. IGN is also in charge of its operational maintenance, an intensive activity on account of the significant failure rate of the successive generations of equipment. Nevertheless, thanks to its unique density and homogeneity, DORIS has maintained a very good coverage rate of the satellite orbits. Through 38 well-distributed current co-locations with the Global Positioning System, Satellite Laser Ranging and Very Long Baseline Interferometry techniques in its current 56-station network, DORIS contributes significantly to the realisation of the International Terrestrial Reference System. DORIS stations in areas where no other space geodesy technique is available provide a significant contribution to the study of plate tectonics. Many stations co-located with tide gauges contribute to the monitoring of sea level changes. Although it has several advantages over similar techniques, there is still room for improvement in the DORIS network.