  The event rate and the efficiency of mass estimation for free-floating planet
(FFP) microlensing events were determined from the simulation of the
simultaneous parallax observations by Euclid, WFIRST, and LSST. The stellar
population from the Besan\c{c}on Galactic model toward $(l,
b)=(1^{\circ},-1.^{\circ}75)$ was applied to our 3D microlensing model, and
30,000 parallax observations were simulated for each following FFP lens masses:
Jupiter-mass, Neptune-mass, and Earth-mass assuming the population of one FFP
per star. The interstellar dust, unresolved stellar background, nearby star
blending were modelled. A signal-to-noise limit considering a finite source
effect determined the event detectability. The Euclid-WFIRST combination
yielded 30.7 Jupiter-mass FFPs during two 30-day-periods per year in parallax
observation. The parallax event rate decreases to 3.9 FFPs for Earth-mass
planets. The mass estimation from the parallax light curve allowed recovery of
FFP masses to within a factor of two for 20-26% of cases. The Euclid-LSST
combination yielded 34.5 Jupiter-mass FFPs down to 0.5 Earth-mass FFPs for the
same periods and the mass is recovered to within a factor of two in 20-40% of
cases. The event rate will be normalised by the unknown FFP abundance to
recover the number of expected detections.
