  The EFIELD instrument is part of the geophysics and meteorology sensor
package DraGMet on the Dragonfly mission, which will explore the surface of
Titan in the mid-2030s. EFIELD consists of two electrodes designed to passively
record the AC electric field at each landing site.
  The exploration zone of Dragonfly will mostly consist of dune fields, covered
with sand grains. Little is known on the properties of these grains, although
Cassini-Huygens observations suggest they are mostly made of organic material
produced by Titan's atmospheric photochemistry and evolved at the surface.
Little is known also about dune formation and in general about the transport of
sediments by winds. The latter much depends on inter-particle forces and
therefore on how grains are charged by friction. We demonstrate here that the
EFIELD experiment can bring new insights on these questions.
  We have developed a hydrodynamic-electrostatic model to simulate the
trajectory of a wind-blown charged sand grain in the vicinity of an idealized
EFIELD probe and to predict how such a grain flying close to the probe would
affect its potential. We show that, in some conditions, the resulting
perturbation will be strong enough to be detected by the EFIELD probe. More
specifically, we find that the detection of typical charged wind-blown grains
(200 microns) on Titan requires an instrument standard deviation noise inferior
to 1mV, though occasional larger grains flying close to one electrode could be
detected with a higher noise level.
  Furthermore, we propose a method to retrieve information on the charge and
velocity of wind-blown charged grains detected by the EFIELD experiment. This
method well applies for cases where the particle trajectory can be regarded as
quasi-linear. We validate our inversion approach on both synthetic and
experimental data obtained with a laboratory prototype of the EFIELD
experiment.
