The ITRF96 realization and its associated velocity field

This text intends to present and to analyse the quality of the new 1996 edition of the International Terrestrial Reference System, called the ITRF96. The ITRF96 represents a key step forward in the activity of the IERS terrestrial system determinations: a new physical combination model has been developed as well as a new stochastic model. For the first time, the level of accuracy has reached 1 cm (or better) in position for about 50% of ITRF96 stations and 30% of the stations have their velocities determined, free of any aditional tectonic plate model assumption, with an uncertainty better than 3 mm/yr. The ITRF96 also provides a more complete solution: a new software has been developed which makes available the ITRF96 full variance-covariance matrix whereas this information was restricted to station positions in the previous ITRF94 edition. Moreover, the network coverage is clearly the largest set of globally distributed terrestrial Space Geodesy stations that have ever been computed: 521 stations located among 290 sites. In addition, station velocities are also determined at a very accurate level allowing possible determination of kinematic plate motion models free of any geological assumption.