  Astrometric observations of microlensing events can be used to obtain
important information about lenses. During these events, the shift of the
position of the multiple image centroid with respect to the source star
location can be measured. This effect, which is expected to occur on scales
from micro-arcseconds to milli-arcseconds, depends on the lens-source-observer
system physical parameters. Here, we consider the astrometric and photometric
observations by space and ground-based telescopes of microlensing events
towards the Galactic bulge caused by free floating planets (FFPs). We show that
the efficiency of astrometric signal on photometrically detected microlensing
events tends to increase for higher FFP masses in our Galaxy. In addition, we
estimate that during five years of the Gaia observations, about a dozen of
microlensing events caused by FFPs are expected to be detectable.
