|Three Body Scattering" is a phenomenon that occurs primarily when
large hail is forming in the atmosphere. Since the hail is so large
and so reflective, a significant amount of the energy of the radar
beam reflects off the hail and down towards the ground. The enery then
bounces off the ground and again hits the reflective hail which again
scatters the energy, part of which is received a second time by the
radar. So instead of the hail producing a single radar return, it can
produce multiple returns along the same radial as energy is bounced
off the ground and again off the hail.
This causes a characteristic spike as shown in the image above
angling off to the northwest and is known as a "Three Body Scattering
Spike" (TBBS). The spike is not real in that the location of the spike
doesn't really represent real hail in that location--however, where
the spike begins can provide very valuable information as to where
large hail is forming.