  The Rees-Sciama effect produced in mergers of galaxy clusters is discussed,
and an analytical approximation to compute this effect from numerical
simulations is given. Using this approximation and a novel toy model describing
the physics of the merger, we characterize the spatial properties and
symmetries of the Rees-Sciama signal. Based on these properties, we propose a
method to extract the physical parameters of the merger, which relies on the
computation of the quadrupole moment of the observed brightness distribution on
the sky. The relationships between the quadrupole coefficients and the physical
parameters of the merger (physical separation, projection angle on the sky and
angular momentum) are discussed. Finally, we propose a method to co-add
coherently the RS signals from a sample of cluster mergers, in order to achieve
an statistical detection of the effect for those cases where individual signals
are masked by the kinetic SZ effect, the primordial CMB components, and by
observational noise.
