  The GBOT group is in charge of the Ground Based Optical Tracking of the Gaia
satellite. In concrete terms, since the launch of Gaia, our task is to take
every night, using ground based medium-class telescopes, short sequences of
$10$ or $20$ images of the Gaia satellite close to its meridian transit. For
this purpose, we mainly use the VLT Survey Telescope and the Liverpool
Telescope. In these images, taken close to the Sun's opposition - since Gaia is
in L$_2$ - we observe many asteroids: between $30$ and $100$ asteroids every
night, up to magnitude $22$. In order to extract the astrometric positions as
well as the magnitudes of these asteroids, we have developed semi-automatic
methods, strategies and tools tailored explicitly for this daily task. In only
three and a half years of operation, this system has allowed us to send to the
Minor Planet Center the position and the photometry for about $20,000$
asteroids, amongst which $9,000$ new objects. Here we describe all the aspects
of the GBOT asteroid survey.
