  The collision processes of two crescentic dunes called barchans are
systematically studied using a simple computer simulation model. The simulated
processes, coalescence, ejection and reorganization, qualitatively correspond
to those observed in a water tank experiment. Moreover we found the realized
types of collision depend both on the mass ratio and on the lateral distance
between barchans under initial conditions. A simple set of differential
equations to describe the collision of one-dimensional (1D) dunes is
introduced.
