  We propose a framework for monostatic sensing by a user equipment (UE), aided
by a reconfigurable intelligent surface (RIS) in environments with single- and
double-bounce signal propagation. We design appropriate UE-side precoding and
combining, to facilitate signal separation. We derive the adaptive detection
probabilities of the resolvable signals, based on the geometric channel
parameters of the links. Then, we estimate the passive objects using both the
double-bounce signals via passive RIS (i.e., RIS-sensing) and the single-bounce
multipath direct to the objects (i.e., non-RIS-sensing), based on a mapping
filter. Finally, we provide numerical results to demonstrate that effective
sensing can be achieved through the proposed framework.
