2000A&A...359.1201F

Several hundreds of compact extragalactic radiosources (mainly quasars, but also BL Lac and galaxies) are monitored in a series of permanent VLBI geodetic and astrometric programs that were initiated in the late 1970's in support to the solar system exploration, for studying the Earth's rotation and crustal deformations, and for creating the celestial reference frame later recommended by the IAU as the International Celestial Reference Frame (ICRF). Time series of directions of ICRF objects can be established at a sub-milliarcsecond precision level. A subset of 16 objects with a dense observational history over 1988-1999 are studied in order to derive information on the geometric and statistical properties of their emission at centimetric wavelength.